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[RFC,0/2] add Tx prepare support for bonding device

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Series add Tx prepare support for bonding device | expand

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Chengchang Tang April 16, 2021, 11:04 a.m. UTC
This patch add Tx prepare for bonding device.

Currently, the bonding driver has not implemented the callback of
rte_eth_tx_prepare function. Therefore, the TX prepare function of the
slave devices will never be invoked. When hardware offloading such as
CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
to adjust packets (for example, set correct pseudo packet headers).
Otherwise, related offloading fails and even packets are sent
incorrectly. Due to this limitation, the bonded device cannot use these
HW offloading in the Tx direction.

Because packet sending algorithms are numerous and complex in bond PMD,
it is hard to design the callback for rte_eth_tx_prepare. In this patch,
the tx_prepare callback of bonding PMD is not implemented. Instead,
rte_eth_tx_prepare has been called in tx_burst callback. And a global
variable is introduced to control whether the bonded device need call
the rte_eth_tx_prepare. If upper-layer users need to use some TX
offloading that depend on tx_prepare , they should enable the preparation
function. In this way, the bonded device will call the rte_eth_tx_prepare
for the fast path packets in the tx_burst callback.

Chengchang Tang (2):
  net/bonding: add Tx prepare for bonding
  app/testpmd: add cmd for bonding Tx prepare

 app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
 doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
 drivers/net/bonding/eth_bond_private.h      |  1 +
 drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
 drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
 drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
 drivers/net/bonding/version.map             |  5 +++
 7 files changed, 167 insertions(+), 4 deletions(-)

--
2.7.4

Comments

Min Hu (Connor) April 16, 2021, 11:12 a.m. UTC | #1
Looks good to me.

在 2021/4/16 19:04, Chengchang Tang 写道:
> This patch add Tx prepare for bonding device.
> 
> Currently, the bonding driver has not implemented the callback of
> rte_eth_tx_prepare function. Therefore, the TX prepare function of the
> slave devices will never be invoked. When hardware offloading such as
> CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
> to adjust packets (for example, set correct pseudo packet headers).
> Otherwise, related offloading fails and even packets are sent
> incorrectly. Due to this limitation, the bonded device cannot use these
> HW offloading in the Tx direction.
> 
> Because packet sending algorithms are numerous and complex in bond PMD,
> it is hard to design the callback for rte_eth_tx_prepare. In this patch,
> the tx_prepare callback of bonding PMD is not implemented. Instead,
> rte_eth_tx_prepare has been called in tx_burst callback. And a global
> variable is introduced to control whether the bonded device need call
> the rte_eth_tx_prepare. If upper-layer users need to use some TX
> offloading that depend on tx_prepare , they should enable the preparation
> function. In this way, the bonded device will call the rte_eth_tx_prepare
> for the fast path packets in the tx_burst callback.
> 
> Chengchang Tang (2):
>    net/bonding: add Tx prepare for bonding
>    app/testpmd: add cmd for bonding Tx prepare
> 
>   app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
>   doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
>   drivers/net/bonding/eth_bond_private.h      |  1 +
>   drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
>   drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
>   drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
>   drivers/net/bonding/version.map             |  5 +++
>   7 files changed, 167 insertions(+), 4 deletions(-)
> 
> --
> 2.7.4
> 
> .
>
Ferruh Yigit April 20, 2021, 1:26 a.m. UTC | #2
On 4/16/2021 12:04 PM, Chengchang Tang wrote:
> This patch add Tx prepare for bonding device.
> 
> Currently, the bonding driver has not implemented the callback of
> rte_eth_tx_prepare function. Therefore, the TX prepare function of the
> slave devices will never be invoked. When hardware offloading such as
> CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
> to adjust packets (for example, set correct pseudo packet headers).
> Otherwise, related offloading fails and even packets are sent
> incorrectly. Due to this limitation, the bonded device cannot use these
> HW offloading in the Tx direction.
> 
> Because packet sending algorithms are numerous and complex in bond PMD,
> it is hard to design the callback for rte_eth_tx_prepare. In this patch,
> the tx_prepare callback of bonding PMD is not implemented. Instead,
> rte_eth_tx_prepare has been called in tx_burst callback. And a global
> variable is introduced to control whether the bonded device need call
> the rte_eth_tx_prepare. If upper-layer users need to use some TX
> offloading that depend on tx_prepare , they should enable the preparation
> function. In this way, the bonded device will call the rte_eth_tx_prepare
> for the fast path packets in the tx_burst callback.
> 

What do you think to add a devarg to bonding PMD to control the tx_prepare?
It won't be as dynamic as API, since it can be possible to change the behavior 
after application is started with API, but do we really need this?

