lkml.org 
[lkml]   [2005]   [Jun]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: latency error (~2ms) with nanosleep
On 6/13/05, Chris Friesen <cfriesen@nortel.com> wrote:
> quade wrote:
> > Playing around with the (simple) measurement of latency-times
> > I noticed, that the systemcall "nanosleep" has always a minimal
> > latency from about ~2ms (haven't run it all night, so...). It
> > seems to be a systematical error.
>
> Known issue. The x86 interrupt usually has a period of slightly less
> than a ms. It will therefore generally add nearly a whole ms to ensure
> that it does not ever wait for *less* than specified.

Exactly. And the sys_nanosleep() code adds one more if the parameter
has any positive value at all:

expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec);
current->state = TASK_INTERRUPTIBLE;
expire = schedule_timeout(expire);

Thanks,
Nish
-
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: 2005-06-13 18:58    [W:0.057 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site