[dpdk-dev,v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest

  From: "vadim.suraev@gmail.com" <vadim.suraev@gmail.com>

This patch adds mbuf bulk allocation/freeing functions and unittest

Signed-off-by: Vadim Suraev
<vadim.suraev@gmail.com>
---
New in v2:
    - function rte_pktmbuf_alloc_bulk added
    - function rte_pktmbuf_bulk_free added
    - function rte_pktmbuf_free_chain added
    - applied reviewers' comments

 app/test/test_mbuf.c       |   94 +++++++++++++++++++++++++++++++++++++++++++-
 lib/librte_mbuf/rte_mbuf.h |   91 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 184 insertions(+), 1 deletion(-)
  

On Wed, Mar 18, 2015 at 10:21:18PM +0200, vadim.suraev@gmail.com wrote:
> From: "vadim.suraev@gmail.com" <vadim.suraev@gmail.com>
> 
> This patch adds mbuf bulk allocation/freeing functions and unittest
> 
> Signed-off-by: Vadim Suraev
> <vadim.suraev@gmail.com>
> ---
> New in v2:
>     - function rte_pktmbuf_alloc_bulk added
>     - function rte_pktmbuf_bulk_free added
>     - function rte_pktmbuf_free_chain added
>     - applied reviewers' comments
> 
>  app/test/test_mbuf.c       |   94 +++++++++++++++++++++++++++++++++++++++++++-
>  lib/librte_mbuf/rte_mbuf.h |   91 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 184 insertions(+), 1 deletion(-)
> 
> diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
> index 1ff66cb..b20c6a4 100644
> --- a/app/test/test_mbuf.c
> +++ b/app/test/test_mbuf.c
> @@ -77,6 +77,7 @@
>  #define REFCNT_RING_SIZE        (REFCNT_MBUF_NUM * REFCNT_MAX_REF)
>  
>  #define MAKE_STRING(x)          # x
> +#define MBUF_POOL_LOCAL_CACHE_SIZE 32
>  
>  static struct rte_mempool *pktmbuf_pool = NULL;
>  
> @@ -405,6 +406,84 @@ test_pktmbuf_pool(void)
>  	return ret;
>  }
>  
><snip>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 17ba791..fabeae2 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -825,6 +825,97 @@ static inline void rte_pktmbuf_free(struct rte_mbuf *m)
>  }
>  
>  /**
> + * Allocate a bulk of mbufs, initiate refcnt and resets
> + *
> + * @param pool
> + *    memory pool to allocate from
> + * @param mbufs
> + *    Array of pointers to mbuf
> + * @param count
> + *    Array size
> + */
> +static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool,
> +					 struct rte_mbuf **mbufs,
> +					 unsigned count)
> +{
> +	unsigned idx;
> +	int rc = 0;
> +
> +	rc = rte_mempool_get_bulk(pool, (void **)mbufs, count);
> +	if (unlikely(rc))
> +		return rc;
> +
> +	for (idx = 0; idx < count; idx++) {
> +		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
> +		rte_mbuf_refcnt_set(mbufs[idx], 1);
> +		rte_pktmbuf_reset(mbufs[idx]);
> +	}
> +	return rc;
> +}
> +
> +/**
> + * Free a bulk of mbufs into its original mempool.
> + * This function assumes:
> + * - refcnt equals 1
> + * - mbufs are direct
> + * - all mbufs must belong to the same mempool
> + *
> + * @param mbufs
> + *    Array of pointers to mbuf
> + * @param count
> + *    Array size
> + */
> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> +					 unsigned count)
> +{
> +	unsigned idx;
> +
> +	RTE_MBUF_ASSERT(count > 0);
> +
> +	for (idx = 0; idx < count; idx++) {
> +		RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> +		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> +		rte_mbuf_refcnt_set(mbufs[idx], 0);
This is really a misuse of the API.  The entire point of reference counting is
to know when an mbuf has no more references and can be freed.  By forcing all
the reference counts to zero here, you allow the refcnt infrastructure to be
circumvented, causing memory leaks.

I think what you need to do here is enhance the underlying pktmbuf interface
such that an rte_mbuf structure has a destructor method association with it
which is called when its refcnt reaches zero.  That way the
rte_pktmbuf_bulk_free function can just decrement the refcnt on each
mbuf_structure, and the pool as a whole can be returned when the destructor
function discovers that all mbufs in that bulk pool are freed.

Neil
  

Hi Neil,

On 03/18/2015 09:58 PM, Neil Horman wrote:
>> +/**
>> + * Free a bulk of mbufs into its original mempool.
>> + * This function assumes:
>> + * - refcnt equals 1
>> + * - mbufs are direct
>> + * - all mbufs must belong to the same mempool
>> + *
>> + * @param mbufs
>> + *    Array of pointers to mbuf
>> + * @param count
>> + *    Array size
>> + */
>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
>> +					 unsigned count)
>> +{
>> +	unsigned idx;
>> +
>> +	RTE_MBUF_ASSERT(count > 0);
>> +
>> +	for (idx = 0; idx < count; idx++) {
>> +		RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
>> +		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
>> +		rte_mbuf_refcnt_set(mbufs[idx], 0);
> This is really a misuse of the API.  The entire point of reference counting is
> to know when an mbuf has no more references and can be freed.  By forcing all
> the reference counts to zero here, you allow the refcnt infrastructure to be
> circumvented, causing memory leaks.
>
> I think what you need to do here is enhance the underlying pktmbuf interface
> such that an rte_mbuf structure has a destructor method association with it
> which is called when its refcnt reaches zero.  That way the
> rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> mbuf_structure, and the pool as a whole can be returned when the destructor
> function discovers that all mbufs in that bulk pool are freed.

I don't really understand what's the problem here. The API explicitly
describes the conditions for calling this functions: the segments are
directs, they belong to the same mempool, and their refcnt is 1.

This function could be useful in a driver which knows that the mbuf
it allocated matches this conditions. I think an application that
only uses direct mbufs and one mempool could also use this function.