> Chengchang Tang (2):
>    net/bonding: add Tx prepare for bonding
>    app/testpmd: add cmd for bonding Tx prepare
> 
>   app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
>   doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
>   drivers/net/bonding/eth_bond_private.h      |  1 +
>   drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
>   drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
>   drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
>   drivers/net/bonding/version.map             |  5 +++
>   7 files changed, 167 insertions(+), 4 deletions(-)
> 
> --
> 2.7.4
>
Chengchang Tang April 20, 2021, 2:44 a.m. UTC | #3
On 2021/4/20 9:26, Ferruh Yigit wrote:
> On 4/16/2021 12:04 PM, Chengchang Tang wrote:
>> This patch add Tx prepare for bonding device.
>>
>> Currently, the bonding driver has not implemented the callback of
>> rte_eth_tx_prepare function. Therefore, the TX prepare function of the
>> slave devices will never be invoked. When hardware offloading such as
>> CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
>> to adjust packets (for example, set correct pseudo packet headers).
>> Otherwise, related offloading fails and even packets are sent
>> incorrectly. Due to this limitation, the bonded device cannot use these
>> HW offloading in the Tx direction.
>>
>> Because packet sending algorithms are numerous and complex in bond PMD,
>> it is hard to design the callback for rte_eth_tx_prepare. In this patch,
>> the tx_prepare callback of bonding PMD is not implemented. Instead,
>> rte_eth_tx_prepare has been called in tx_burst callback. And a global
>> variable is introduced to control whether the bonded device need call
>> the rte_eth_tx_prepare. If upper-layer users need to use some TX
>> offloading that depend on tx_prepare , they should enable the preparation
>> function. In this way, the bonded device will call the rte_eth_tx_prepare
>> for the fast path packets in the tx_burst callback.
>>
> 
> What do you think to add a devarg to bonding PMD to control the tx_prepare?
> It won't be as dynamic as API, since it can be possible to change the behavior after application is started with API, but do we really need this?

If an API is not added, unnecessary constraints may be introduced. If the
bonding device is created through the rte_eth_bond_create interface instead
devarg "vdev", this function cannot be used because devargs does not take effect
in this case. But from an ease-of-use perspective, adding a devarg is a good
idea. I will add related implementations in the later official patches.

If I understand correctly, the current community does not want to introduce
more private APIs for PMDs. However, the absence of an API on this issue would
introduce some unnecessary constraints, and from that point of view, I think
adding an API seems necessary.
> 
>> Chengchang Tang (2):
>>    net/bonding: add Tx prepare for bonding
>>    app/testpmd: add cmd for bonding Tx prepare
>>
>>   app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
>>   doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
>>   drivers/net/bonding/eth_bond_private.h      |  1 +
>>   drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
>>   drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
>>   drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
>>   drivers/net/bonding/version.map             |  5 +++
>>   7 files changed, 167 insertions(+), 4 deletions(-)
>>
>> -- 
>> 2.7.4
>>
> 
> 
> .
>
Ananyev, Konstantin April 20, 2021, 8:33 a.m. UTC | #4
Hi everyone,

> 
> On 2021/4/20 9:26, Ferruh Yigit wrote:
> > On 4/16/2021 12:04 PM, Chengchang Tang wrote:
> >> This patch add Tx prepare for bonding device.
> >>
> >> Currently, the bonding driver has not implemented the callback of
> >> rte_eth_tx_prepare function. Therefore, the TX prepare function of the
> >> slave devices will never be invoked. When hardware offloading such as
> >> CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
> >> to adjust packets (for example, set correct pseudo packet headers).
> >> Otherwise, related offloading fails and even packets are sent
> >> incorrectly. Due to this limitation, the bonded device cannot use these
> >> HW offloading in the Tx direction.
> >>
> >> Because packet sending algorithms are numerous and complex in bond PMD,
> >> it is hard to design the callback for rte_eth_tx_prepare. In this patch,
> >> the tx_prepare callback of bonding PMD is not implemented. Instead,
> >> rte_eth_tx_prepare has been called in tx_burst callback. And a global
> >> variable is introduced to control whether the bonded device need call
> >> the rte_eth_tx_prepare. If upper-layer users need to use some TX
> >> offloading that depend on tx_prepare , they should enable the preparation
> >> function. In this way, the bonded device will call the rte_eth_tx_prepare
> >> for the fast path packets in the tx_burst callback.

