lkml.org 
[lkml]   [2006]   [Mar]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] simplify update_times (avoid jiffies/jiffies_64 aliasing problem)
Andrew Morton writes:
> Paul Mackerras <paulus@samba.org> wrote:
> >
> > Andi Kleen writes:
> >
> > > Also I assume Atsushi-san did the patch because he saw a real problem?
> >
> > Yes, one which I also saw on PPC. The compiler (gcc-4) emits loads
> > for jiffies, jiffies64 and wall_jiffies before storing the incremented
> > jiffies64 value back.
> >
>
> What was the effect of that?

The effect is that the first call to do_timer doesn't increment xtime.
This explains why the code I have to detect disagreements between
xtime and the time of day as computed from the timebase register was
finding a disagreement on the first tick, which I was scratching my
head over.

There may be other effects on architectures which use wall_jiffies to
detect lost timer ticks. We don't have that problem on PPC and we
don't use wall_jiffies in computing time of day.

Paul.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-03-04 13:36    [from the cache]
©2003-2011 Jasper Spaans