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

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Message-ID: <20250210144321.1f5974a6@gandalf.local.home>
Date: Mon, 10 Feb 2025 14:43:21 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Joel Fernandes <joel@...lfernandes.org>, Prakash Sangappa
 <prakash.sangappa@...cle.com>, Peter Zijlstra <peterz@...radead.org>,
 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 Thu, 6 Feb 2025 14:44:08 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> I did add a scheduling point in rt_spin_unlock() if LAZY was set and
> based on few tests it was something between noise and worse. It seems
> that "run to completion" is better than interrupt the kernel in the
> middle whatever it is doing. "Don't preempt the lock owner" is already
> handled by LAZY with the scheduling point on return to userland.

Does that mean that PREEMPT_RT requires a non preempt method for
SCHED_OTHER for SCHED_OTHER to not hit the issues that we were originally
hitting? That is, with being able to preempt spin_locks in PREEMPT_RT,
running a system with PREEMPT_RT in full preemption mode will still suffer
performance issues against a non PREEMPT_RT running in full preemption mode?

-- Steve