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 <sq...@google.com>
> > Cc: John Stultz <johns...@us.ibm.com>
> > Signed-off-by: Mike Galbraith <bitbuc...@online.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
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