linux-kernel - Re: [PATCH V3 00/11] block-throttle: add .high limit

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Date:   Thu, 6 Oct 2016 10:04:41 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Paolo Valente <paolo.valente@...more.it>, Shaohua Li <shli@...com>,
        Vivek Goyal <vgoyal@...hat.com>, linux-block@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...com>, Kernel-team@...com,
        jmoyer@...hat.com, Mark Brown <broonie@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH V3 00/11] block-throttle: add .high limit

On Tue, Oct 4, 2016 at 9:14 PM, Tejun Heo <tj@...nel.org> wrote:

> I get that bfq can be a good compromise on most desktop workloads and
> behave reasonably well for some server workloads with the slice
> expiration mechanism but it really isn't an IO resource partitioning
> mechanism.

Not just desktops, also Android phones.

So why not have BFQ as a separate scheduling policy upstream,
alongside CFQ, deadline and noop?

I understand the CPU scheduler people's position that they want
one scheduler for everyone's everyday loads (except RT and
SCHED_DEADLINE) and I guess that is the source of the highlander
"there can be only one" argument, but note this:

kernel/Kconfig.preempt:

config PREEMPT_NONE
        bool "No Forced Preemption (Server)"
config PREEMPT_VOLUNTARY
        bool "Voluntary Kernel Preemption (Desktop)"
config PREEMPT
        bool "Preemptible Kernel (Low-Latency Desktop)"

We're already doing the per-usecase Kconfig thing for preemption.
But maybe somebody already hates that and want to get rid of it,
I don't know.

Yours,
Linus Walleij