linux-kernel - Re: [PATCH] sched/fair: Dequeue sched_delayed tasks when waking to a busy CPU

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Message-ID: <20241114112854.GA471026@pauld.westford.csb>
Date: Thu, 14 Nov 2024 06:28:54 -0500
From: Phil Auld <pauld@...hat.com>
To: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
	kprateek.nayak@....com, wuyun.abel@...edance.com,
	youssefesmat@...omium.org, tglx@...utronix.de
Subject: Re: [PATCH] sched/fair: Dequeue sched_delayed tasks when waking to a
 busy CPU

On Thu, Nov 14, 2024 at 12:07:03PM +0100 Mike Galbraith wrote:
> On Tue, 2024-11-12 at 17:15 +0100, Mike Galbraith wrote:
> > On Tue, 2024-11-12 at 10:41 -0500, Phil Auld wrote:
> > > On Tue, Nov 12, 2024 at 03:23:38PM +0100 Mike Galbraith wrote:
> > >
> > > >
> > > > We don't however have to let sched_delayed block SIS though.  Rendering
> > > > them transparent in idle_cpu() did NOT wreck the progression, so
> > > > maaaybe could help your regression.
> > > >
> > >
> > > You mean something like:
> > >
> > > if (rq->nr_running > rq->h_nr_delayed)
> > >        return 0;
> > >
> > > in idle_cpu() instead of the straight rq->nr_running check?
> >
> > Yeah, close enough.
> 
> The below is all you need.
> 
> Watching blockage rate during part of a netperf scaling run without, a
> bit over 2/sec was the highest it got, but with, that drops to the same
> zero as turning off the feature, so... relevance highly unlikely but
> not quite impossible?
>

I'll give this a try on my issue. This'll be simpler than the other way.

Thanks!



Cheers,
Phil


> ---
>  kernel/sched/fair.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9454,11 +9454,15 @@ int can_migrate_task(struct task_struct
> 
>  	/*
>  	 * We do not migrate tasks that are:
> +	 * 0) not runnable (not useful here/now, but are annoying), or
>  	 * 1) throttled_lb_pair, or
>  	 * 2) cannot be migrated to this CPU due to cpus_ptr, or
>  	 * 3) running (obviously), or
>  	 * 4) are cache-hot on their current CPU.
>  	 */
> +	if (p->se.sched_delayed)
> +		return 0;
> +
>  	if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
>  		return 0;
> 
> 

--