linux-kernel - Re: [PATCH net-next v6 0/8] fix two bugs related to page

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Message-ID: <7d26402a-bcd1-4e5f-bbf1-8b0a433ee8cd@huawei.com>
Date: Wed, 8 Jan 2025 17:36:50 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Jesper Dangaard Brouer <hawk@...nel.org>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>
CC: <liuyonglong@...wei.com>, <fanghaiqing@...wei.com>,
	<zhangkun09@...wei.com>, Alexander Lobakin <aleksander.lobakin@...el.com>,
	Robin Murphy <robin.murphy@....com>, Alexander Duyck
	<alexander.duyck@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, IOMMU
	<iommu@...ts.linux.dev>, MM <linux-mm@...ck.org>, Alexei Starovoitov
	<ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend
	<john.fastabend@...il.com>, Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	<netdev@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>,
	<bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH net-next v6 0/8] fix two bugs related to page_pool

On 2025/1/7 22:26, Jesper Dangaard Brouer wrote:
> 
> 
> On 06/01/2025 14.01, 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.
>>
>> Before this patchset:
>> root@(none)$ insmod bench_page_pool_simple.ko
>> [  323.367627] bench_page_pool_simple: Loaded
>> [  323.448747] time_bench: Type:for_loop Per elem: 0 cycles(tsc) 0.769 ns (step:0) - (measurement period time:0.076997150 sec time_interval:76997150) - (invoke count:100000000 tsc_interval:7699707)
>> [  324.812884] time_bench: Type:atomic_inc Per elem: 1 cycles(tsc) 13.468 ns (step:0) - (measurement period time:1.346855130 sec time_interval:1346855130) - (invoke count:100000000 tsc_interval:134685507)
>> [  324.980875] time_bench: Type:lock Per elem: 1 cycles(tsc) 15.010 ns (step:0) - (measurement period time:0.150101270 sec time_interval:150101270) - (invoke count:10000000 tsc_interval:15010120)
>> [  325.652195] time_bench: Type:rcu Per elem: 0 cycles(tsc) 6.542 ns (step:0) - (measurement period time:0.654213000 sec time_interval:654213000) - (invoke count:100000000 tsc_interval:65421294)
>> [  325.669215] bench_page_pool_simple: time_bench_page_pool01_fast_path(): Cannot use page_pool fast-path
>> [  325.974848] time_bench: Type:no-softirq-page_pool01 Per elem: 2 cycles(tsc) 29.633 ns (step:0) - (measurement period time:0.296338200 sec time_interval:296338200) - (invoke count:10000000 tsc_interval:29633814)
> 
> (referring to above line, below)
> 
>> [  325.993517] bench_page_pool_simple: time_bench_page_pool02_ptr_ring(): Cannot use page_pool fast-path
>> [  326.576636] time_bench: Type:no-softirq-page_pool02 Per elem: 5 cycles(tsc) 57.391 ns (step:0) - (measurement period time:0.573911820 sec time_interval:573911820) - (invoke count:10000000 tsc_interval:57391174)
>> [  326.595307] bench_page_pool_simple: time_bench_page_pool03_slow(): Cannot use page_pool fast-path
>> [  328.422661] time_bench: Type:no-softirq-page_pool03 Per elem: 18 cycles(tsc) 181.849 ns (step:0) - (measurement period time:1.818495880 sec time_interval:1818495880) - (invoke count:10000000 tsc_interval:181849581)
>> [  328.441681] bench_page_pool_simple: pp_tasklet_handler(): in_serving_softirq fast-path
>> [  328.449584] bench_page_pool_simple: time_bench_page_pool01_fast_path(): in_serving_softirq fast-path
>> [  328.755031] time_bench: Type:tasklet_page_pool01_fast_path Per elem: 2 cycles(tsc) 29.632 ns (step:0) - (measurement period time:0.296327910 sec time_interval:296327910) - (invoke count:10000000 tsc_interval:29632785)
> 
> It is strange that fast-path "tasklet_page_pool01_fast_path" isn't
> faster than above "no-softirq-page_pool01".
> They are both 29.633 ns.
> 
> What hardware is this?

Arm64 server, as the testing module doesn't support arm64, so get_cycles()
in [1] is used to do time keeping instead of using x86 asm instruction.

