linux-kernel - Re: [RFC/PATCH] PM / Sleep: Timer quiesce in freeze state

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Message-ID: <20141029082432.GV3337@twins.programming.kicks-ass.net>
Date:	Wed, 29 Oct 2014 09:24:32 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Brown, Len" <len.brown@...el.com>,
	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	"linux-pm@...r.kernel.org >> Linux PM list" 
	<linux-pm@...r.kernel.org>
Subject: Re: [RFC/PATCH] PM / Sleep: Timer quiesce in freeze state

On Wed, Oct 29, 2014 at 07:22:35AM +0800, Li, Aubrey wrote:
> On 2014/10/28 16:25, Peter Zijlstra wrote:
> > On Tue, Oct 28, 2014 at 03:52:17PM +0800, Li, Aubrey wrote:
> > 
> >> Both clocksource and clockevents are not per-cpu device, why do we need
> >> to run their suspend callback on *each* cpu?
> > 
> > Uhm, you mean to say we don't use per-cpu timer lists and per-cpu timer
> > hardware for clockevents then?
> > 
> 
> From OS level, currently tick device is per-cpu implementation while
> clocksource and clockevent devices are global device.
> 
> We already stop tick by clockevents_notify(suspend) on each cpu, that
> addresses per-cpu timer list.

Right, I know. But I was saying I might have confused myself between
events and sources while going through that call chain, thereby
(mistakenly) thinking the source suspend code needed more than the 1
cpu.

Its easy to confuse yourself trying to reverse engineer that opaque
callchain :-)

> And, we already call clocksource_suspend() and clockevents_suspend() in
> timekeeping_suspend() on the tick timer CPU. Yes, we didn't suspend
> per-cpu timer hardware on x86 because x86 does not have lapic timer
> suspend implementation. If we need to implement this, I think we can do
> the cross-CPU calls in clocksource/clockevents suspend(), but I didn't
> see any necessary we need to do this now.
> 
> so, I think we are okay now, :)

Right, I tend to agree, we'll find out quickly enough once those
platforms will try this code anyhow ;-)
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