linux-kernel - Re: [PATCH 1/3] sched/isolation: Add HK_FLAG_SCHED to nohz

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Message-ID: <ZtcK3aF_d3BUhiVz@localhost.localdomain>
Date: Tue, 3 Sep 2024 15:10:53 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] sched/isolation: Add HK_FLAG_SCHED to nohz_full

Le Sun, Aug 18, 2024 at 07:45:18PM -0400, Waiman Long a écrit :
> The HK_FLAG_SCHED/HK_TYPE_SCHED flag is defined and is also used
> in kernel/sched/fair.c since commit de201559df87 ("sched/isolation:
> Introduce housekeeping flags"). However, the corresponding cpumask isn't
> currently updated anywhere. So the mask is always cpu_possible_mask.
> 
> Add it in nohz_full setup so that nohz_full CPUs will now be removed
> from HK_TYPE_SCHED cpumask.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  kernel/sched/isolation.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 5891e715f00d..a514994af319 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -196,7 +196,7 @@ static int __init housekeeping_nohz_full_setup(char *str)
>  	unsigned long flags;
>  
>  	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
> -		HK_FLAG_MISC | HK_FLAG_KTHREAD;
> +		HK_FLAG_MISC | HK_FLAG_KTHREAD | HK_FLAG_SCHED;
>  
>  	return housekeeping_setup(str, flags);
>  }

find_new_ilb() already has HK_FLAG_MISC to prevent an isolated CPU
from being elected as an ilb. So I think we should simply remove HK_FLAG_SCHED.

Thanks.