linux-kernel - Re: [PATCH] Revert "isolcpus: Affine unbound kernel threads to housekeeping cpus"

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Message-ID: <20210507201600.GA66223@lothringen>
Date:   Fri, 7 May 2021 22:16:00 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] Revert "isolcpus: Affine unbound kernel threads to
 housekeeping cpus"

On Fri, May 07, 2021 at 01:57:10PM -0300, Marcelo Tosatti wrote:
> 
> 
> commit 9cc5b8656892a72438ee7deb introduced a new housekeeping flag,
> HK_FLAG_KTHREAD, that when enabled sets the CPU affinity for the 
> kthreadd process (therefore all unbounded kernel threads created
> from that point on will use the housekeeping cpumask).
> 
> This is not necessary, since its possible to control placement of
> kthreadd from userspace:
> 
> # taskset -c -p 0 `pgrep kthreadd`
> pid 2's current affinity list: 1
> pid 2's new affinity list: 0
> 
> Unbounded kernel threads started from that point on will inherit
> the kthreadd cpumask.

Hmm, but look below:

> @@ -405,8 +404,7 @@ struct task_struct *__kthread_create_on_
>  		 * The kernel thread should not inherit these properties.
>  		 */
>  		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
> -		set_cpus_allowed_ptr(task,
> -				     housekeeping_cpumask(HK_FLAG_KTHREAD));
> +		set_cpus_allowed_ptr(task, cpu_possible_mask);

That inheritance is then overriden, right?

Thanks.