linux-kernel - Re: [PATCH v3 3/5] sched/fair: Switch to task based throttle model

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Message-ID: <xhsmhh5y9j3ut.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Thu, 14 Aug 2025 17:54:34 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: Aaron Lu <ziqianlu@...edance.com>
Cc: Ben Segall <bsegall@...gle.com>, K Prateek Nayak
 <kprateek.nayak@....com>, Peter Zijlstra <peterz@...radead.org>, Chengming
 Zhou <chengming.zhou@...ux.dev>, Josh Don <joshdon@...gle.com>, Ingo
 Molnar <mingo@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
 Xi Wang <xii@...gle.com>, linux-kernel@...r.kernel.org, Juri Lelli
 <juri.lelli@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>, Chuyi
 Zhou <zhouchuyi@...edance.com>, Jan Kiszka <jan.kiszka@...mens.com>,
 Florian Bezdeka <florian.bezdeka@...mens.com>, Songtang Liu
 <liusongtang@...edance.com>
Subject: Re: [PATCH v3 3/5] sched/fair: Switch to task based throttle model

On 12/08/25 16:48, Aaron Lu wrote:
> On Fri, Aug 08, 2025 at 01:45:11PM +0200, Valentin Schneider wrote:
>> On 08/08/25 18:13, Aaron Lu wrote:
>> > Let me run some scheduler benchmark to see how it impacts performance.
>> >
>> > I'm thinking maybe running something like hackbench on server platforms,
>> > first with quota not set and see if performance changes; then also test
>> > with quota set and see how performance changes.
>> >
>> > Does this sound good to you? Or do you have any specific benchmark and
>> > test methodology in mind?
>> >
>>
>> Yeah hackbench is pretty good for stressing the EQ/DQ paths.
>>
>
> Tested hackbench/pipe and netperf/UDP_RR on Intel EMR(2 sockets/240
> cpus) and AMD Genoa(2 sockets/384 cpus), the tldr is: there is no clear
> performance change between base and this patchset(head). Below is
> detailed test data:
> (turbo/boost disabled, cpuidle disabled, cpufreq set to performance)
>
> hackbench/pipe/loops=150000
> (seconds, smaller is better)
>
> On Intel EMR:
>
> nr_group          base             head          change
>  1              3.62±2.99%      3.61±10.42%      +0.28%
>  8              8.06±1.58%      7.88±5.82%       +2.23%
> 16             11.40±2.57%     11.25±3.72%       +1.32%
>
> For nr_group=16 case, configure a cgroup and set quota to half cpu and
> then let hackbench run in this cgroup:
>
>                  base             head           change
> quota=50%      18.35±2.40%     18.78±1.97%       -2.34%
>
> On AMD Genoa:
>
> nr_group          base             head          change
>  1             17.05±1.92%     16.99±2.81%       +0.35%
>  8             16.54±0.71%     16.73±1.18%       -1.15%
> 16             27.04±0.39%     26.72±2.37%       +1.18%
>
> For nr_group=16 case, configure a cgroup and set quota to half cpu and
> then let hackbench run in this cgroup:
>
>                   base             head          change
> quota=50%      43.79±1.10%     44.65±0.37%       -1.96%
>
> Netperf/UDP_RR/testlen=30s
> (throughput, higher is better)
>
> 25% means nr_clients set to 1/4 nr_cpu, 50% means nr_clients is 1/2
> nr_cpu, etc.
>
> On Intel EMR:
>
> nr_clients     base                 head             change
>   25%       83,567±0.06%         84,298±0.23%        +0.87%
>   50%       61,336±1.49%         60,816±0.63%        -0.85%
>   75%       40,592±0.97%         40,461±0.14%        -0.32%
>  100%       31,277±2.11%         30,948±1.84%        -1.05%
>
> For nr_clients=100% case, configure a cgroup and set quota to half cpu
> and then let netperf run in this cgroup:
>
> nr_clients     base                 head             change
>  100%       25,532±0.56%         26,772±3.05%        +4.86%
>
> On AMD Genoa:
>
> nr_clients     base                 head             change
>  25%        12,443±0.40%         12,525±0.06%        +0.66%
>  50%        11,403±0.35%         11,472±0.50%        +0.61%
>  75%        10,070±0.19%         10,071±0.95%         0.00%
> 100%         9,947±0.80%          9,881±0.58%        -0.66%
>
> For nr_clients=100% case, configure a cgroup and set quota to half cpu
> and then let netperf run in this cgroup:
>
> nr_clients     base                 head             change
> 100%         4,954±0.24%          4,952±0.14%         0.00%

Thank you for running these, looks like mostly slightly bigger variance on
a few of these but that's about it.

I would also suggest running similar benchmarks but with deeper
hierarchies, to get an idea of how much worse unthrottle_cfs_rq() can get
when tg_unthrottle_up() goes up a bigger tree.