linux-kernel - Re: Consider switching to WQ_UNBOUND messages (was: Re: [PATCH v2 6/7] workqueue: Report work funcs that trigger automatic CPU

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Message-ID: <CAMuHMdUMRS9_nJXp3rrWQrODRQcBQggze0k=0GjSScCknFmmgQ@mail.gmail.com>
Date:   Wed, 12 Jul 2023 11:04:16 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-team@...a.com, Linux PM list <linux-pm@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-rtc@...r.kernel.org,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        netdev <netdev@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        "open list:LIBATA SUBSYSTEM (Serial and Parallel ATA drivers)" 
        <linux-ide@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: Consider switching to WQ_UNBOUND messages (was: Re: [PATCH v2
 6/7] workqueue: Report work funcs that trigger automatic CPU_INTENSIVE mechanism)

Hoi Peter,

On Wed, Jul 12, 2023 at 10:05 AM Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Jul 11, 2023 at 11:39:17AM -1000, Tejun Heo wrote:
> > I wonder whether the right thing to do here is somehow scaling the threshold
> > according to the relative processing power. It's difficult to come up with a
> > threshold which works well across the latest & fastest and really tiny CPUs.
> > I'll think about it some more but if you have some ideas, please feel free
> > to suggest.
>
> We could scale by BogoMIPS I suppose, it's a bogus measurement, as per
> the name, but it does have some relation to how fast the machine is.

That's gonna fail miserably on e.g. ARM and RISC-V, where BogoMIPS
depends on some timer frequency.

R-Car M2-W with 1.5 GHz Cortex-A15: 40.00 BogoMIPS
R-Car V4H with 1.8 GHz Cortex-A76: 33.33 BogoMIPS

while the real slow 48 MHz VexRiscV gets 128 BogoMIPS.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds