linux-kernel - Re: [RFC PATCH v3 10/10] sched/fair: Throttle CFS tasks on return to userspace

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Message-ID: <20240712170505.GU27299@noisy.programming.kicks-ass.net>
Date: Fri, 12 Jul 2024 19:05:05 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Valentin Schneider <vschneid@...hat.com>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Phil Auld <pauld@...hat.com>, Clark Williams <williams@...hat.com>,
	Tomas Glozar <tglozar@...hat.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Arnd Bergmann <arnd@...db.de>, Guo Ren <guoren@...nel.org>,
	Palmer Dabbelt <palmer@...osinc.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [RFC PATCH v3 10/10] sched/fair: Throttle CFS tasks on return to
 userspace

On Thu, Jul 11, 2024 at 03:00:04PM +0200, Valentin Schneider wrote:
> +static inline void task_throttle_cancel_work(struct task_struct *p, int dst_cpu)
> +{
> +       /*
> +	* The calling context may be holding p->pi_lock, which is also acquired
> +	* by task_work_cancel_match().
> +	*
> +	* Lock recursion is prevented by punting the work cancellation to the
> +	* next IRQ enable. This is sent to the destination CPU rather than
> +	* >this< CPU to prevent the task from resuming execution and getting
> +	* throttled in its return to userspace.
> +	*/


u're having white space trouble there.. :-)

> +       irq_work_queue_on(&p->unthrottle_irq_work, dst_cpu);
> +}