Regards,
Olivier
  

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Olivier MATZ
> Sent: Thursday, March 19, 2015 8:41 AM
> To: Neil Horman; vadim.suraev@gmail.com
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest
> 
> Hi Neil,
> 
> On 03/18/2015 09:58 PM, Neil Horman wrote:
> >> +/**
> >> + * Free a bulk of mbufs into its original mempool.
> >> + * This function assumes:
> >> + * - refcnt equals 1
> >> + * - mbufs are direct
> >> + * - all mbufs must belong to the same mempool
> >> + *
> >> + * @param mbufs
> >> + *    Array of pointers to mbuf
> >> + * @param count
> >> + *    Array size
> >> + */
> >> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> >> +					 unsigned count)
> >> +{
> >> +	unsigned idx;
> >> +
> >> +	RTE_MBUF_ASSERT(count > 0);
> >> +
> >> +	for (idx = 0; idx < count; idx++) {
> >> +		RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> >> +		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> >> +		rte_mbuf_refcnt_set(mbufs[idx], 0);
> > This is really a misuse of the API.  The entire point of reference counting is
> > to know when an mbuf has no more references and can be freed.  By forcing all
> > the reference counts to zero here, you allow the refcnt infrastructure to be
> > circumvented, causing memory leaks.
> >
> > I think what you need to do here is enhance the underlying pktmbuf interface
> > such that an rte_mbuf structure has a destructor method association with it
> > which is called when its refcnt reaches zero.  That way the
> > rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> > mbuf_structure, and the pool as a whole can be returned when the destructor
> > function discovers that all mbufs in that bulk pool are freed.
> 
> I don't really understand what's the problem here. The API explicitly
> describes the conditions for calling this functions: the segments are
> directs, they belong to the same mempool, and their refcnt is 1.
> 
> This function could be useful in a driver which knows that the mbuf
> it allocated matches this conditions. I think an application that
> only uses direct mbufs and one mempool could also use this function.

I also don't see anything wrong with that function.
As long, as user makes sure that all mbufs in the bulk satisfy the required conditions it should be ok, I think.
Of course, it's usage is limited, but I suppose the author has some scenario in mind, when introduced it.

Konstantin

> 
> Regards,
> Olivier
  

On Thu, Mar 19, 2015 at 09:41:25AM +0100, Olivier MATZ wrote:
> Hi Neil,
> 
> On 03/18/2015 09:58 PM, Neil Horman wrote:
> >>+/**
> >>+ * Free a bulk of mbufs into its original mempool.
> >>+ * This function assumes:
> >>+ * - refcnt equals 1
> >>+ * - mbufs are direct
> >>+ * - all mbufs must belong to the same mempool
> >>+ *
> >>+ * @param mbufs
> >>+ *    Array of pointers to mbuf
> >>+ * @param count
> >>+ *    Array size
> >>+ */
> >>+static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> >>+					 unsigned count)
> >>+{
> >>+	unsigned idx;
> >>+
> >>+	RTE_MBUF_ASSERT(count > 0);
> >>+
> >>+	for (idx = 0; idx < count; idx++) {
> >>+		RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> >>+		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> >>+		rte_mbuf_refcnt_set(mbufs[idx], 0);
> >This is really a misuse of the API.  The entire point of reference counting is
> >to know when an mbuf has no more references and can be freed.  By forcing all
> >the reference counts to zero here, you allow the refcnt infrastructure to be
> >circumvented, causing memory leaks.
> >
> >I think what you need to do here is enhance the underlying pktmbuf interface
> >such that an rte_mbuf structure has a destructor method association with it
> >which is called when its refcnt reaches zero.  That way the
> >rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> >mbuf_structure, and the pool as a whole can be returned when the destructor
> >function discovers that all mbufs in that bulk pool are freed.
> 
> I don't really understand what's the problem here. The API explicitly
> describes the conditions for calling this functions: the segments are
> directs, they belong to the same mempool, and their refcnt is 1.
> 
> This function could be useful in a driver which knows that the mbuf
> it allocated matches this conditions. I think an application that
> only uses direct mbufs and one mempool could also use this function.
> 


That last condition is my issue with this patch, that the user has to know what
refcnts are.  It makes this api useful for little more than the test case that
is provided with it.  Its irritating enough that for singly allocated mbufs the
user has to know what the refcount of a buffer is before freeing, but at least
they can macrotize a {rte_pktmbuf_refcnt_update; if(rte_pktmbuf_refct_read) then
free} operation.

With this, you've placed the user in charge of not only doing that, but also of
managing the relationship between pktmbufs and the pool they came from.  while
that makes sense for the test case, it really doesn't in any general use case in
which packet processing is ever deferred or queued, because it means that the
application is now responsible for holding a pointer to every packet it
allocates and checking its refcount periodically until it completes.

There is never any reason that an application won't need to do this management,
so making it the purview of the application to handle rather than properly
integrating that functionality in the library is really a false savings.

Regards
Neil

> Regards,
> Olivier
> 
>
  

Hi Neil,

On 03/19/2015 02:16 PM, Neil Horman wrote:
>> On 03/18/2015 09:58 PM, Neil Horman wrote:
>>>> +/**
>>>> + * Free a bulk of mbufs into its original mempool.
>>>> + * This function assumes:
>>>> + * - refcnt equals 1
>>>> + * - mbufs are direct
>>>> + * - all mbufs must belong to the same mempool
>>>> + *
>>>> + * @param mbufs
>>>> + *    Array of pointers to mbuf
>>>> + * @param count
>>>> + *    Array size
>>>> + */
>>>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
>>>> +					 unsigned count)
>>>> +{
>>>> +	unsigned idx;
>>>> +
>>>> +	RTE_MBUF_ASSERT(count > 0);
>>>> +
>>>> +	for (idx = 0; idx < count; idx++) {
>>>> +		RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
>>>> +		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
>>>> +		rte_mbuf_refcnt_set(mbufs[idx], 0);
>>> This is really a misuse of the API.  The entire point of reference counting is
>>> to know when an mbuf has no more references and can be freed.  By forcing all
>>> the reference counts to zero here, you allow the refcnt infrastructure to be
>>> circumvented, causing memory leaks.
>>>
>>> I think what you need to do here is enhance the underlying pktmbuf interface
>>> such that an rte_mbuf structure has a destructor method association with it
>>> which is called when its refcnt reaches zero.  That way the
>>> rte_pktmbuf_bulk_free function can just decrement the refcnt on each
>>> mbuf_structure, and the pool as a whole can be returned when the destructor
>>> function discovers that all mbufs in that bulk pool are freed.
>>
>> I don't really understand what's the problem here. The API explicitly
>> describes the conditions for calling this functions: the segments are
>> directs, they belong to the same mempool, and their refcnt is 1.
>>
>> This function could be useful in a driver which knows that the mbuf
>> it allocated matches this conditions. I think an application that
>> only uses direct mbufs and one mempool could also use this function.
> 
> 
> That last condition is my issue with this patch, that the user has to know what
> refcnts are.  It makes this api useful for little more than the test case that
> is provided with it.  Its irritating enough that for singly allocated mbufs the
> user has to know what the refcount of a buffer is before freeing, but at least
> they can macrotize a {rte_pktmbuf_refcnt_update; if(rte_pktmbuf_refct_read) then
> free} operation.
> 
> With this, you've placed the user in charge of not only doing that, but also of
> managing the relationship between pktmbufs and the pool they came from.  while
> that makes sense for the test case, it really doesn't in any general use case in
> which packet processing is ever deferred or queued, because it means that the
> application is now responsible for holding a pointer to every packet it
> allocates and checking its refcount periodically until it completes.
> 
> There is never any reason that an application won't need to do this management,
> so making it the purview of the application to handle rather than properly
> integrating that functionality in the library is really a false savings.

