linux-kernel - Re: [PATCH v16 1/7] sched: Add CONFIG_SCHED_PROXY

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Message-ID: <CANDhNCocQLnYxzYYv17prsm7iJSE5032o_00XR0t8d1=gB4CVw@mail.gmail.com>
Date: Wed, 16 Apr 2025 14:24:06 -0700
From: John Stultz <jstultz@...gle.com>
To: Juri Lelli <juri.lelli@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Joel Fernandes <joelagnelf@...dia.com>, 
	Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Valentin Schneider <vschneid@...hat.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, 
	Zimuzo Ezeozue <zezeozue@...gle.com>, Mel Gorman <mgorman@...e.de>, Will Deacon <will@...nel.org>, 
	Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Metin Kaya <Metin.Kaya@....com>, 
	Xuewen Yan <xuewen.yan94@...il.com>, K Prateek Nayak <kprateek.nayak@....com>, 
	Thomas Gleixner <tglx@...utronix.de>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Suleiman Souhlal <suleiman@...gle.com>, kernel-team@...roid.com
Subject: Re: [PATCH v16 1/7] sched: Add CONFIG_SCHED_PROXY_EXEC & boot
 argument to enable/disable

On Mon, Apr 14, 2025 at 1:50 AM Juri Lelli <juri.lelli@...hat.com> wrote:
> On 11/04/25 23:02, John Stultz wrote:
> > Add a CONFIG_SCHED_PROXY_EXEC option, along with a boot argument
> > sched_proxy_exec= that can be used to disable the feature at boot
> > time if CONFIG_SCHED_PROXY_EXEC was enabled.
> >
> > Cc: Joel Fernandes <joelagnelf@...dia.com>
> > Cc: Qais Yousef <qyousef@...alina.io>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Juri Lelli <juri.lelli@...hat.com>
> > Cc: Vincent Guittot <vincent.guittot@...aro.org>
> > Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> > Cc: Valentin Schneider <vschneid@...hat.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Ben Segall <bsegall@...gle.com>
> > Cc: Zimuzo Ezeozue <zezeozue@...gle.com>
> > Cc: Mel Gorman <mgorman@...e.de>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Waiman Long <longman@...hat.com>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: "Paul E. McKenney" <paulmck@...nel.org>
> > Cc: Metin Kaya <Metin.Kaya@....com>
> > Cc: Xuewen Yan <xuewen.yan94@...il.com>
> > Cc: K Prateek Nayak <kprateek.nayak@....com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> > Cc: Suleiman Souhlal <suleiman@...gle.com>
> > Cc: kernel-team@...roid.com
> > Tested-by: K Prateek Nayak <kprateek.nayak@....com>
> > Signed-off-by: John Stultz <jstultz@...gle.com>
> > ---
>
> ...
>
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 47972f34ea701..154f0aa0c6322 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -1149,10 +1149,15 @@ struct rq {
> >        */
> >       unsigned int            nr_uninterruptible;
> >
> > +#ifdef CONFIG_SCHED_PROXY_EXEC
> > +     struct task_struct __rcu        *donor;  /* Scheduling context */
> > +     struct task_struct __rcu        *curr;   /* Execution context */
> > +#else
> >       union {
> >               struct task_struct __rcu *donor; /* Scheduler context */
> >               struct task_struct __rcu *curr;  /* Execution context */
> >       };
> > +#endif
> >       struct sched_dl_entity  *dl_server;
> >       struct task_struct      *idle;
> >       struct task_struct      *stop;
> > @@ -1347,10 +1352,17 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
> >  #define cpu_curr(cpu)                (cpu_rq(cpu)->curr)
> >  #define raw_rq()             raw_cpu_ptr(&runqueues)
> >
> > +#ifdef CONFIG_SCHED_PROXY_EXEC
> > +static inline void rq_set_donor(struct rq *rq, struct task_struct *t)
> > +{
> > +     rcu_assign_pointer(rq->donor, t);
> > +}
> > +#else
> >  static inline void rq_set_donor(struct rq *rq, struct task_struct *t)
> >  {
> >       /* Do nothing */
> >  }
> > +#endif
>
> Does this chunk belong here?

Uhm. It's there intentionally (as with the config option we actually
have the potential for the two contexts to be different), but I'm open
to move it elsewhere if you think it sticks out oddly here and would
fit better in a later change.

Maybe, would adding a note in the commit message to clarify that this
patch also adds the ability for the donor and curr contexts to be
different, help?

thanks
-john