linux-kernel - Re: [PATCH v3]PM/Sleep: Timer quiesce in freeze state

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Message-ID: <4090311.nIPlPBbS65@vostro.rjw.lan>
Date:	Mon, 26 Jan 2015 16:04:05 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Li, Aubrey" <aubrey.li@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Brown, Len" <len.brown@...el.com>,
	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v3]PM/Sleep: Timer quiesce in freeze state

On Monday, January 26, 2015 03:34:22 PM Thomas Gleixner wrote:
> On Mon, 26 Jan 2015, Rafael J. Wysocki wrote:
> > On Monday, January 26, 2015 03:24:27 PM Thomas Gleixner wrote:
> > > On Mon, 26 Jan 2015, Rafael J. Wysocki wrote:
> > > > On Monday, January 26, 2015 10:40:24 AM Thomas Gleixner wrote:
> > > > > The only remaining issue might be a NMI calling into
> > > > > ktime_get_mono_fast_ns() before timekeeping is resumed. Its probably a
> > > > > non issue on x86/tsc, but it might be a problem on other platforms
> > > > > which turn off devices, clocks, It's not rocket science to prevent
> > > > > that.
> > > > 
> > > > I don't see any users of ktime_get_mono_fast_ns() at all, unless some non-trivial
> > > > macros are involved.  At least grepping for it only returns the definition,
> > > > declarations and the line in trace.c.
> > > 
> > > You can trace in NMI and perf is going to use ktime_get_mono_fast_ns()
> > > eventually as well.
> > 
> > So I'm not sure how to intercept that to be honest.  Any hints?
> 
> If we suspend timekeeping we can make the fast timekeeper point at a
> dummy readout function which returns the time at suspend, if the clock
> source does not resume automagically.
> 
> As I said TSC should be a non issue, but other stuff might be. We
> could make it conditional on CLOCK_SOURCE_SUSPEND_NONSTOP perhaps.

OK, thanks!

Rafael

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