Re: [PATCH v4] net/ice: improve performance of RX timestamp offload

[Kevin Traynor <ktraynor@redhat.com>]

On 24/03/2022 13:05, Zhang, Qi Z wrote:
> 
> 
>> -----Original Message-----
>> From: Kevin Traynor <ktraynor@redhat.com>
>> Sent: Thursday, March 24, 2022 8:18 PM
>> To: Zhang, Qi Z <qi.z.zhang@intel.com>; Wu, Wenjun1
>> <wenjun1.wu@intel.com>; dev@dpdk.org; Yang, Qiming
>> <qiming.yang@intel.com>
>> Cc: Van Haaren, Harry <harry.van.haaren@intel.com>; Su, Simei
>> <simei.su@intel.com>; Luca Boccassi <bluca@debian.org>; Christian Ehrhardt
>> <christian.ehrhardt@canonical.com>
>> Subject: Re: [PATCH v4] net/ice: improve performance of RX timestamp
>> offload
>>
>> On 24/03/2022 11:51, Zhang, Qi Z wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Kevin Traynor <ktraynor@redhat.com>
>>>> Sent: Thursday, March 24, 2022 7:17 PM
>>>> To: Zhang, Qi Z <qi.z.zhang@intel.com>; Wu, Wenjun1
>>>> <wenjun1.wu@intel.com>; dev@dpdk.org; Yang, Qiming
>>>> <qiming.yang@intel.com>
>>>> Cc: Van Haaren, Harry <harry.van.haaren@intel.com>; Su, Simei
>>>> <simei.su@intel.com>; Luca Boccassi <bluca@debian.org>; Christian
>>>> Ehrhardt <christian.ehrhardt@canonical.com>
>>>> Subject: Re: [PATCH v4] net/ice: improve performance of RX timestamp
>>>> offload
>>>>
>>>> On 24/03/2022 09:09, Zhang, Qi Z wrote:
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Wu, Wenjun1 <wenjun1.wu@intel.com>
>>>>>> Sent: Monday, February 28, 2022 3:36 PM
>>>>>> To: dev@dpdk.org; Zhang, Qi Z <qi.z.zhang@intel.com>; Yang, Qiming
>>>>>> <qiming.yang@intel.com>
>>>>>> Cc: Van Haaren, Harry <harry.van.haaren@intel.com>; Su, Simei
>>>>>> <simei.su@intel.com>; Wu, Wenjun1 <wenjun1.wu@intel.com>
>>>>>> Subject: [PATCH v4] net/ice: improve performance of RX timestamp
>>>>>> offload
>>>>>>
>>>>>> Previously, each time a burst of packets is received, SW reads HW
>>>>>> register and assembles it and the timestamp from descriptor
>>>>>> together to get the complete 64 bits timestamp.
>>>>>>
>>>>>> This patch optimizes the algorithm. The SW only needs to check the
>>>>>> monotonicity of the low 32bits timestamp to avoid crossing borders.
>>>>>> Each time before SW receives a burst of packets, it should check
>>>>>> the time difference between current time and last update time to
>>>>>> avoid the low 32 bits timestamp cycling twice.
>>>>>>
>>>>>> Signed-off-by: Wenjun Wu <wenjun1.wu@intel.com>
>>>>>
>>>>> Added cc stable
>>>>>
>>>>
>>>> Hi Qi. The DPDK documentation has guidance about what should be
>>>> backported to LTS [0] and distinguishes between fixes and performance
>>>> improvements. Please try and stick with this when applying patches or
>>>> let LTS maintainers know if there is a debatable case.
>>>
>>> Thanks for the comments
>>> Yes, actually this is about a 50% ~ 70% performance improvement, which
>>> maybe critical for some performance sensitive use cases.(e.g. network
>>> forensics) So I'd like to defend with below case
>>>
>>> An existing feature in LTS is not usable as intended without it.
>>>
>>
>> If that is the case, then I think the commitlog should be re-written. It just
>> talks about the code changes, there's nothing about an impact to an existing
>> use case that was unusuable and is now fixed.
> 
> OK, I updated with below commit log in dpdk-next-net-intel.
> Kevin , Wenjun, let me know if anything I missed.
> 
>      Previously, each time a burst of packets is received, SW reads HW
>      register and assembles it and the timestamp from descriptor together to
>      get the complete 64 bits timestamp.
> 
>      This patch optimizes the algorithm. The SW only needs to check the
>      monotonicity of the low 32bits timestamp to avoid crossing borders.
>      Each time before SW receives a burst of packets, it should check the
>      time difference between current time and last update time to avoid
>      the low 32 bits timestamp cycling twice.
> 
>      The patch proved a 50% ~ 70% single core performance improvement on a
>      main stream Xeon server, and it is necessary to be backport to LTS release,
>      as this fix the performance gap for some use cases.
> 

The comment about backport to LTS can be removed. That is an operational 
comment, so not really relevant to a future reader trying to understand 
the commit.

thanks,
Kevin.

> Thanks
> Qi
> 
>>
>>> Thanks
>>> Qi
>>>
>>>>
>>>> thanks,
>>>> Kevin.
>>>>
>>>> [0]
>>>> http://doc.dpdk.org/guides-21.11/contributing/stable.html#what-change
>>>> s-
>>>> should-be-backported
>>>
>>>>
>>>>> Acked-by: Qi Zhang <qi.z.zhang@intel.com>
>>>>>
>>>>> Applied to dpdk-next-net-intel.
>>>>>
>>>>> Thanks
>>>>> Qi
>>>>>
>>>>
>>>
>