Re: [PATCH] clocksource_cyc2ns: avoid overflowing 64 bits

[Chris Metcalf]

On 11/16/2016 2:45 PM, John Stultz wrote:
> On Wed, Nov 16, 2016 at 11:30 AM, Chris Metcalf <cmetcalf@xxxxxxxxxxxx> wrote:
> > diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> > index 08398182f56e..5444429884b8 100644
> > --- a/include/linux/clocksource.h
> > +++ b/include/linux/clocksource.h
> > @@ -171,6 +171,10 @@ static inline u32 clocksource_hz2mult(u32 hz, u32
> > shift_constant)
> >    *
> >    * Converts cycles to nanoseconds, using the given mult and shift.
> >    *
> > + * The code is optimized for performance and not intended to work
> > + * with absolute clocksource cycles, as it will easily overflow,
> > + * but just intended for relative (delta) clocksource cycles.
> > + *
> >    * XXX - This could use some mult_lxl_ll() asm optimization
> Just as a heads up, it seems your working against an older kernel, as
> this didn't apply. Its simple enough to fix up, so I'll do so, but in
> the future, please submit patches against something close to Linus
> HEAD.

Oops, sorry; it wasn't version skew (I'm at v4.9-rc4) but whitespace damage.
I assumed if I just pasted the patch into Thunderbird it would work, since it had
no tabs.  But bizarrely, if I look at the patch in the mailer, it shows a two-space
prefix, but when I save the email to a file, it has a three-space prefix.  WTF?

--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com