I admit that I didn't look at the implementation yet, but it sounds like 
overcomplication to me. Can't we just have a new TX function for bonding PMD
when TX offloads are enabled? And inside that function we will do:
tx_prepare(); tx_burst(); for selected device.
We can select this function at setup stage analysing requested by user TX offloads. 


> >>
> >
> > What do you think to add a devarg to bonding PMD to control the tx_prepare?
> > It won't be as dynamic as API, since it can be possible to change the behavior after application is started with API, but do we really need
> this?
> 
> If an API is not added, unnecessary constraints may be introduced. If the
> bonding device is created through the rte_eth_bond_create interface instead
> devarg "vdev", this function cannot be used because devargs does not take effect
> in this case. But from an ease-of-use perspective, adding a devarg is a good
> idea. I will add related implementations in the later official patches.

I am also against introducing new devarg to control tx_prepare() invocation.
I think at dev_config/queue_setup phase PMD will have enough information to decide.

> 
> If I understand correctly, the current community does not want to introduce
> more private APIs for PMDs. However, the absence of an API on this issue would
> introduce some unnecessary constraints, and from that point of view, I think
> adding an API seems necessary.
> >
> >> Chengchang Tang (2):
> >>    net/bonding: add Tx prepare for bonding
> >>    app/testpmd: add cmd for bonding Tx prepare
> >>
> >>   app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
> >>   doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
> >>   drivers/net/bonding/eth_bond_private.h      |  1 +
> >>   drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
> >>   drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
> >>   drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
> >>   drivers/net/bonding/version.map             |  5 +++
> >>   7 files changed, 167 insertions(+), 4 deletions(-)
> >>
> >> --
> >> 2.7.4
> >>
> >
> >
> > .
> >
Chengchang Tang April 20, 2021, 12:44 p.m. UTC | #5
Hi
On 2021/4/20 16:33, Ananyev, Konstantin wrote:
> Hi everyone,
> 
>>
>> On 2021/4/20 9:26, Ferruh Yigit wrote:
>>> On 4/16/2021 12:04 PM, Chengchang Tang wrote:
>>>> This patch add Tx prepare for bonding device.
>>>>
>>>> Currently, the bonding driver has not implemented the callback of
>>>> rte_eth_tx_prepare function. Therefore, the TX prepare function of the
>>>> slave devices will never be invoked. When hardware offloading such as
>>>> CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
>>>> to adjust packets (for example, set correct pseudo packet headers).
>>>> Otherwise, related offloading fails and even packets are sent
>>>> incorrectly. Due to this limitation, the bonded device cannot use these
>>>> HW offloading in the Tx direction.
>>>>
>>>> Because packet sending algorithms are numerous and complex in bond PMD,
>>>> it is hard to design the callback for rte_eth_tx_prepare. In this patch,
>>>> the tx_prepare callback of bonding PMD is not implemented. Instead,
>>>> rte_eth_tx_prepare has been called in tx_burst callback. And a global
>>>> variable is introduced to control whether the bonded device need call
>>>> the rte_eth_tx_prepare. If upper-layer users need to use some TX
>>>> offloading that depend on tx_prepare , they should enable the preparation
>>>> function. In this way, the bonded device will call the rte_eth_tx_prepare
>>>> for the fast path packets in the tx_burst callback.
> 
> I admit that I didn't look at the implementation yet, but it sounds like 
> overcomplication to me. Can't we just have a new TX function for bonding PMD
> when TX offloads are enabled? And inside that function we will do:
> tx_prepare(); tx_burst(); for selected device.

The solution you mentioned is workable and may perform better. However, the current
solution is also simple and has a limited impact on performance. It is actually:
if (tx_prepare_enable)
	tx_prepare();
tx_burst();

Overall, it adds almost only one judgment to the case where the related Tx offloads
is not turned on.

