linux-kernel - Re: [RFC][PATCH] clocksource: avoid unnecessary overflow in cyclecounter

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Date:	Tue, 04 Mar 2014 08:10:11 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	John Stultz <john.stultz@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"Cc: Salman Qazi" <sqazi@...gle.com>
Subject: Re: [RFC][PATCH] clocksource: avoid unnecessary overflow in
 cyclecounter_cyc2ns()

On Tue, 2014-03-04 at 14:40 +0800, John Stultz wrote: 
> On Tue, Mar 4, 2014 at 1:38 PM, Mike Galbraith <bitbucket@...ine.de> wrote:
> > (crap crap crap... M.A.I.N.T.A.I.N.E.R.S _dummy_)
> >
> > clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns()
> >
> > As per 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock",
> > cycles * mult >> shift is overflow prone. so give it the same treatment.
> >
> > Cc: Salman Qazi <sqazi@...gle.com>
> > Cc: John Stultz <john.stultz@...aro.org>,
> > Signed-off-by: Mike Galbraith <bitbucket@...ine.de>
> 
> Thanks for sending this in!  Curious exactly how the issue was being
> triggered?

Dunno that it is.  This is the result of me rummaging around, looking
for any excuse what-so-ever for a small and identical group of weird a$$
boxen running old 2.6.32 kernels (w. 208 day fix!) to manage to hop back
and forth in time by exactly 208 days.  Grep showed me that function, so
I scurried off and swiped the fix.

-Mike

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