There are some places where you know that the prerequisites are met,
so you can save cycles by using this function.

From what I imagine, if in a driver you allocate mbufs, chain them and
for some reason you realize you have to free them, you can use this
function instead of freeing them one by one.

Also, as it's up to the application to decide how many mbuf pools are
created, and whether indirect mbufs are used or not, the application
can take the short path of using this function in some conditions.

Vadim, maybe you have another reason or use case for adding this
function? Could you detail why you need it and how it improves your
use case?

Regards,
Olivier
  

Hi, Olivier,
No, I personally need to free a chain using mempool bulk. If I'm not
mistaken, it has been proposed by one of reviewers to have lower level
function, so it was done (I'm sorry if misunderstood)
Regards,
Vadim.
On Mar 23, 2015 8:44 PM, "Olivier MATZ" <olivier.matz@6wind.com> wrote:

> Hi Neil,
>
> On 03/19/2015 02:16 PM, Neil Horman wrote:
> >> On 03/18/2015 09:58 PM, Neil Horman wrote:
> >>>> +/**
> >>>> + * Free a bulk of mbufs into its original mempool.
> >>>> + * This function assumes:
> >>>> + * - refcnt equals 1
> >>>> + * - mbufs are direct
> >>>> + * - all mbufs must belong to the same mempool
> >>>> + *
> >>>> + * @param mbufs
> >>>> + *    Array of pointers to mbuf
> >>>> + * @param count
> >>>> + *    Array size
> >>>> + */
> >>>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> >>>> +                                   unsigned count)
> >>>> +{
> >>>> +  unsigned idx;
> >>>> +
> >>>> +  RTE_MBUF_ASSERT(count > 0);
> >>>> +
> >>>> +  for (idx = 0; idx < count; idx++) {
> >>>> +          RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> >>>> +          RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> >>>> +          rte_mbuf_refcnt_set(mbufs[idx], 0);
> >>> This is really a misuse of the API.  The entire point of reference
> counting is
> >>> to know when an mbuf has no more references and can be freed.  By
> forcing all
> >>> the reference counts to zero here, you allow the refcnt infrastructure
> to be
> >>> circumvented, causing memory leaks.
> >>>
> >>> I think what you need to do here is enhance the underlying pktmbuf
> interface
> >>> such that an rte_mbuf structure has a destructor method association
> with it
> >>> which is called when its refcnt reaches zero.  That way the
> >>> rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> >>> mbuf_structure, and the pool as a whole can be returned when the
> destructor
> >>> function discovers that all mbufs in that bulk pool are freed.
> >>
> >> I don't really understand what's the problem here. The API explicitly
> >> describes the conditions for calling this functions: the segments are
> >> directs, they belong to the same mempool, and their refcnt is 1.
> >>
> >> This function could be useful in a driver which knows that the mbuf
> >> it allocated matches this conditions. I think an application that
> >> only uses direct mbufs and one mempool could also use this function.
> >
> >
> > That last condition is my issue with this patch, that the user has to
> know what
> > refcnts are.  It makes this api useful for little more than the test
> case that
> > is provided with it.  Its irritating enough that for singly allocated
> mbufs the
> > user has to know what the refcount of a buffer is before freeing, but at
> least
> > they can macrotize a {rte_pktmbuf_refcnt_update;
> if(rte_pktmbuf_refct_read) then
> > free} operation.
> >
> > With this, you've placed the user in charge of not only doing that, but
> also of
> > managing the relationship between pktmbufs and the pool they came from.
> while
> > that makes sense for the test case, it really doesn't in any general use
> case in
> > which packet processing is ever deferred or queued, because it means
> that the
> > application is now responsible for holding a pointer to every packet it
> > allocates and checking its refcount periodically until it completes.
> >
> > There is never any reason that an application won't need to do this
> management,
> > so making it the purview of the application to handle rather than
> properly
> > integrating that functionality in the library is really a false savings.
>
> There are some places where you know that the prerequisites are met,
> so you can save cycles by using this function.
>
> From what I imagine, if in a driver you allocate mbufs, chain them and
> for some reason you realize you have to free them, you can use this
> function instead of freeing them one by one.
>
> Also, as it's up to the application to decide how many mbuf pools are
> created, and whether indirect mbufs are used or not, the application
> can take the short path of using this function in some conditions.
>
> Vadim, maybe you have another reason or use case for adding this
> function? Could you detail why you need it and how it improves your
> use case?
>
> Regards,
> Olivier
>
  