> We can select this function at setup stage analysing requested by user TX offloads. 
> 

In PMDs, it is a common practice to select different Tx/Rx function during the setup
phase. But for a 'vdev' device like Bonding, we may need to think more about it.
The reasons are explained below.
> 
>>>>
>>>
>>> What do you think to add a devarg to bonding PMD to control the tx_prepare?
>>> It won't be as dynamic as API, since it can be possible to change the behavior after application is started with API, but do we really need
>> this?
>>
>> If an API is not added, unnecessary constraints may be introduced. If the
>> bonding device is created through the rte_eth_bond_create interface instead
>> devarg "vdev", this function cannot be used because devargs does not take effect
>> in this case. But from an ease-of-use perspective, adding a devarg is a good
>> idea. I will add related implementations in the later official patches.
> 
> I am also against introducing new devarg to control tx_prepare() invocation.
> I think at dev_config/queue_setup phase PMD will have enough information to decide.
> 
Currently, the community does not specify which Tx offloads need to invoke tx_prepare.
For Vdev devices such as bond, all NIC devices need to be considered. Generally,
tx_prepare is used in CKSUM and TSO. It is possible that for some NIC devices, even
CKSUM and TSO do not need to invoke tx_prepare, or for some NIC devices, there are
other Tx offloads that need to call tx_prepare. From this perspective, leaving the
choice to the user seems to be a better choice.
>>
>> If I understand correctly, the current community does not want to introduce
>> more private APIs for PMDs. However, the absence of an API on this issue would
>> introduce some unnecessary constraints, and from that point of view, I think
>> adding an API seems necessary.
>>>
>>>> Chengchang Tang (2):
>>>>    net/bonding: add Tx prepare for bonding
>>>>    app/testpmd: add cmd for bonding Tx prepare
>>>>
>>>>   app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
>>>>   doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
>>>>   drivers/net/bonding/eth_bond_private.h      |  1 +
>>>>   drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
>>>>   drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
>>>>   drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
>>>>   drivers/net/bonding/version.map             |  5 +++
>>>>   7 files changed, 167 insertions(+), 4 deletions(-)
>>>>
>>>> --
>>>> 2.7.4
>>>>
>>>
>>>
>>> .
>>>
>
Ananyev, Konstantin April 20, 2021, 1:18 p.m. UTC | #6
> -----Original Message-----
> From: Chengchang Tang <tangchengchang@huawei.com>
> Sent: Tuesday, April 20, 2021 1:44 PM
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>; dev@dpdk.org
> Cc: linuxarm@huawei.com; chas3@att.com; humin29@huawei.com
> Subject: Re: [dpdk-dev] [RFC 0/2] add Tx prepare support for bonding device
> 
> Hi
> On 2021/4/20 16:33, Ananyev, Konstantin wrote:
> > Hi everyone,
> >
> >>
> >> On 2021/4/20 9:26, Ferruh Yigit wrote:
> >>> On 4/16/2021 12:04 PM, Chengchang Tang wrote:
> >>>> This patch add Tx prepare for bonding device.
> >>>>
> >>>> Currently, the bonding driver has not implemented the callback of
> >>>> rte_eth_tx_prepare function. Therefore, the TX prepare function of the
> >>>> slave devices will never be invoked. When hardware offloading such as
> >>>> CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
> >>>> to adjust packets (for example, set correct pseudo packet headers).
> >>>> Otherwise, related offloading fails and even packets are sent
> >>>> incorrectly. Due to this limitation, the bonded device cannot use these
> >>>> HW offloading in the Tx direction.
> >>>>
> >>>> Because packet sending algorithms are numerous and complex in bond PMD,
> >>>> it is hard to design the callback for rte_eth_tx_prepare. In this patch,
> >>>> the tx_prepare callback of bonding PMD is not implemented. Instead,
> >>>> rte_eth_tx_prepare has been called in tx_burst callback. And a global
> >>>> variable is introduced to control whether the bonded device need call
> >>>> the rte_eth_tx_prepare. If upper-layer users need to use some TX
> >>>> offloading that depend on tx_prepare , they should enable the preparation
> >>>> function. In this way, the bonded device will call the rte_eth_tx_prepare
> >>>> for the fast path packets in the tx_burst callback.
> >
> > I admit that I didn't look at the implementation yet, but it sounds like
> > overcomplication to me. Can't we just have a new TX function for bonding PMD
> > when TX offloads are enabled? And inside that function we will do:
> > tx_prepare(); tx_burst(); for selected device.
> 
> The solution you mentioned is workable and may perform better. However, the current
> solution is also simple and has a limited impact on performance. It is actually:
> if (tx_prepare_enable)
> 	tx_prepare();
> tx_burst();
> 
> Overall, it adds almost only one judgment to the case where the related Tx offloads
> is not turned on.
> 
> > We can select this function at setup stage analysing requested by user TX offloads.
> >
> 
> In PMDs, it is a common practice to select different Tx/Rx function during the setup
> phase. But for a 'vdev' device like Bonding, we may need to think more about it.
> The reasons are explained below.
> >
> >>>>
> >>>
> >>> What do you think to add a devarg to bonding PMD to control the tx_prepare?
> >>> It won't be as dynamic as API, since it can be possible to change the behavior after application is started with API, but do we really need
> >> this?
> >>
> >> If an API is not added, unnecessary constraints may be introduced. If the
> >> bonding device is created through the rte_eth_bond_create interface instead
> >> devarg "vdev", this function cannot be used because devargs does not take effect
> >> in this case. But from an ease-of-use perspective, adding a devarg is a good
> >> idea. I will add related implementations in the later official patches.
> >
> > I am also against introducing new devarg to control tx_prepare() invocation.
> > I think at dev_config/queue_setup phase PMD will have enough information to decide.
> >
> Currently, the community does not specify which Tx offloads need to invoke tx_prepare.

