linux-kernel - Re: [GIT pull] Timer core updates for 4.16

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Message-ID: <CA+55aFxzm6fY396+Nh3mZm5BroW4ZQmh3gj0YLvg7nKs5qzQKg@mail.gmail.com>
Date:   Tue, 30 Jan 2018 10:11:10 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>
Subject: Re: [GIT pull] Timer core updates for 4.16

On Mon, Jan 29, 2018 at 10:30 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> These are in cases significant driver simplifications, but they also enable the
> real deal, the elimination of the hrtimer tasklet:
>
>  softirq: Remove tasklet_hrtimer
>
>    include/linux/interrupt.h | 25 -----------------------
>    kernel/softirq.c          | 51 -----------------------------------------------
>    2 files changed, 76 deletions(-)
>
> ... which is a pretty nice thing in itself even without the driver
> simplifications!
>
> Plus the _real_ secret motivation behind it all is the -rt kernel and
> CONFIG_PREEMPT_RT=y and the ability to push most of the hrtimer processing into
> softirq context - while it still keeps the main hrtimer machinery capable to run
> in hard-RT hardirq domain. Turns out it was possible to implement this duality via
> the softirq-hrtimers, with a good chunk of benefits to non-rt upstream as well.

So this is the kind of explanation that I would have liked in the
"please pull" (and that would have been great in the merge message).
Explaining not just the "what", but very much the "why".

Anyway, it's obviously pulled regardless, and I'm just pointing this
out for "maybe next time".

                  Linus