linux-kernel - Re: [PATCH] sched/fair: Correct CPU selection from isolated domain

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Message-ID: <2c7d8983-2004-4886-32b2-93091a0c0679@huawei.com>
Date: Tue, 30 Jul 2024 17:02:28 +0800
From: zhengzucheng <zhengzucheng@...wei.com>
To: wujing <realwujing@...com>, <mingo@...hat.com>, <peterz@...radead.org>
CC: <linux-kernel@...r.kernel.org>, <dongml2@...natelecom.cn>, QiLiang Yuan
	<yuanql9@...natelecom.cn>
Subject: Re: [PATCH] sched/fair: Correct CPU selection from isolated domain

it has already been addressed by the following patches in tip/sched/core:

8aeaffef8c6e ("sched/fair: Take the scheduling domain into account in 
select_idle_smt()")
23d04d8c6b8e ("sched/fair: Take the scheduling domain into account in 
select_idle_core()")

在 2024/7/30 15:10, wujing 写道:
> We encountered an issue where the kernel thread `ksmd` runs on the PMD
> dedicated isolated core, leading to high latency in OVS packets.
>
> Upon analysis, we discovered that this is caused by the current
> select_idle_smt() function not taking the sched_domain mask into account.
>
> Kernel version: linux-4.19.y
>
> Signed-off-by: wujing <realwujing@...com>
> Signed-off-by: QiLiang Yuan <yuanql9@...natelecom.cn>
> ---
>   kernel/sched/fair.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 09f82c84474b..0950cabfc1d0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6171,7 +6171,8 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t
>   		return -1;
>   
>   	for_each_cpu(cpu, cpu_smt_mask(target)) {
> -		if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
> +		if (!cpumask_test_cpu(cpu, &p->cpus_allowed) ||
> +			!cpumask_test_cpu(cpu, sched_domain_span(sd)))
>   			continue;
>   		if (available_idle_cpu(cpu))
>   			return cpu;