I think inside bond PMD we can safely assume that any TX offload does need tx_prepare().
If that's not the case then slave dev tx_prepare pointer will be NULL and rte_eth_tx_prepare()
will be just a NOOP. 

> For Vdev devices such as bond, all NIC devices need to be considered. Generally,
> tx_prepare is used in CKSUM and TSO. It is possible that for some NIC devices, even
> CKSUM and TSO do not need to invoke tx_prepare, or for some NIC devices, there are
> other Tx offloads that need to call tx_prepare. From this perspective, leaving the
> choice to the user seems to be a better choice.

Wonder how user will know when to enable/disable it?
As you said it depends on the underlying HW/PMD and can change from system to system?
I think it is PMD that needs to take this decision, and I think the safest bet might be to enable
it when any TX offloads was enabled by user.

> >>
> >> If I understand correctly, the current community does not want to introduce
> >> more private APIs for PMDs. However, the absence of an API on this issue would
> >> introduce some unnecessary constraints, and from that point of view, I think
> >> adding an API seems necessary.
> >>>
> >>>> Chengchang Tang (2):
> >>>>    net/bonding: add Tx prepare for bonding
> >>>>    app/testpmd: add cmd for bonding Tx prepare
> >>>>
> >>>>   app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
> >>>>   doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
> >>>>   drivers/net/bonding/eth_bond_private.h      |  1 +
> >>>>   drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
> >>>>   drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
> >>>>   drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
> >>>>   drivers/net/bonding/version.map             |  5 +++
> >>>>   7 files changed, 167 insertions(+), 4 deletions(-)
> >>>>
> >>>> --
> >>>> 2.7.4
> >>>>
> >>>
> >>>
> >>> .
> >>>
> >
Chengchang Tang April 20, 2021, 2:06 p.m. UTC | #7
On 2021/4/20 21:18, Ananyev, Konstantin wrote:
> 
> 
>> -----Original Message-----
>> From: Chengchang Tang <tangchengchang@huawei.com>
>> Sent: Tuesday, April 20, 2021 1:44 PM
>> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>; dev@dpdk.org
>> Cc: linuxarm@huawei.com; chas3@att.com; humin29@huawei.com
>> Subject: Re: [dpdk-dev] [RFC 0/2] add Tx prepare support for bonding device
>>
>> Hi
>> On 2021/4/20 16:33, Ananyev, Konstantin wrote:
>>> Hi everyone,
>>>
>>>>
>>>> On 2021/4/20 9:26, Ferruh Yigit wrote:
>>>>> On 4/16/2021 12:04 PM, Chengchang Tang wrote:
>>>>>> This patch add Tx prepare for bonding device.
>>>>>>
>>>>>> Currently, the bonding driver has not implemented the callback of
>>>>>> rte_eth_tx_prepare function. Therefore, the TX prepare function of the
>>>>>> slave devices will never be invoked. When hardware offloading such as
>>>>>> CKSUM and TSO are enabled for some drivers, tx_prepare needs to be used
>>>>>> to adjust packets (for example, set correct pseudo packet headers).
>>>>>> Otherwise, related offloading fails and even packets are sent
>>>>>> incorrectly. Due to this limitation, the bonded device cannot use these
>>>>>> HW offloading in the Tx direction.
>>>>>>
>>>>>> Because packet sending algorithms are numerous and complex in bond PMD,
>>>>>> it is hard to design the callback for rte_eth_tx_prepare. In this patch,
>>>>>> the tx_prepare callback of bonding PMD is not implemented. Instead,
>>>>>> rte_eth_tx_prepare has been called in tx_burst callback. And a global
>>>>>> variable is introduced to control whether the bonded device need call
>>>>>> the rte_eth_tx_prepare. If upper-layer users need to use some TX
>>>>>> offloading that depend on tx_prepare , they should enable the preparation
>>>>>> function. In this way, the bonded device will call the rte_eth_tx_prepare
>>>>>> for the fast path packets in the tx_burst callback.
>>>
>>> I admit that I didn't look at the implementation yet, but it sounds like
>>> overcomplication to me. Can't we just have a new TX function for bonding PMD
>>> when TX offloads are enabled? And inside that function we will do:
>>> tx_prepare(); tx_burst(); for selected device.
>>
>> The solution you mentioned is workable and may perform better. However, the current
>> solution is also simple and has a limited impact on performance. It is actually:
>> if (tx_prepare_enable)
>> 	tx_prepare();
>> tx_burst();
>>
>> Overall, it adds almost only one judgment to the case where the related Tx offloads
>> is not turned on.
>>
>>> We can select this function at setup stage analysing requested by user TX offloads.
>>>
>>
>> In PMDs, it is a common practice to select different Tx/Rx function during the setup
>> phase. But for a 'vdev' device like Bonding, we may need to think more about it.
>> The reasons are explained below.
>>>
>>>>>>
>>>>>
>>>>> What do you think to add a devarg to bonding PMD to control the tx_prepare?
>>>>> It won't be as dynamic as API, since it can be possible to change the behavior after application is started with API, but do we really need
>>>> this?
>>>>
>>>> If an API is not added, unnecessary constraints may be introduced. If the
>>>> bonding device is created through the rte_eth_bond_create interface instead
>>>> devarg "vdev", this function cannot be used because devargs does not take effect
>>>> in this case. But from an ease-of-use perspective, adding a devarg is a good
>>>> idea. I will add related implementations in the later official patches.
>>>
>>> I am also against introducing new devarg to control tx_prepare() invocation.
>>> I think at dev_config/queue_setup phase PMD will have enough information to decide.
>>>
>> Currently, the community does not specify which Tx offloads need to invoke tx_prepare.
> 
> I think inside bond PMD we can safely assume that any TX offload does need tx_prepare().
> If that's not the case then slave dev tx_prepare pointer will be NULL and rte_eth_tx_prepare()
> will be just a NOOP. 

