Re: [PATCH] clocksource_cyc2ns: avoid overflowing 64 bits

[Chris Metcalf]

On 11/16/2016 3:00 PM, John Stultz wrote:
> On Wed, Nov 16, 2016 at 11:56 AM, Chris Metcalf <cmetcalf@xxxxxxxxxxxx> wrote:
> > 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?
> Yea. Not many mailers can be trusted with sending patches. I'd
> recommend git-send-email. :)

Yes, indeed.  That is what I always do normally.  But since I was
already part way through an email written interactively in my mailer,
I figured I'd be lazy and paste it in.  Lesson learned...

That said, it is annoyingly difficult to pick up an in-progress email
and convert it into something you can edit in, say, Emacs.  You end up
having to cut and paste the "To:" and "Cc:" and "Subject:" information
out of your mailer's helpful GUI and into Emacs in the standard RFC822
way that git send-email understands.  I'm not sure there's a better
way, but at least I feel better now that I've complained about it :-)

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