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Date: Fri, 25 Nov 2005 14:55:33 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Schultheiss, Christoph" <Christoph.Schultheiss@eurocopter.com>,
       john stultz <johnstul@us.ibm.com>, linux-kernel@vger.kernel.org
Subject: Re: duration of udelay differs with activated realtime-preempt patch?
Message-ID: <20051125135533.GA12823@elte.hu>
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* Steven Rostedt <rostedt@goodmis.org> wrote:

> > after measuring the duration of the function udelay (with oscilloscope
> > at parallel port), I figured out that udelay (5usec) with activated
> > realtime- preempt patch lasts a little bit longer. Without the patch the
> > time is exact.
> > All kernel debug switches are turned off at compile time.
> > Can anyone suggest why this happens?
> 
> Well, the -rt patch, has changed the udelay function.  BTW, you are 
> using the constant udelay, right?  Maybe an example of the code you 
> used to test might be useful.
> 
> Ingo or John?

yes, i found this problem too, a week ago or so. It's due to the GTOD 
changes to i386's __delay() function. Does it still occur with -rt15 
[which has the -B11 GTOD patchset] ?

	Ingo