On Mon, Mar 23, 2015 at 05:44:02PM +0100, Olivier MATZ wrote:
> Hi Neil,
> 
> On 03/19/2015 02:16 PM, Neil Horman wrote:
> >> On 03/18/2015 09:58 PM, Neil Horman wrote:
> >>>> +/**
> >>>> + * Free a bulk of mbufs into its original mempool.
> >>>> + * This function assumes:
> >>>> + * - refcnt equals 1
> >>>> + * - mbufs are direct
> >>>> + * - all mbufs must belong to the same mempool
> >>>> + *
> >>>> + * @param mbufs
> >>>> + *    Array of pointers to mbuf
> >>>> + * @param count
> >>>> + *    Array size
> >>>> + */
> >>>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> >>>> +					 unsigned count)
> >>>> +{
> >>>> +	unsigned idx;
> >>>> +
> >>>> +	RTE_MBUF_ASSERT(count > 0);
> >>>> +
> >>>> +	for (idx = 0; idx < count; idx++) {
> >>>> +		RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> >>>> +		RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> >>>> +		rte_mbuf_refcnt_set(mbufs[idx], 0);
> >>> This is really a misuse of the API.  The entire point of reference counting is
> >>> to know when an mbuf has no more references and can be freed.  By forcing all
> >>> the reference counts to zero here, you allow the refcnt infrastructure to be
> >>> circumvented, causing memory leaks.
> >>>
> >>> I think what you need to do here is enhance the underlying pktmbuf interface
> >>> such that an rte_mbuf structure has a destructor method association with it
> >>> which is called when its refcnt reaches zero.  That way the
> >>> rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> >>> mbuf_structure, and the pool as a whole can be returned when the destructor
> >>> function discovers that all mbufs in that bulk pool are freed.
> >>
> >> I don't really understand what's the problem here. The API explicitly
> >> describes the conditions for calling this functions: the segments are
> >> directs, they belong to the same mempool, and their refcnt is 1.
> >>
> >> This function could be useful in a driver which knows that the mbuf
> >> it allocated matches this conditions. I think an application that
> >> only uses direct mbufs and one mempool could also use this function.
> > 
> > 
> > That last condition is my issue with this patch, that the user has to know what
> > refcnts are.  It makes this api useful for little more than the test case that
> > is provided with it.  Its irritating enough that for singly allocated mbufs the
> > user has to know what the refcount of a buffer is before freeing, but at least
> > they can macrotize a {rte_pktmbuf_refcnt_update; if(rte_pktmbuf_refct_read) then
> > free} operation.
> > 
> > With this, you've placed the user in charge of not only doing that, but also of
> > managing the relationship between pktmbufs and the pool they came from.  while
> > that makes sense for the test case, it really doesn't in any general use case in
> > which packet processing is ever deferred or queued, because it means that the
> > application is now responsible for holding a pointer to every packet it
> > allocates and checking its refcount periodically until it completes.
> > 
> > There is never any reason that an application won't need to do this management,
> > so making it the purview of the application to handle rather than properly
> > integrating that functionality in the library is really a false savings.
> 
> There are some places where you know that the prerequisites are met,
> so you can save cycles by using this function.
> 
> From what I imagine, if in a driver you allocate mbufs, chain them and
> for some reason you realize you have to free them, you can use this
> function instead of freeing them one by one.
> 
> Also, as it's up to the application to decide how many mbuf pools are
> created, and whether indirect mbufs are used or not, the application
> can take the short path of using this function in some conditions.
> 
> Vadim, maybe you have another reason or use case for adding this
> function? Could you detail why you need it and how it improves your
> use case?
> 
> Regards,
> Olivier
> 

So, I think we're making different points here.

You seem to be justifying the API as it exists by finding use cases that fit
into its documented restrictions (direct buffers, refcounts at 1, etc), which
severely limit that use case set.

My assertion is that those restrictions were created because it was
inconvienient to code using the reference count as intended.  I'm saying lets
augment the reference counting mechanism so that we can use these specially
allocated mbufs in a wider variety of use cases beyond the limited set they are
currently good for

Neil
  

Hi Vadim,

> -----Original Message-----

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Vadim Suraev

> Sent: Monday, March 23, 2015 5:31 PM

> To: Olivier MATZ

> Cc: dev@dpdk.org

> Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest

> 

> Hi, Olivier,

> No, I personally need to free a chain using mempool bulk. If I'm not

> mistaken, it has been proposed by one of reviewers to have lower level

> function, so it was done (I'm sorry if misunderstood)


Was it me?
As I remember, I said it would be good to create rte_pktmbuf_bulk_free() or rte_pktmbuf_seg_bulk_free() -
that would free a bulk of mbufs segments in the same manner as rte_pktmbuf_free_chain() does:
count number of consecutive mbufs from the same mempool to be freed and then put them back into the pool at one go.
Such function would be useful inside PMD code.
In fact we already using analogy of such function inside vPMD TX code.
Though from my point, such function should be generic as rte_pktmbuf_free_chain() -
no special limitations like all mbufs from one pool, refcnt==1, etc.
So if it was me who confused you - I am sorry.
Konstantin

> Regards,

> Vadim.

> On Mar 23, 2015 8:44 PM, "Olivier MATZ" <olivier.matz@6wind.com> wrote:

> 

> > Hi Neil,

> >

> > On 03/19/2015 02:16 PM, Neil Horman wrote:

> > >> On 03/18/2015 09:58 PM, Neil Horman wrote:

> > >>>> +/**

> > >>>> + * Free a bulk of mbufs into its original mempool.

> > >>>> + * This function assumes:

> > >>>> + * - refcnt equals 1

> > >>>> + * - mbufs are direct

> > >>>> + * - all mbufs must belong to the same mempool

> > >>>> + *

> > >>>> + * @param mbufs

> > >>>> + *    Array of pointers to mbuf

> > >>>> + * @param count

> > >>>> + *    Array size

> > >>>> + */

> > >>>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,

> > >>>> +                                   unsigned count)

> > >>>> +{

> > >>>> +  unsigned idx;

> > >>>> +

> > >>>> +  RTE_MBUF_ASSERT(count > 0);

> > >>>> +

> > >>>> +  for (idx = 0; idx < count; idx++) {

> > >>>> +          RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);

> > >>>> +          RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);

> > >>>> +          rte_mbuf_refcnt_set(mbufs[idx], 0);

> > >>> This is really a misuse of the API.  The entire point of reference

> > counting is

> > >>> to know when an mbuf has no more references and can be freed.  By

> > forcing all

> > >>> the reference counts to zero here, you allow the refcnt infrastructure

> > to be

> > >>> circumvented, causing memory leaks.

