lkml.org 
[lkml]   [2007]   [Feb]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch 4/9] Remove the TSC synchronization on SMP machines
Date
On Tuesday 13 February 2007 18:09, Christoph Lameter wrote:
> On Tue, 13 Feb 2007, Arjan van de Ven wrote:
>
> > no quite the opposite. gettimeofday() currently is NOT monotonic
> > unfortunately. With this patchseries it actually has a better chance of
> > becoming that...
>
> It is monotonic on IA64 at least and we have found that subtle application
> bugs occur if it is not. IA64 (and other arches using time interpolation)
> can insure the monotoneity of time sources. Are you sure about this? I
> wonder why the new time of day subsystem does not have that?

Just to avoid spreading misinformation: modulo some new broken hardware
(which we always try to work around when found) i386/x86-64 gettimeofday
is monotonic. AFAIK on the currently known hardware it should be generally
ok.

However ntpd can always screw you up, but that's inherent in the design.

Safer in general is to use clock_gettime(CLOCK_MONOTONIC, ...) which guarantees
no interference from ntpd

-Andi
-
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: 2007-02-13 18:23    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site