lkml.org 
[lkml]   [2008]   [Nov]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] Add round_jiffies_up and related routines
On Wed, Nov 05 2008, Alan Stern wrote:
> On Wed, 5 Nov 2008, Tejun Heo wrote:
>
> > Alan Stern wrote:
> > > This patch (as1158) adds round_jiffies_up() and friends. These
> > > routines work like the analogous round_jiffies() functions, except
> > > that they will never round down.
> > >
> > > The new routines will be useful for timeouts where we don't care
> > > exactly when the timer expires, provided it doesn't expire too soon.
> > >
> > > Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> >
> > Heh... I have exactly the same patches but mines were named
> > round_up_jiffies().
>
> To an American, "round_up_jiffies" sounds like something a cowboy might
> do. :-)
>
> I haven't bothered to look throughout the kernel to see where
> round_jiffies_up() could be used. Have you done this?

Heh, I do agree :-)

> > > + unsigned long j0 = jiffies;
> > > +
> > > + barrier(); /* Prevent the compiler from aliasing j0 and jiffies */
> > > + return round_jiffies_common(j + j0, cpu, false) - j0;
> >
> > jiffies is volatile. No need for explicit barrier,
>
> I didn't realize that. Good, it makes things easier.
>
> > but this part is
> > necessary for correct operation as if jiffies go up by two the
> > calculation will wrap and the returned value will be very large. I
> > think this fix deserves a separate patch and proper explanation.
>
> How about if I remove the barrier() call? Should this new code still
> go in a separate patch?

I think it's fine as-is without the barrier. Can you resend it as such,
makes it easier to merge up (plus, it does need a new signed-off-by).

--
Jens Axboe



\
 
 \ /
  Last update: 2008-11-05 20:15    [W:0.048 / U:2.912 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site