linux-kernel - Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice

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Message-ID: <20250206135353.i1tp4vDv@linutronix.de>
Date: Thu, 6 Feb 2025 14:53:53 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Prakash Sangappa <prakash.sangappa@...cle.com>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ankur Arora <ankur.a.arora@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>, linux-mm@...ck.org,
	x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
	luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
	hpa@...or.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
	willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
	bharata@....com, raghavendra.kt@....com,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Konrad Wilk <konrad.wilk@...cle.com>, jgross@...e.com,
	Andrew.Cooper3@...rix.com, Vineeth Pillai <vineethrp@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Clark Williams <clark.williams@...il.com>, daniel.wagner@...e.com,
	Joseph Salisbury <joseph.salisbury@...cle.com>, broonie@...il.com
Subject: Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice

On 2025-02-06 14:48:59 [+0100], Peter Zijlstra wrote:
> On Thu, Feb 06, 2025 at 02:44:08PM +0100, Sebastian Andrzej Siewior wrote:
> > SCHED_OTHER vs SCHED_OTHER after all. But please don't delay a wakeup of
> > SCHED_FIFO/ RR/ DL because of this LAZY hint.
> 
> Thing will get delayed if interrupts are disabled or kernel has
> preemption disabled too. So as long as we ensure hint crap is of equal
> order, nothing cares if you do.
> 
> If you can't tell the difference between task does hint crap in
> userspace and task is in the middle of syscall, you can't tell the
> difference.

I can tell the difference if I see a trace where an interrupt fires,
performs a wakeup and the SCHED_OTHER task remains on CPU while the task
SCHED_FIFO task sits on the runqueue until a timer fires.

Sebastian