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

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Date:   Fri, 27 Oct 2023 12:44:19 -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 Fri, 27 Oct 2023 12:21:45 -0400
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> > Attached is the updated test program.  
> 
> I think you'll want to modify the semantic of your "cr_flags" field so
> it supports nested locks as well. You can change this cr_flags for a
> nesting counter. The "yield" bit could be one of the bits of that
> counter (e.g. lowest bit).

Hmm, yeah, we could just have it be: bit 0 set by the kernel, and allow
user space set any bit above that to say "I'm in a critical section". Then,
the kernel would do:

	if (cr_flags & ~1) // in critical section

and this would allow user space to us cr_flags as the nested counter if it
wants to. I just don't want that to be a kernel requirement, but allowing
*any* bit to be set above bit 0 would allow user space to decide that or
not.

> 
> Therefore extend() become add 0x2, and unextend() become a sub 0x2, and
> you can check the lowest bit for yield hint.

Right, that makes sense. I'll update that in the next version.

Thanks!

-- Steve