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

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Message-ID: <fc61be3b-816a-44d9-aa56-d5338ccd3342@linux.dev>
Date: Wed, 24 Jul 2024 10:31:55 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Chuyi Zhou <zhouchuyi@...edance.com>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com
Cc: linux-kernel@...r.kernel.org, joshdon@...gle.com
Subject: Re: [PATCH v2 2/2] sched/core: Avoid unnecessary update in
 tg_set_cfs_bandwidth

On 2024/7/23 20:20, Chuyi Zhou wrote:
> 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>
> ---
>   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;
> +

Should break this to multiple lines? Feel free to add:

Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>

>   	ret = __cfs_schedulable(tg, period, quota);
>   	if (ret)
>   		return ret;