1. https://lore.kernel.org/lkml/caf31b5e-0e8f-4844-b7ba-ef59ed13b74e@arm.com/T/

> 
> e.g. the cycle count of 2 cycles(tsc) seem strange.
> 
> On my testlab hardware Intel CPU E5-1650 v4 @3.60GHz
> My fast-path numbers say 5.202 ns (18 cycles) for "tasklet_page_pool01_fast_path"
> 
> 
> Raw data look like this
> 
> [Tue Jan  7 15:15:18 2025] bench_page_pool_simple: pp_tasklet_handler(): in_serving_softirq fast-path
> [Tue Jan  7 15:15:18 2025] bench_page_pool_simple: time_bench_page_pool01_fast_path(): in_serving_softirq fast-path
> [Tue Jan  7 15:15:18 2025] time_bench: Type:tasklet_page_pool01_fast_path Per elem: 18 cycles(tsc) 5.202 ns (step:0) - (measurement period time:0.052020430 sec time_interval:52020430) - (invoke count:10000000 tsc_interval:187272981)
> [Tue Jan  7 15:15:18 2025] bench_page_pool_simple: time_bench_page_pool02_ptr_ring(): in_serving_softirq fast-path
> [Tue Jan  7 15:15:19 2025] time_bench: Type:tasklet_page_pool02_ptr_ring Per elem: 55 cycles(tsc) 15.343 ns (step:0) - (measurement period time:0.153438301 sec time_interval:153438301) - (invoke count:10000000 tsc_interval:552378168)
> [Tue Jan  7 15:15:19 2025] bench_page_pool_simple: time_bench_page_pool03_slow(): in_serving_softirq fast-path
> [Tue Jan  7 15:15:19 2025] time_bench: Type:tasklet_page_pool03_slow Per elem: 243 cycles(tsc) 67.725 ns (step:0) - (measurement period time:0.677255574 sec time_interval:677255574) - (invoke count:10000000 tsc_interval:2438124315)
> 
> 
>> [  328.774308] bench_page_pool_simple: time_bench_page_pool02_ptr_ring(): in_serving_softirq fast-path
>> [  329.578579] time_bench: Type:tasklet_page_pool02_ptr_ring Per elem: 7 cycles(tsc) 79.523 ns (step:0) - (measurement period time:0.795236560 sec time_interval:795236560) - (invoke count:10000000 tsc_interval:79523650)
>> [  329.597769] bench_page_pool_simple: time_bench_page_pool03_slow(): in_serving_softirq fast-path
>> [  331.507501] time_bench: Type:tasklet_page_pool03_slow Per elem: 19 cycles(tsc) 190.104 ns (step:0) - (measurement period time:1.901047510 sec time_interval:1901047510) - (invoke count:10000000 tsc_interval:190104743)
>>
>> After this patchset:
>> root@(none)$ insmod bench_page_pool_simple.ko
>> [  138.634758] bench_page_pool_simple: Loaded
>> [  138.715879] time_bench: Type:for_loop Per elem: 0 cycles(tsc) 0.769 ns (step:0) - (measurement period time:0.076972720 sec time_interval:76972720) - (invoke count:100000000 tsc_interval:7697265)
>> [  140.079897] time_bench: Type:atomic_inc Per elem: 1 cycles(tsc) 13.467 ns (step:0) - (measurement period time:1.346735370 sec time_interval:1346735370) - (invoke count:100000000 tsc_interval:134673531)
>> [  140.247841] time_bench: Type:lock Per elem: 1 cycles(tsc) 15.005 ns (step:0) - (measurement period time:0.150055080 sec time_interval:150055080) - (invoke count:10000000 tsc_interval:15005497)
>> [  140.919072] time_bench: Type:rcu Per elem: 0 cycles(tsc) 6.541 ns (step:0) - (measurement period time:0.654125000 sec time_interval:654125000) - (invoke count:100000000 tsc_interval:65412493)
>> [  140.936091] bench_page_pool_simple: time_bench_page_pool01_fast_path(): Cannot use page_pool fast-path
>> [  141.246985] time_bench: Type:no-softirq-page_pool01 Per elem: 3 cycles(tsc) 30.159 ns (step:0) - (measurement period time:0.301598160 sec time_interval:301598160) - (invoke count:10000000 tsc_interval:30159812)
>> [  141.265654] bench_page_pool_simple: time_bench_page_pool02_ptr_ring(): Cannot use page_pool fast-path
>> [  141.976265] time_bench: Type:no-softirq-page_pool02 Per elem: 7 cycles(tsc) 70.140 ns (step:0) - (measurement period time:0.701405780 sec time_interval:701405780) - (invoke count:10000000 tsc_interval:70140573)
>> [  141.994933] bench_page_pool_simple: time_bench_page_pool03_slow(): Cannot use page_pool fast-path
>> [  144.018945] time_bench: Type:no-softirq-page_pool03 Per elem: 20 cycles(tsc) 201.514 ns (step:0) - (measurement period time:2.015141210 sec time_interval:2015141210) - (invoke count:10000000 tsc_interval:201514113)
>> [  144.037966] bench_page_pool_simple: pp_tasklet_handler(): in_serving_softirq fast-path
>> [  144.045870] bench_page_pool_simple: time_bench_page_pool01_fast_path(): in_serving_softirq fast-path
>> [  144.205045] time_bench: Type:tasklet_page_pool01_fast_path Per elem: 1 cycles(tsc) 15.005 ns (step:0) - (measurement period time:0.150056510 sec time_interval:150056510) - (invoke count:10000000 tsc_interval:15005645)
> 
> This 15.005 ns looks like a significant improvement over 29.633 ns

It seems to be some performance variations here. There seems to be some
performance variations between doing test using 'taskset -c 0' and with
using 'taskset -c 1' too, I didn't get into the detail reason of performance
variations yet, as the performance variations seems to exist before this
patchset too.

> 
>> [  144.224320] bench_page_pool_simple: time_bench_page_pool02_ptr_ring(): in_serving_softirq fast-path
>> [  144.916044] time_bench: Type:tasklet_page_pool02_ptr_ring Per elem: 6 cycles(tsc) 68.269 ns (step:0) - (measurement period time:0.682693070 sec time_interval:682693070) - (invoke count:10000000 tsc_interval:68269300)
>> [  144.935234] bench_page_pool_simple: time_bench_page_pool03_slow(): in_serving_softirq fast-path
>> [  146.997684] time_bench: Type:tasklet_page_pool03_slow Per elem: 20 cycles(tsc) 205.376 ns (step:0) - (measurement period time:2.053766310 sec time_interval:2053766310) - (invoke count:10000000 tsc_interval:205376624)
>>
> 
> 
> Looks like I should also try out this patchset on my testlab, as this
> hardware seems significantly different than mine...

Yes, it would be much appreciated if it is also tested in your testlab.