linux-kernel - Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice

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Date:   Thu, 26 Oct 2023 17:35:27 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-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, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.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@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com,
        Joel Fernandes <joel@...lfernandes.org>,
        Youssef Esmat <youssefesmat@...omium.org>,
        Vineeth Pillai <vineethrp@...gle.com>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...nel.org>
Subject: Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice

On Thu, 26 Oct 2023 15:20:22 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> Anyway, I changed the code to use:
> 
> static inline unsigned clrbit(volatile unsigned *ptr)
> {
> 	unsigned ret;
> 
> 	asm volatile("andb %b1,%0"
> 		     : "+m" (*(volatile char *)ptr)
> 		     : "iq" (0x2)
> 		     : "memory");
> 
> 	ret = *ptr;
> 	*ptr = 0;
> 
> 	return ret;
> }

Mathieu also told me that glibc's rseq has some extra padding at the end,
that happens to be big enough to hold this feature. That means you can run
the code without adding:

  GLIBC_TUNABLES=glibc.pthread.rseq=0

Attached is the updated test program.

-- Steve

View attachment "extend-sched.c" of type "text/x-c++src" (5906 bytes)