linux-kernel - Re: [PATCH] arm: kernel: utilize hrtimer based broadcast

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Message-ID: <CADRPPNTHyMUQ80EEB3dSOfWM2q4+HpPVKNVW9bnvXJV3rQuwrA@mail.gmail.com>
Date:   Tue, 2 Apr 2019 21:36:42 -0500
From:   Yang Li <pku.leo@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Russell King - ARM Linux <linux@....linux.org.uk>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Huan Wang <alison.wang@...escale.com>,
        Huan Wang <alison.wang@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        John Stultz <john.stultz@...aro.org>,
        LAK <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm: kernel: utilize hrtimer based broadcast

On Tue, Jan 5, 2016 at 3:46 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Sat, 2 Jan 2016, Russell King - ARM Linux wrote:
> > On Tue, Dec 29, 2015 at 02:54:10PM +0100, Thomas Gleixner wrote:
> > > I have no real opinion about that patch. It does no harm to unconditionally
> > > setup the hrtimer based broadcast even if it's never used.
> > >
> > > Up to the arch maintainer to decide.
> >
> > That's really not fair to keep shovelling these kinds of decisions onto
> > architecture maintainers without any kind of explanation about how an
> > architecture maintainer should make such a decision.
> >
> > Do I roll a 6-face dice, and if it gives an odd number, I apply this
> > patch, otherwise I reject it?
> >
> > Is there a technical basis for making the decision?  If so, please
> > explain what the technical arguments are against having or not having
> > this change.
>
> The hrtimer based broadcast device is used when you have per cpu timers which
> stop in deeper power states, but you have no other timer hardware on the chip
> which can backup the per cpu timer in deep power states. The trick is that it
> emulates a timer hardware via a hrtimer and then tells the cpu idle code not
> to go into deep power states on the cpu which owns that hrtimer. All other
> cpus can go as deep as they want and still get woken up.
>
> The only downside of adding this unconditionally is extra code in case that it
> is not needed on a particular platform.
>
> Hope that helps.

Hi Russell,

This has been pending for so long time.  I assume this is an ack from
Thomas.  And given the same thing has been added for arm64 and powerpc
architecture, can you also merge this for ARM?


Regards,
Leo