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From: John Stultz <jstultz@google.com>
Date: Thu, 4 Jan 2024 16:01:56 -0800
Message-ID: <CANDhNCovyXRswmHA0dwNve32HUxiAQmExR+ALadzDQaATVj0nA@mail.gmail.com>
Subject: Re: [PATCH v7 20/23] sched: Push execution and scheduler context
 split into deadline and rt paths
To: Metin Kaya <metin.kaya@arm.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Joel Fernandes <joelaf@google.com>, 
	Qais Yousef <qyousef@google.com>, Ingo Molnar <mingo@redhat.com>, 
	Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>, 
	Vincent Guittot <vincent.guittot@linaro.org>, Dietmar Eggemann <dietmar.eggemann@arm.com>, 
	Valentin Schneider <vschneid@redhat.com>, Steven Rostedt <rostedt@goodmis.org>, 
	Ben Segall <bsegall@google.com>, Zimuzo Ezeozue <zezeozue@google.com>, 
	Youssef Esmat <youssefesmat@google.com>, Mel Gorman <mgorman@suse.de>, 
	Daniel Bristot de Oliveira <bristot@redhat.com>, Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>, 
	Boqun Feng <boqun.feng@gmail.com>, "Paul E. McKenney" <paulmck@kernel.org>, 
	Xuewen Yan <xuewen.yan94@gmail.com>, K Prateek Nayak <kprateek.nayak@amd.com>, 
	Thomas Gleixner <tglx@linutronix.de>, kernel-team@android.com
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On Fri, Dec 22, 2023 at 3:33=E2=80=AFAM Metin Kaya <metin.kaya@arm.com> wro=
te:
>
> On 20/12/2023 12:18 am, John Stultz wrote:
> > From: Connor O'Brien <connoro@google.com>
> >
> > In preparation for chain migration, push the awareness
> > of the split between execution and scheduler context
> > down into some of the rt/deadline code paths that deal
> > with load balancing.
> >
> > This patch was broken out from a larger chain migration
> > patch originally by Connor O'Brien.
> >
>
> Nit: Commit header is too long. ` paths` can be dropped.

Done.

> > @@ -2079,25 +2079,25 @@ static struct task_struct *pick_earliest_pushab=
le_dl_task(struct rq *rq, int cpu
> >
> >   static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
> >
> > -static int find_later_rq(struct task_struct *task)
> > +static int find_later_rq(struct task_struct *sched_ctx, struct task_st=
ruct *exec_ctx)
>
> Nit: line becomes too long. Same for find_later_rq()'s signature above
> as well as find_lowest_rq() in rt.c.

While I do try to keep things under 80 where I can, it's no longer the stan=
dard:
https://lore.kernel.org/lkml/20120203100743.GA3334@elte.hu/

> >
> > -     if (task->nr_cpus_allowed =3D=3D 1)
> > +     if (exec_ctx && exec_ctx->nr_cpus_allowed =3D=3D 1)
>
> Can exec_ctx be NULL? If so, we may hit a seg. fault at
> task_rq(exec_ctx) below.

Oh, this is a bad split on my part. Only after find_exec_ctx() is
introduced can the exec_ctx be null.
I'll move that change to later in the series.

thanks
-john