[dpdk-dev] mbuf: optimize first reference increment in rte_pktmbuf_attach
Commit Message
As it's done in __rte_pktmbuf_prefree_seg(), we can avoid using an
atomic increment in rte_pktmbuf_attach() by checking if we are the
only owner of the mbuf first.
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
---
lib/librte_mbuf/rte_mbuf.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
Comments
On Mon, Jun 01, 2015 at 11:32:25AM +0200, Olivier Matz wrote:
> As it's done in __rte_pktmbuf_prefree_seg(), we can avoid using an
> atomic increment in rte_pktmbuf_attach() by checking if we are the
> only owner of the mbuf first.
>
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
> lib/librte_mbuf/rte_mbuf.h | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index ab6de67..cea35b7 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -838,7 +838,11 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *m)
> else
> md = rte_mbuf_from_indirect(m);
>
> - rte_mbuf_refcnt_update(md, 1);
> + /* optimize the case where we are the only owner */
> + if (likely(rte_mbuf_refcnt_read(md) == 1))
> + rte_mbuf_refcnt_set(md, 2);
> + else
> + rte_mbuf_refcnt_update(md, 1);
> mi->priv_size = m->priv_size;
> mi->buf_physaddr = m->buf_physaddr;
> mi->buf_addr = m->buf_addr;
> --
> 2.1.4
>
Why not make the change inside rte_mbuf_refcnt_update itself? If it is ever
called with a current refcnt of 1, it should always be safe to do the update
without a cmpset.
/Bruce
Hi Bruce,
On 06/03/2015 12:59 PM, Bruce Richardson wrote:
> On Mon, Jun 01, 2015 at 11:32:25AM +0200, Olivier Matz wrote:
>> As it's done in __rte_pktmbuf_prefree_seg(), we can avoid using an
>> atomic increment in rte_pktmbuf_attach() by checking if we are the
>> only owner of the mbuf first.
>>
>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>> ---
>> lib/librte_mbuf/rte_mbuf.h | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
>> index ab6de67..cea35b7 100644
>> --- a/lib/librte_mbuf/rte_mbuf.h
>> +++ b/lib/librte_mbuf/rte_mbuf.h
>> @@ -838,7 +838,11 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *m)
>> else
>> md = rte_mbuf_from_indirect(m);
>>
>> - rte_mbuf_refcnt_update(md, 1);
>> + /* optimize the case where we are the only owner */
>> + if (likely(rte_mbuf_refcnt_read(md) == 1))
>> + rte_mbuf_refcnt_set(md, 2);
>> + else
>> + rte_mbuf_refcnt_update(md, 1);
>> mi->priv_size = m->priv_size;
>> mi->buf_physaddr = m->buf_physaddr;
>> mi->buf_addr = m->buf_addr;
>> --
>> 2.1.4
>>
> Why not make the change inside rte_mbuf_refcnt_update itself? If it is ever
> called with a current refcnt of 1, it should always be safe to do the update
> without a cmpset.
Good idea, I'll see if I can do that in a new version.
Thanks,
Olivier
>
> /Bruce
>
@@ -838,7 +838,11 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *m)
else
md = rte_mbuf_from_indirect(m);
- rte_mbuf_refcnt_update(md, 1);
+ /* optimize the case where we are the only owner */
+ if (likely(rte_mbuf_refcnt_read(md) == 1))
+ rte_mbuf_refcnt_set(md, 2);
+ else
+ rte_mbuf_refcnt_update(md, 1);
mi->priv_size = m->priv_size;
mi->buf_physaddr = m->buf_physaddr;
mi->buf_addr = m->buf_addr;