linux-kernel - Re: [PATCH v3] sched/isolation: add a workqueue parameter onto isolcpus to constrain unbound CPUs

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Message-ID: <ZJoYNzXfQjgocqvj@lothringen>
Date:   Tue, 27 Jun 2023 00:59:03 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     tj@...nel.org, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, fuyuanli@...iglobal.com,
        zwp10758@...il.com, zyhtheonly@...il.com, zyhtheonly@...h.net
Subject: Re: [PATCH v3] sched/isolation: add a workqueue parameter onto
 isolcpus to constrain unbound CPUs

On Thu, Jun 22, 2023 at 11:22:17AM +0800, tiozhang wrote:
> Motivation of doing this is to better improve boot times for devices when
> we want to prevent our workqueue works from running on some specific CPUs,
> i,e, some CPUs are busy with interrupts.
> 
> Also remove HK_FLAG_WQ from nohz_full to prevent nohz_full overriding
> workqueue's cpu config.

But then nohz_full= doesn't re-affine workqueues anymore, right?

> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: tiozhang <tiozhang@...iglobal.com>
> ---
>  kernel/sched/isolation.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 373d42c707bc..5cd67c51622e 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -181,8 +181,8 @@ 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;
> +	flags = HK_FLAG_TICK | HK_FLAG_TIMER | HK_FLAG_RCU | HK_FLAG_MISC
> +		| HK_FLAG_KTHREAD;
>  
>  	return housekeeping_setup(str, flags);
>  }
> @@ -208,6 +208,12 @@ static int __init housekeeping_isolcpus_setup(char *str)
>  			continue;
>  		}
>  
> +		if (!strncmp(str, "workqueue,", 10)) {
> +			str += 10;
> +			flags |= HK_FLAG_WQ;
> +			continue;
> +		}
> +

I'm planning on removing HK_FLAG_TICK, HK_FLAG_WQ, HK_FLAG_TIMER, HK_FLAG_RCU,
HK_FLAG_MISC and HK_FLAG_KTHREAD and merge them all together. Also the problem with
these flags is that once they are modified on boot, you can't modify them later.

I much prefer what was done in this patch:

  https://lore.kernel.org/all/20230623073033.GA6584@didi-ThinkCentre-M930t-N000/

Thanks!

>  		if (!strncmp(str, "managed_irq,", 12)) {
>  			str += 12;
>  			flags |= HK_FLAG_MANAGED_IRQ;
> -- 
> 2.17.1
>