linux-kernel - Re: [PATCH v2 2/2] sched/core: Avoid unnecessary update in tg_set_cfs

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Message-ID: <xm26h6cfzij5.fsf@google.com>
Date: Tue, 23 Jul 2024 18:27:10 -0700
From: Benjamin Segall <bsegall@...gle.com>
To: Chuyi Zhou <zhouchuyi@...edance.com>
Cc: mingo@...hat.com,  peterz@...radead.org,  juri.lelli@...hat.com,
  vincent.guittot@...aro.org,  dietmar.eggemann@....com,
  rostedt@...dmis.org,  mgorman@...e.de,  vschneid@...hat.com,
  chengming.zhou@...ux.dev,  linux-kernel@...r.kernel.org,
  joshdon@...gle.com
Subject: Re: [PATCH v2 2/2] sched/core: Avoid unnecessary update in
 tg_set_cfs_bandwidth

Chuyi Zhou <zhouchuyi@...edance.com> writes:

> In the kubernetes production environment, we have observed a high
> frequency of writes to cpu.max, approximately every 2~4 seconds for each
> cgroup, with the same value being written each time. This can result in
> unnecessary overhead, especially on machines with a large number of CPUs
> and cgroups.
>
> This is because kubelet and runc attempt to persist resource
> configurations through frequent updates with same value in this manner.
> While optimizations can be made to kubelet and runc to avoid such
> overhead(e.g. check the current value of cpu request/limit before writing
> to cpu.max), it is still worth to bail out from tg_set_cfs_bandwidth() if
> we attempt to update with the same value.
>
> Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>

Reviewed-by: Ben Segall <bsegall@...gle.com>

> ---
>  kernel/sched/core.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7720d34bd71b..0cc564f45511 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9090,6 +9090,9 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
>  	guard(cpus_read_lock)();
>  	guard(mutex)(&cfs_constraints_mutex);
>  
> +	if (cfs_b->period == ns_to_ktime(period) && cfs_b->quota == quota && cfs_b->burst == burst)
> +		return 0;
> +
>  	ret = __cfs_schedulable(tg, period, quota);
>  	if (ret)
>  		return ret;