lkml.org 
[lkml]   [2006]   [Dec]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: realtime-preempt and arm

On Thu, 14 Dec 2006, tike64 wrote:

> Steven Rostedt <rostedt@goodmis.org> wrote:
> > ...
> > it's ok for the timer to be a little over, but it must never be a
> > little under.
> > ...
> > So we make sure the timer goes off in (n+1) ms, and not just (n).

Oops, that should have read (n+1) 10ms, or +1 res. But you got the point
anyway ;)

>
> Ok, this makes sense - thanks.
>
> What confuses / confused me is that I have 4 combinations:
> without-rt/with-rt X select/nanosleep; I first tried the
> without-rt/select combination and right after that with-rt combinations
> skipping the without-rt/nanosleep case. The first one was the one (the
> only one) which gives me the 10ms average delay. And after your
> explanations that fact bugs me even more.

Actually, I just ran your prog on a ia32 -rt kernel, with highres, and
using select, I get return times of less than 5ms. So this looks like a
bug. On 2.6.17 vanilla, I also got under 5ms. But it might be ok for
select to return early. I'm not sure on this one. But using nansleep
never returned early on either system.

>
> But that is a side issue. The real problem is now: how do I get rid of
> the multi-ms jitter?
>

So you got a big jitter using nanosleep??? If that's the case, could you
post the times you got. I'll also boot a kernel with the latest -rt patch,
without highres compiled, and see if I can reproduce the same on x86.

-- Steve

-
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: 2006-12-14 16:23    [W:0.045 / U:2.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site