Re: [PATCH net-next v7 0/8] fix two bugs related to page_pool

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 15/01/2025 12.33, Yunsheng Lin wrote:
> On 2025/1/14 22:31, Jesper Dangaard Brouer wrote:
>>
>>
>> On 10/01/2025 14.06, Yunsheng Lin wrote:
>>> This patchset fix a possible time window problem for page_pool and
>>> the dma API misuse problem as mentioned in [1], and try to avoid the
>>> overhead of the fixing using some optimization.
>>>
>>>   From the below performance data, the overhead is not so obvious
>>> due to performance variations for time_bench_page_pool01_fast_path()
>>> and time_bench_page_pool02_ptr_ring, and there is about 20ns overhead
>>> for time_bench_page_pool03_slow() for fixing the bug.
>>>
>>
>> My benchmarking on x86_64 CPUs looks significantly different.
>>   - CPU: Intel(R) Xeon(R) CPU E5-1650 v4 @ 3.60GHz
>>
>> Benchmark (bench_page_pool_simple) results from before and after patchset:
>>
>> | Test name  | Cycles |       |    |Nanosec |        |       |      % |
>> | (tasklet_*)| Before | After |diff| Before |  After |  diff | change |
>> |------------+--------+-------+----+--------+--------+-------+--------|
>> | fast_path  |     19 |    24 |   5|  5.399 |  6.928 | 1.529 |   28.3 |
>> | ptr_ring   |     54 |    79 |  25| 15.090 | 21.976 | 6.886 |   45.6 |
>> | slow       |    238 |   299 |  61| 66.134 | 83.298 |17.164 |   26.0 |
>> #+TBLFM: $4=$3-$2::$7=$6-$5::$8=(($7/$5)*100);%.1f
>>
>> My above testing show a clear performance regressions across three
>> different page_pool operating modes.
> 
> I retested it on arm64 server patch by patch as the raw performance
> data in the attachment, it seems the result seemed similar as before.
> 
> Before this patchset:
>              fast_path              ptr_ring            slow
> 1.         31.171 ns               60.980 ns          164.917 ns
> 2.         28.824 ns               60.891 ns          170.241 ns
> 3.         14.236 ns               60.583 ns          164.355 ns
> 
> With patch 1-4:
> 4.         31.443 ns               53.242 ns          210.148 ns
> 5.         31.406 ns               53.270 ns          210.189 ns
> 
> With patch 1-5:
> 6.         26.163 ns               53.781 ns          189.450 ns
> 7.         26.189 ns               53.798 ns          189.466 ns
> 
> With patch 1-8:
> 8.         28.108 ns               68.199 ns          202.516 ns
> 9.         16.128 ns               55.904 ns          202.711 ns
> 
> I am not able to get hold of a x86 server yet, I might be able
> to get one during weekend.
> 
> Theoretically, patch 1-4 or 1-5 should not have much performance
> impact for fast_path and ptr_ring except for the rcu_lock mentioned
> in page_pool_napi_local(), so it would be good if patch 1-5 is also
> tested in your testlab with the rcu_lock removing in
> page_pool_napi_local().
> 

What are you saying?
  - (1) test patch 1-5
  - or (2) test patch 1-5 but revert patch 2 with page_pool_napi_local()

--Jesper

>>
>>
>> Data also available in:
>>   - https://github.com/xdp-project/xdp-project/blob/main/areas/mem/page_pool07_bench_DMA_fix.org
>>