Re: [PATCH net-next v25 00/13] Device Memory TCP

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On 2024/9/10 0:54, Mina Almasry wrote:
> On Mon, Sep 9, 2024 at 4:21 AM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:
>>
>> On 2024/9/9 13:43, Mina Almasry wrote:
>>
>>>
>>> Perf - page-pool benchmark:
>>> ---------------------------
>>>
>>> bench_page_pool_simple.ko tests with and without these changes:
>>> https://pastebin.com/raw/ncHDwAbn
>>>
>>> AFAIK the number that really matters in the perf tests is the
>>> 'tasklet_page_pool01_fast_path Per elem'. This one measures at about 8
>>> cycles without the changes but there is some 1 cycle noise in some
>>> results.
>>>
>>> With the patches this regresses to 9 cycles with the changes but there
>>> is 1 cycle noise occasionally running this test repeatedly.
>>>
>>> Lastly I tried disable the static_branch_unlikely() in
>>> netmem_is_net_iov() check. To my surprise disabling the
>>> static_branch_unlikely() check reduces the fast path back to 8 cycles,
>>> but the 1 cycle noise remains.
>>
>> Sorry for the late report, as I was adding a testing page_pool ko basing
>> on [1] to avoid introducing performance regression when fixing the bug in
>> [2].
>> I used it to test the performance impact of devmem patchset for page_pool
>> too, it seems there might be some noticable performance impact quite stably
>> for the below testcases, about 5%~16% performance degradation as below in
>> the arm64 system:
>>
> 
> Correct me if I'm wrong here, but on the surface here it seems that
> you're re-reporting a known issue. Consensus seems to be that it's a
> non-issue.
> 
> In v6 I reported that the bench_page_pool_simple.ko test reports a 1
> cycle regression with these patches, from 8->9 cycles. That is roughly
> consistent with the 5-15% you're reporting.


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