linux-kernel - Re: [PATCH sched_ext/for-6.18] sched_ext: Add migration-disabled counter to error state dump

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Message-ID: <aMwsj3SOkCdMNk3F@gpd4>
Date: Thu, 18 Sep 2025 18:00:15 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	sched-ext@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH sched_ext/for-6.18] sched_ext: Add migration-disabled
 counter to error state dump

On Thu, Sep 18, 2025 at 05:49:20AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Thu, Sep 18, 2025 at 11:29:28AM +0200, Andrea Righi wrote:
> > Include the task's migration-disabled counter when dumping task state
> > during an error exit.
> > 
> > This can help diagnose cases where tasks can get stuck, because they're
> > unable to migrate elsewhere.
> > 
> > Signed-off-by: Andrea Righi <arighi@...dia.com>
> > ---
> >  kernel/sched/ext.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> > index 477eccf023388..e03bb51364661 100644
> > --- a/kernel/sched/ext.c
> > +++ b/kernel/sched/ext.c
> > @@ -4167,7 +4167,8 @@ static void scx_dump_task(struct seq_buf *s, struct scx_dump_ctx *dctx,
> >  		  p->scx.sticky_cpu, p->scx.holding_cpu, dsq_id_buf);
> >  	dump_line(s, "      dsq_vtime=%llu slice=%llu weight=%u",
> >  		  p->scx.dsq_vtime, p->scx.slice, p->scx.weight);
> > -	dump_line(s, "      cpus=%*pb", cpumask_pr_args(p->cpus_ptr));
> > +	dump_line(s, "      cpus=%*pb migration_disabled=%u", cpumask_pr_args(p->cpus_ptr),
> 
> Can you abbreviate this a bit? We have limited dump buffer size and real
> estate. Wouldn't e.g. no_mig= achieve the same with a lot less space?

Oh yes, good point. I think no_mig= is clear enough, or even nomig=. And if
it isn't clear, people can always check the code to see what it refers to.

Will send a v2 with this change.

Thanks,
-Andrea