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

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Message-ID: <20231030094508.031357b4@gandalf.local.home>
Date:   Mon, 30 Oct 2023 09:45:08 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ankur Arora <ankur.a.arora@...cle.com>, 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 Mon, 30 Oct 2023 08:56:50 -0400
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
> This only works if "your" lock implementation is the only user of this 
> RSEQ feature within a process. RSEQ requires that multiple libraries can 
> share the facilities. Therefore, the rseq field should include the 
> nesting counter as part of the RSEQ ABI so various userspace libraries 
> can use it collaboratively.
> 

Then I would suggest allowing bit 31 be an "on/off" switch, and the lower
bits to be a counter. When I first tried this with postgres, there was one
lwlock that looked to be held for the majority of the run, so I got rid of
the nesting. But I think a mixture of both would work, where you can have a
nesting counter and an on/off switch with the caveat that if you use it and
enable it, another library may disable it.

-- Steve