> > >>>

> > >>> I think what you need to do here is enhance the underlying pktmbuf

> > interface

> > >>> such that an rte_mbuf structure has a destructor method association

> > with it

> > >>> which is called when its refcnt reaches zero.  That way the

> > >>> rte_pktmbuf_bulk_free function can just decrement the refcnt on each

> > >>> mbuf_structure, and the pool as a whole can be returned when the

> > destructor

> > >>> function discovers that all mbufs in that bulk pool are freed.

> > >>

> > >> I don't really understand what's the problem here. The API explicitly

> > >> describes the conditions for calling this functions: the segments are

> > >> directs, they belong to the same mempool, and their refcnt is 1.

> > >>

> > >> This function could be useful in a driver which knows that the mbuf

> > >> it allocated matches this conditions. I think an application that

> > >> only uses direct mbufs and one mempool could also use this function.

> > >

> > >

> > > That last condition is my issue with this patch, that the user has to

> > know what

> > > refcnts are.  It makes this api useful for little more than the test

> > case that

> > > is provided with it.  Its irritating enough that for singly allocated

> > mbufs the

> > > user has to know what the refcount of a buffer is before freeing, but at

> > least

> > > they can macrotize a {rte_pktmbuf_refcnt_update;

> > if(rte_pktmbuf_refct_read) then

> > > free} operation.

> > >

> > > With this, you've placed the user in charge of not only doing that, but

> > also of

> > > managing the relationship between pktmbufs and the pool they came from.

> > while

> > > that makes sense for the test case, it really doesn't in any general use

> > case in

> > > which packet processing is ever deferred or queued, because it means

> > that the

> > > application is now responsible for holding a pointer to every packet it

> > > allocates and checking its refcount periodically until it completes.

> > >

> > > There is never any reason that an application won't need to do this

> > management,

> > > so making it the purview of the application to handle rather than

> > properly

> > > integrating that functionality in the library is really a false savings.

> >

> > There are some places where you know that the prerequisites are met,

> > so you can save cycles by using this function.

> >

> > From what I imagine, if in a driver you allocate mbufs, chain them and

> > for some reason you realize you have to free them, you can use this

> > function instead of freeing them one by one.

> >

> > Also, as it's up to the application to decide how many mbuf pools are

> > created, and whether indirect mbufs are used or not, the application

> > can take the short path of using this function in some conditions.

> >

> > Vadim, maybe you have another reason or use case for adding this

> > function? Could you detail why you need it and how it improves your

> > use case?

> >

> > Regards,

> > Olivier

> >
  

Hi, Konstantin,

>Though from my point, such function should be generic as
rte_pktmbuf_free_chain() -
>no special limitations like all mbufs from one pool, refcnt==1, etc.
I misunderstood, I'll rework.
Regards,
 Vadim.

On Tue, Mar 24, 2015 at 1:48 AM, Ananyev, Konstantin <
konstantin.ananyev@intel.com> wrote:

> Hi Vadim,
>
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Vadim Suraev
> > Sent: Monday, March 23, 2015 5:31 PM
> > To: Olivier MATZ
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free
> functions added + unittest
> >
> > Hi, Olivier,
> > No, I personally need to free a chain using mempool bulk. If I'm not
> > mistaken, it has been proposed by one of reviewers to have lower level
> > function, so it was done (I'm sorry if misunderstood)
>
> Was it me?
> As I remember, I said it would be good to create rte_pktmbuf_bulk_free()
> or rte_pktmbuf_seg_bulk_free() -
> that would free a bulk of mbufs segments in the same manner as
> rte_pktmbuf_free_chain() does:
> count number of consecutive mbufs from the same mempool to be freed and
> then put them back into the pool at one go.
> Such function would be useful inside PMD code.
> In fact we already using analogy of such function inside vPMD TX code.
> Though from my point, such function should be generic as
> rte_pktmbuf_free_chain() -
> no special limitations like all mbufs from one pool, refcnt==1, etc.
> So if it was me who confused you - I am sorry.
> Konstantin
>
> > Regards,
> > Vadim.
> > On Mar 23, 2015 8:44 PM, "Olivier MATZ" <olivier.matz@6wind.com> wrote:
> >
> > > Hi Neil,
> > >
> > > On 03/19/2015 02:16 PM, Neil Horman wrote:
> > > >> On 03/18/2015 09:58 PM, Neil Horman wrote:
> > > >>>> +/**
> > > >>>> + * Free a bulk of mbufs into its original mempool.
> > > >>>> + * This function assumes:
> > > >>>> + * - refcnt equals 1
> > > >>>> + * - mbufs are direct
> > > >>>> + * - all mbufs must belong to the same mempool
> > > >>>> + *
> > > >>>> + * @param mbufs
> > > >>>> + *    Array of pointers to mbuf
> > > >>>> + * @param count
> > > >>>> + *    Array size
> > > >>>> + */
> > > >>>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> > > >>>> +                                   unsigned count)
> > > >>>> +{
> > > >>>> +  unsigned idx;
> > > >>>> +
> > > >>>> +  RTE_MBUF_ASSERT(count > 0);
> > > >>>> +
> > > >>>> +  for (idx = 0; idx < count; idx++) {
> > > >>>> +          RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> > > >>>> +          RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> > > >>>> +          rte_mbuf_refcnt_set(mbufs[idx], 0);
> > > >>> This is really a misuse of the API.  The entire point of reference
> > > counting is
> > > >>> to know when an mbuf has no more references and can be freed.  By
> > > forcing all
> > > >>> the reference counts to zero here, you allow the refcnt
> infrastructure
> > > to be
> > > >>> circumvented, causing memory leaks.
> > > >>>
> > > >>> I think what you need to do here is enhance the underlying pktmbuf
> > > interface
> > > >>> such that an rte_mbuf structure has a destructor method association
> > > with it
> > > >>> which is called when its refcnt reaches zero.  That way the
> > > >>> rte_pktmbuf_bulk_free function can just decrement the refcnt on
> each
> > > >>> mbuf_structure, and the pool as a whole can be returned when the
> > > destructor
> > > >>> function discovers that all mbufs in that bulk pool are freed.
> > > >>
> > > >> I don't really understand what's the problem here. The API
> explicitly
> > > >> describes the conditions for calling this functions: the segments
> are
> > > >> directs, they belong to the same mempool, and their refcnt is 1.
> > > >>
> > > >> This function could be useful in a driver which knows that the mbuf
> > > >> it allocated matches this conditions. I think an application that
> > > >> only uses direct mbufs and one mempool could also use this function.
> > > >
> > > >
> > > > That last condition is my issue with this patch, that the user has to
> > > know what
> > > > refcnts are.  It makes this api useful for little more than the test
> > > case that
> > > > is provided with it.  Its irritating enough that for singly allocated
> > > mbufs the
> > > > user has to know what the refcount of a buffer is before freeing,
> but at
> > > least
> > > > they can macrotize a {rte_pktmbuf_refcnt_update;
> > > if(rte_pktmbuf_refct_read) then
> > > > free} operation.
> > > >
> > > > With this, you've placed the user in charge of not only doing that,
> but
> > > also of
> > > > managing the relationship between pktmbufs and the pool they came
> from.
> > > while
> > > > that makes sense for the test case, it really doesn't in any general
> use
> > > case in
> > > > which packet processing is ever deferred or queued, because it means
> > > that the
> > > > application is now responsible for holding a pointer to every packet
> it
> > > > allocates and checking its refcount periodically until it completes.
> > > >
> > > > There is never any reason that an application won't need to do this
> > > management,
> > > > so making it the purview of the application to handle rather than
> > > properly
> > > > integrating that functionality in the library is really a false
> savings.
> > >
> > > There are some places where you know that the prerequisites are met,
> > > so you can save cycles by using this function.
> > >
> > > From what I imagine, if in a driver you allocate mbufs, chain them and
> > > for some reason you realize you have to free them, you can use this
> > > function instead of freeing them one by one.
> > >
> > > Also, as it's up to the application to decide how many mbuf pools are
> > > created, and whether indirect mbufs are used or not, the application
> > > can take the short path of using this function in some conditions.
> > >
> > > Vadim, maybe you have another reason or use case for adding this
> > > function? Could you detail why you need it and how it improves your
> > > use case?
> > >
> > > Regards,
> > > Olivier
> > >
>
  

