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Date: Tue, 04 Mar 2014 08:31:20 +0100 From: Mike Galbraith <bitbucket@...ine.de> To: Henrik Austad <henrik@...tad.us> Cc: John Stultz <johnstul@...ibm.com>, Salman Qazi <sqazi@...gle.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [RFC][PATCH] clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns() On Tue, 2014-03-04 at 08:20 +0100, Henrik Austad wrote: > On Tue, Mar 04, 2014 at 06:20:09AM +0100, Mike Galbraith wrote: > > Greetings, > > > > While rummaging around looking for HTH a gaggle of weird a$$ machines > > can manage to timewarp back and forth by exactly 208 days, I stumbled > > across $subject which looks like it may want to borrow Salman's fix. > > > > 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 <johnstul@...ibm.com> > > Signed-off-by: Mike Galbraith <bitbucket@...ine.de> > > --- > > include/linux/clocksource.h | 11 ++++++++--- > > 1 file changed, 8 insertions(+), 3 deletions(-) > > > > --- a/include/linux/clocksource.h > > +++ b/include/linux/clocksource.h > > @@ -77,13 +77,18 @@ struct timecounter { > > * > > * XXX - This could use some mult_lxl_ll() asm optimization. Same code > > * as in cyc2ns, but with unsigned result. > > + * > > + * Because it is the same as x86 __cycles_2_ns, give it the same treatment as > > + * commit 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock" > > + * to avoid a potential cycles * mult overflow. > > Do we normally reference a particular commit in a comment? Why not just > grab the same comment and add a "this is grabbed from arch/x86/... ? Fewer '+' signs? History doesn't go away, so seems fine to me. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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