Get it. I agree that these decisions should be offloaded directly into PMDs.
In the formal patch, the API that used to control enable states will be deleted.
> 
>> For Vdev devices such as bond, all NIC devices need to be considered. Generally,
>> tx_prepare is used in CKSUM and TSO. It is possible that for some NIC devices, even
>> CKSUM and TSO do not need to invoke tx_prepare, or for some NIC devices, there are
>> other Tx offloads that need to call tx_prepare. From this perspective, leaving the
>> choice to the user seems to be a better choice.
> 
> Wonder how user will know when to enable/disable it?
> As you said it depends on the underlying HW/PMD and can change from system to system?

Generally, decisions need to be made based on debugging results, which is not good.
> I think it is PMD that needs to take this decision, and I think the safest bet might be to enable
> it when any TX offloads was enabled by user.
> 

I agree that these decisions should be made by the PMDs. Even, I think the tx_prepare()
should always be called in bonding, its impact on performance should be directly controlled
by the PMDs.
>>>>
>>>> If I understand correctly, the current community does not want to introduce
>>>> more private APIs for PMDs. However, the absence of an API on this issue would
>>>> introduce some unnecessary constraints, and from that point of view, I think
>>>> adding an API seems necessary.
>>>>>
>>>>>> Chengchang Tang (2):
>>>>>>    net/bonding: add Tx prepare for bonding
>>>>>>    app/testpmd: add cmd for bonding Tx prepare
>>>>>>
>>>>>>   app/test-pmd/cmdline.c                      | 66 +++++++++++++++++++++++++++++
>>>>>>   doc/guides/testpmd_app_ug/testpmd_funcs.rst |  9 ++++
>>>>>>   drivers/net/bonding/eth_bond_private.h      |  1 +
>>>>>>   drivers/net/bonding/rte_eth_bond.h          | 29 +++++++++++++
>>>>>>   drivers/net/bonding/rte_eth_bond_api.c      | 28 ++++++++++++
>>>>>>   drivers/net/bonding/rte_eth_bond_pmd.c      | 33 +++++++++++++--
>>>>>>   drivers/net/bonding/version.map             |  5 +++
>>>>>>   7 files changed, 167 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> --
>>>>>> 2.7.4
>>>>>>
>>>>>
>>>>>
>>>>> .
>>>>>
>>>
>