Hi Vadim,
 
> From: Vadim Suraev [mailto:vadim.suraev@gmail.com]

> Sent: Tuesday, March 24, 2015 7:53 AM

> To: Ananyev, Konstantin

> Cc: Olivier MATZ; dev@dpdk.org

> Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest

> 

> Hi, Konstantin,

> 

> >Though from my point, such function should be generic as rte_pktmbuf_free_chain() -

> >no special limitations like all mbufs from one pool, refcnt==1, etc.

> I misunderstood, I'll rework.


Ok, thanks.
Konstantin

> Regards,

>  Vadim.

> 

> On Tue, Mar 24, 2015 at 1:48 AM, Ananyev, Konstantin <konstantin.ananyev@intel.com> wrote:

> Hi Vadim,

> 

> > -----Original Message-----

> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Vadim Suraev

> > Sent: Monday, March 23, 2015 5:31 PM

> > To: Olivier MATZ

> > Cc: dev@dpdk.org

> > Subject: Re: [dpdk-dev] [PATCH v2] rte_mbuf: mbuf bulk alloc/free functions added + unittest

> >

> > Hi, Olivier,

> > No, I personally need to free a chain using mempool bulk. If I'm not

> > mistaken, it has been proposed by one of reviewers to have lower level

> > function, so it was done (I'm sorry if misunderstood)

> 

> Was it me?

> As I remember, I said it would be good to create rte_pktmbuf_bulk_free() or rte_pktmbuf_seg_bulk_free() -

> that would free a bulk of mbufs segments in the same manner as rte_pktmbuf_free_chain() does:

> count number of consecutive mbufs from the same mempool to be freed and then put them back into the pool at one go.

> Such function would be useful inside PMD code.

> In fact we already using analogy of such function inside vPMD TX code.

> Though from my point, such function should be generic as rte_pktmbuf_free_chain() -

> no special limitations like all mbufs from one pool, refcnt==1, etc.

> So if it was me who confused you - I am sorry.

> Konstantin

> 

> > Regards,

> > Vadim.

> > On Mar 23, 2015 8:44 PM, "Olivier MATZ" <olivier.matz@6wind.com> wrote:

> >

> > > Hi Neil,

> > >

> > > On 03/19/2015 02:16 PM, Neil Horman wrote:

> > > >> On 03/18/2015 09:58 PM, Neil Horman wrote:

> > > >>>> +/**

> > > >>>> + * Free a bulk of mbufs into its original mempool.

> > > >>>> + * This function assumes:

> > > >>>> + * - refcnt equals 1

> > > >>>> + * - mbufs are direct

> > > >>>> + * - all mbufs must belong to the same mempool

> > > >>>> + *

> > > >>>> + * @param mbufs

> > > >>>> + *    Array of pointers to mbuf

> > > >>>> + * @param count

> > > >>>> + *    Array size

> > > >>>> + */

> > > >>>> +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,

> > > >>>> +                                   unsigned count)

> > > >>>> +{

> > > >>>> +  unsigned idx;

> > > >>>> +

> > > >>>> +  RTE_MBUF_ASSERT(count > 0);

> > > >>>> +

> > > >>>> +  for (idx = 0; idx < count; idx++) {

> > > >>>> +          RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);

> > > >>>> +          RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);

> > > >>>> +          rte_mbuf_refcnt_set(mbufs[idx], 0);

> > > >>> This is really a misuse of the API.  The entire point of reference

> > > counting is

> > > >>> to know when an mbuf has no more references and can be freed.  By

> > > forcing all

> > > >>> the reference counts to zero here, you allow the refcnt infrastructure

> > > to be

> > > >>> circumvented, causing memory leaks.

> > > >>>

> > > >>> I think what you need to do here is enhance the underlying pktmbuf

> > > interface

> > > >>> such that an rte_mbuf structure has a destructor method association

> > > with it

> > > >>> which is called when its refcnt reaches zero.  That way the

> > > >>> rte_pktmbuf_bulk_free function can just decrement the refcnt on each

> > > >>> mbuf_structure, and the pool as a whole can be returned when the

> > > destructor

> > > >>> function discovers that all mbufs in that bulk pool are freed.

> > > >>

> > > >> I don't really understand what's the problem here. The API explicitly

> > > >> describes the conditions for calling this functions: the segments are

> > > >> directs, they belong to the same mempool, and their refcnt is 1.

