linux-kernel - Re: [PATCH net-next] page_pool: add a test module for page

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Message-ID: <17df1bfe-4e73-464e-8802-019eb13159e3@huawei.com>
Date: Wed, 11 Sep 2024 19:32:55 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Jesper Dangaard Brouer <hawk@...nel.org>, Mina Almasry
	<almasrymina@...gle.com>
CC: <ilias.apalodimas@...aro.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Shuah Khan <shuah@...nel.org>,
	<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH net-next] page_pool: add a test module for page_pool

On 2024/9/10 19:27, Jesper Dangaard Brouer wrote:
...

>>
>> The main issue I remembered was that it only support x86:(
>>
> 
> Yes, because I've added ASM code for reading TSC counter in a very
> precise manor. Given we run many iterations, then I don't think we
> need this precise reading.  I guess it can simply be replaced with
> get_cycles() or get_cycles64().  Then it should work on all archs.

Agreed.

> 
> The code already supports wall-clock time via ktime_get() (specifically
> ktime_get_real_ts64()).
> 
> 
>>>
>>> My preference here (for the performance part) is to upstream the
>>> out-of-tree tests that Jesper (and probably others) are using, rather
>>> than adding a new performance test that is not as battle-hardened.
>>
>> I looked through the out-of-tree tests again, it seems we can take the
>> best of them.
>> For Jesper' ko:
>> It seems we can do prefill as something that pp_fill_ptr_ring() does
>> in bench_page_pool_simple.c to avoid the noise from the page allocator.
>>
>>
>> For the ko in this patch:
>> It uses NAPI instead of tasklet mimicking the NAPI context, support
>> PP_FLAG_DMA_MAP flag testing, and return '-EAGAIN' in module_init()
>> to use perf stat for collecting and calculating performance data.
>>
> My bench don't return minus-number on module load, because I used perf
> record, and to see symbols decoded with perf report, I needed the module
> to be loaded.
> 
> I started on reading the PMU counters[1] around the bench loop, it works
> if enabling PMU counters yourself/manually, but I never finished that work.
> 
>  [1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/include/linux/time_bench.h#L195-L209
> 
> 
>> Is there other testcase or better practicing that we can learn from
>> Jesper' out of tree ko?
>>
> 
> I created a time_bench.c [2] module that other modules [3] can use to
> easier reuse the benchmarking code in other modules.
> 
>  [2] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/time_bench.c
> 
>  [3] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_simple.c

Will take a look at it, thanks.

> 
> --Jesper