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

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Message-ID: <VI1PR04MB3039EB80F5468E55263ABECBF4390@VI1PR04MB3039.eurprd04.prod.outlook.com>
Date:   Fri, 1 Dec 2017 03:33:49 +0000
From:   Alison Wang <alison.wang@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Leo Li <leoyang.li@....com>
CC:     Arnd Bergmann <arnd@...db.de>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Huan Wang <alison.wang@...escale.com>,
        "Daniel Lezcano" <daniel.lezcano@...aro.org>,
        John Stultz <john.stultz@...aro.org>
Subject: RE: [PATCH] arm: kernel: utilize hrtimer based broadcast

Hi, Russell,

> 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.
> 
[Alison Wang] What's your opinion about this explanation? Is this patch acceptable?

Best Regards,
Alison Wang