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: <20230712122745.GH3100107@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Jul 2023 14:27:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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)

On Wed, Jul 12, 2023 at 11:04:16AM +0200, Geert Uytterhoeven wrote:
> 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.

Hehe, OK, really bogus then. Lets file this idea in the bit-bucket then.