> > > >>

> > > >> This function could be useful in a driver which knows that the mbuf

> > > >> it allocated matches this conditions. I think an application that

> > > >> only uses direct mbufs and one mempool could also use this function.

> > > >

> > > >

> > > > That last condition is my issue with this patch, that the user has to

> > > know what

> > > > refcnts are.  It makes this api useful for little more than the test

> > > case that

> > > > is provided with it.  Its irritating enough that for singly allocated

> > > mbufs the

> > > > user has to know what the refcount of a buffer is before freeing, but at

> > > least

> > > > they can macrotize a {rte_pktmbuf_refcnt_update;

> > > if(rte_pktmbuf_refct_read) then

> > > > free} operation.

> > > >

> > > > With this, you've placed the user in charge of not only doing that, but

> > > also of

> > > > managing the relationship between pktmbufs and the pool they came from.

> > > while

> > > > that makes sense for the test case, it really doesn't in any general use

> > > case in

> > > > which packet processing is ever deferred or queued, because it means

> > > that the

> > > > application is now responsible for holding a pointer to every packet it

> > > > allocates and checking its refcount periodically until it completes.

> > > >

> > > > There is never any reason that an application won't need to do this

> > > management,

> > > > so making it the purview of the application to handle rather than

> > > properly

> > > > integrating that functionality in the library is really a false savings.

> > >

> > > There are some places where you know that the prerequisites are met,

> > > so you can save cycles by using this function.

> > >

> > > From what I imagine, if in a driver you allocate mbufs, chain them and

> > > for some reason you realize you have to free them, you can use this

> > > function instead of freeing them one by one.

> > >

> > > Also, as it's up to the application to decide how many mbuf pools are

> > > created, and whether indirect mbufs are used or not, the application

> > > can take the short path of using this function in some conditions.

> > >

> > > Vadim, maybe you have another reason or use case for adding this

> > > function? Could you detail why you need it and how it improves your

> > > use case?

> > >

> > > Regards,

> > > Olivier

> > >
  

Hi, Neil

>I think what you need to do here is enhance the underlying pktmbuf
interface
>such that an rte_mbuf structure has a destructor method association with it
>which is called when its refcnt reaches zero.  That way the
>rte_pktmbuf_bulk_free function can just decrement the refcnt on each
>mbuf_structure, and the pool as a whole can be returned when the destructor
>function discovers that all mbufs in that bulk pool are freed.

I thought again and it looks to me that if mempool_cache is enabled,
rte_pktmbuf_bulk_free and  are redundant because the logic would be very
similar to already implemented in rte_mempool. Probably the only
rte_pktmbuf_alloc_bulk makes sense in this patch?

Regards,
 Vadim.

On Wed, Mar 18, 2015 at 10:58 PM, Neil Horman <nhorman@tuxdriver.com> wrote:

> On Wed, Mar 18, 2015 at 10:21:18PM +0200, vadim.suraev@gmail.com wrote:
> > From: "vadim.suraev@gmail.com" <vadim.suraev@gmail.com>
> >
> > This patch adds mbuf bulk allocation/freeing functions and unittest
> >
> > Signed-off-by: Vadim Suraev
> > <vadim.suraev@gmail.com>
> > ---
> > New in v2:
> >     - function rte_pktmbuf_alloc_bulk added
> >     - function rte_pktmbuf_bulk_free added
> >     - function rte_pktmbuf_free_chain added
> >     - applied reviewers' comments
> >
> >  app/test/test_mbuf.c       |   94
> +++++++++++++++++++++++++++++++++++++++++++-
> >  lib/librte_mbuf/rte_mbuf.h |   91
> ++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 184 insertions(+), 1 deletion(-)
> >
> > diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
> > index 1ff66cb..b20c6a4 100644
> > --- a/app/test/test_mbuf.c
> > +++ b/app/test/test_mbuf.c
> > @@ -77,6 +77,7 @@
> >  #define REFCNT_RING_SIZE        (REFCNT_MBUF_NUM * REFCNT_MAX_REF)
> >
> >  #define MAKE_STRING(x)          # x
> > +#define MBUF_POOL_LOCAL_CACHE_SIZE 32
> >
> >  static struct rte_mempool *pktmbuf_pool = NULL;
> >
> > @@ -405,6 +406,84 @@ test_pktmbuf_pool(void)
> >       return ret;
> >  }
> >
> ><snip>
> > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > index 17ba791..fabeae2 100644
> > --- a/lib/librte_mbuf/rte_mbuf.h
> > +++ b/lib/librte_mbuf/rte_mbuf.h
> > @@ -825,6 +825,97 @@ static inline void rte_pktmbuf_free(struct rte_mbuf
> *m)
> >  }
> >
> >  /**
> > + * Allocate a bulk of mbufs, initiate refcnt and resets
> > + *
> > + * @param pool
> > + *    memory pool to allocate from
> > + * @param mbufs
> > + *    Array of pointers to mbuf
> > + * @param count
> > + *    Array size
> > + */
> > +static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool,
> > +                                      struct rte_mbuf **mbufs,
> > +                                      unsigned count)
> > +{
> > +     unsigned idx;
> > +     int rc = 0;
> > +
> > +     rc = rte_mempool_get_bulk(pool, (void **)mbufs, count);
> > +     if (unlikely(rc))
> > +             return rc;
> > +
> > +     for (idx = 0; idx < count; idx++) {
> > +             RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
> > +             rte_mbuf_refcnt_set(mbufs[idx], 1);
> > +             rte_pktmbuf_reset(mbufs[idx]);
> > +     }
> > +     return rc;
> > +}
> > +
> > +/**
> > + * Free a bulk of mbufs into its original mempool.
> > + * This function assumes:
> > + * - refcnt equals 1
> > + * - mbufs are direct
> > + * - all mbufs must belong to the same mempool
> > + *
> > + * @param mbufs
> > + *    Array of pointers to mbuf
> > + * @param count
> > + *    Array size
> > + */
> > +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> > +                                      unsigned count)
> > +{
> > +     unsigned idx;
> > +
> > +     RTE_MBUF_ASSERT(count > 0);
> > +
> > +     for (idx = 0; idx < count; idx++) {
> > +             RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> > +             RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> > +             rte_mbuf_refcnt_set(mbufs[idx], 0);
> This is really a misuse of the API.  The entire point of reference
> counting is
> to know when an mbuf has no more references and can be freed.  By forcing
> all
> the reference counts to zero here, you allow the refcnt infrastructure to
> be
> circumvented, causing memory leaks.
>
> I think what you need to do here is enhance the underlying pktmbuf
> interface
> such that an rte_mbuf structure has a destructor method association with it
> which is called when its refcnt reaches zero.  That way the
> rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> mbuf_structure, and the pool as a whole can be returned when the destructor
> function discovers that all mbufs in that bulk pool are freed.
>
> Neil
>
>
  

