linux-kernel - Re: realtime-preempt and arm

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Message-ID: <20061214100055.GB19549@elte.hu>
Date:	Thu, 14 Dec 2006 11:00:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	tike64 <tike64@...oo.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: realtime-preempt and arm


* tike64 <tike64@...oo.com> wrote:

> Steven Rostedt <rostedt@...dmis.org> wrote:
> > Also, have you tried this with a nanosleep instead of a select.
> > Select's timeout is just that, a timeout. It's not suppose to be
> > accurate, as long as it doesn't expire early.  The reason I state
> > this, is that select uses a different mechanism than nanosleep, and
> > that can indeed affect the jitter.
> 
> Ok, understood; I tried this:
> 
> 	t = raw_timer();
> 	ts.tv_nsec = 5000000;
> 	ts.tv_sec = 0;
> 	nanosleep(&ts, 0);
> 	t = raw_timer() - t;
> 
> It is better but I still see 8ms occasional delays when listing 
> nfs-mounted directories onto FB. And, what is funny, also this version 
> makes the average delay 20ms as if it made the jiffy 20ms.

ARM has no high resolution timers support yet in the -rt tree.

	Ingo
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