linux-kernel - Re: [PATCH 3/3] sched/core: Indicate a sched_delayed task was migrated before wakeup

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Message-ID: <20241011103958.GO17263@noisy.programming.kicks-ass.net>
Date: Fri, 11 Oct 2024 12:39:58 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: K Prateek Nayak <kprateek.nayak@....com>,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	linux-kernel@...r.kernel.org,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Klaus Kudielka <klaus.kudielka@...il.com>,
	Chris Bainbridge <chris.bainbridge@...il.com>,
	"Linux regression tracking (Thorsten Leemhuis)" <regressions@...mhuis.info>,
	"Gautham R. Shenoy" <gautham.shenoy@....com>,
	Youssef Esmat <youssefesmat@...gle.com>,
	Paul Menzel <pmenzel@...gen.mpg.de>,
	Bert Karwatzki <spasswolf@....de>, regressions@...ts.linux.dev
Subject: Re: [PATCH 3/3] sched/core: Indicate a sched_delayed task was
 migrated before wakeup

On Fri, Oct 11, 2024 at 06:08:03AM -0400, Johannes Weiner wrote:

> Something like this?

Yeah, something like that indeed :-)

> I like it better too. There is a weird asymmetry between passing
> ENQ_MIGRATED to one and !ENQ_SLEEP to the other both as "migrate".

So I have a note to stare at the whole {EN,DE}QUEUE_MIGRATING,
ENQUEUE_MIGRATED and task_on_rq_migrating() situation, it has the
feeling that something could be done to clean up there.

> No strong preference for whether the ENQUEUE_RESTORE check should be
> in caller or callee, but I figured if we pass the flags anyway...

Right, and this way it's behind the static key, so win, right :-)

> I toyed with a separate branch for ENQUEUE_INITIAL. But it saves one
> branch during fork while adding one to repeat enqueues. The latter
> should be hotter on average, so I removed it again.
> 
> Completely untested. But if it looks good, I'll send a proper patch.

Sure. Thanks for doing this.