On Mon, Mar 30, 2015 at 10:04:20PM +0300, Vadim Suraev wrote:
> Hi, Neil
> 
> >I think what you need to do here is enhance the underlying pktmbuf
> interface
> >such that an rte_mbuf structure has a destructor method association with it
> >which is called when its refcnt reaches zero.  That way the
> >rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> >mbuf_structure, and the pool as a whole can be returned when the destructor
> >function discovers that all mbufs in that bulk pool are freed.
> 
> I thought again and it looks to me that if mempool_cache is enabled,
> rte_pktmbuf_bulk_free and  are redundant because the logic would be very
> similar to already implemented in rte_mempool. Probably the only
> rte_pktmbuf_alloc_bulk makes sense in this patch?
> 
> Regards,
>  Vadim.
> 
Looking at it, yes, I agree, using an externally allocated large contiguous
block of memory, mapped with rte_mempool_xmem_create, then allocating with
rte_pktmbuf_alloc would likely work in exactly the same way.  I'd argue that
even the bulk alloc function isn't really needed, as its implementation seems
like it would just be a for loop with 2-3 lines in it.

Neil

> On Wed, Mar 18, 2015 at 10:58 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
> 
> > On Wed, Mar 18, 2015 at 10:21:18PM +0200, vadim.suraev@gmail.com wrote:
> > > From: "vadim.suraev@gmail.com" <vadim.suraev@gmail.com>
> > >
> > > This patch adds mbuf bulk allocation/freeing functions and unittest
> > >
> > > Signed-off-by: Vadim Suraev
> > > <vadim.suraev@gmail.com>
> > > ---
> > > New in v2:
> > >     - function rte_pktmbuf_alloc_bulk added
> > >     - function rte_pktmbuf_bulk_free added
> > >     - function rte_pktmbuf_free_chain added
> > >     - applied reviewers' comments
> > >
> > >  app/test/test_mbuf.c       |   94
> > +++++++++++++++++++++++++++++++++++++++++++-
> > >  lib/librte_mbuf/rte_mbuf.h |   91
> > ++++++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 184 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
> > > index 1ff66cb..b20c6a4 100644
> > > --- a/app/test/test_mbuf.c
> > > +++ b/app/test/test_mbuf.c
> > > @@ -77,6 +77,7 @@
> > >  #define REFCNT_RING_SIZE        (REFCNT_MBUF_NUM * REFCNT_MAX_REF)
> > >
> > >  #define MAKE_STRING(x)          # x
> > > +#define MBUF_POOL_LOCAL_CACHE_SIZE 32
> > >
> > >  static struct rte_mempool *pktmbuf_pool = NULL;
> > >
> > > @@ -405,6 +406,84 @@ test_pktmbuf_pool(void)
> > >       return ret;
> > >  }
> > >
> > ><snip>
> > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > > index 17ba791..fabeae2 100644
> > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > @@ -825,6 +825,97 @@ static inline void rte_pktmbuf_free(struct rte_mbuf
> > *m)
> > >  }
> > >
> > >  /**
> > > + * Allocate a bulk of mbufs, initiate refcnt and resets
> > > + *
> > > + * @param pool
> > > + *    memory pool to allocate from
> > > + * @param mbufs
> > > + *    Array of pointers to mbuf
> > > + * @param count
> > > + *    Array size
> > > + */
> > > +static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool,
> > > +                                      struct rte_mbuf **mbufs,
> > > +                                      unsigned count)
> > > +{
> > > +     unsigned idx;
> > > +     int rc = 0;
> > > +
> > > +     rc = rte_mempool_get_bulk(pool, (void **)mbufs, count);
> > > +     if (unlikely(rc))
> > > +             return rc;
> > > +
> > > +     for (idx = 0; idx < count; idx++) {
> > > +             RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
> > > +             rte_mbuf_refcnt_set(mbufs[idx], 1);
> > > +             rte_pktmbuf_reset(mbufs[idx]);
> > > +     }
> > > +     return rc;
> > > +}
> > > +
> > > +/**
> > > + * Free a bulk of mbufs into its original mempool.
> > > + * This function assumes:
> > > + * - refcnt equals 1
> > > + * - mbufs are direct
> > > + * - all mbufs must belong to the same mempool
> > > + *
> > > + * @param mbufs
> > > + *    Array of pointers to mbuf
> > > + * @param count
> > > + *    Array size
> > > + */
> > > +static inline void rte_pktmbuf_bulk_free(struct rte_mbuf **mbufs,
> > > +                                      unsigned count)
> > > +{
> > > +     unsigned idx;
> > > +
> > > +     RTE_MBUF_ASSERT(count > 0);
> > > +
> > > +     for (idx = 0; idx < count; idx++) {
> > > +             RTE_MBUF_ASSERT(mbufs[idx]->pool == mbufs[0]->pool);
> > > +             RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 1);
> > > +             rte_mbuf_refcnt_set(mbufs[idx], 0);
> > This is really a misuse of the API.  The entire point of reference
> > counting is
> > to know when an mbuf has no more references and can be freed.  By forcing
> > all
> > the reference counts to zero here, you allow the refcnt infrastructure to
> > be
> > circumvented, causing memory leaks.
> >
> > I think what you need to do here is enhance the underlying pktmbuf
> > interface
> > such that an rte_mbuf structure has a destructor method association with it
> > which is called when its refcnt reaches zero.  That way the
> > rte_pktmbuf_bulk_free function can just decrement the refcnt on each
> > mbuf_structure, and the pool as a whole can be returned when the destructor
> > function discovers that all mbufs in that bulk pool are freed.
> >
> > Neil
> >
> >