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Subject: Re: [PATCH] 2.6.17-rt add clockevent to ixp4xx
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Daniel Walker <dwalker@mvista.com>
Cc: Milan Svoboda <msvoboda@ra.rockwell.com>, linux-kernel@vger.kernel.org,
       mingo@redhat.com
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Date: Thu, 13 Jul 2006 21:07:54 +0200
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On Thu, 2006-07-13 at 07:41 -0700, Daniel Walker wrote:
> On Thu, 2006-07-13 at 10:53 +0000, Milan Svoboda wrote:
> > Hello,
> > 
> > there are patches that enable clock event on ixp4xx platform. This should
> > enable high resolution timers... Option for hrtimers in menuconfig is 
> > also enabled.
> > 
> > I tested it on nanosleep test program (included in attachments) and obtained
> > this results:
> > 
> > requested: 899000 us, got: 899159 us, diff: -159 us
> > requested: 897000 us, got: 897209 us, diff: -209 us
> > requested: 895000 us, got: 899803 us, diff: -4803 us
> > requested: 893000 us, got: 899425 us, diff: -6425 us
> > requested: 891000 us, got: 899806 us, diff: -8806 us
> > requested: 889000 us, got: 890142 us, diff: -1142 us
> > requested: 887000 us, got: 889873 us, diff: -2873 us
> > requested: 885000 us, got: 888096 us, diff: -3096 us
> 
> I'd turn off some of the debugging options, and retest. For instance,
> the pi-list debugging option will cause arbitrary latency, which you
> seem to show in your results. Normally with PREEMPT_RT turned on you
> would expect the timers to trigger within a constant amount of time from
> when they are suppose to.

No, the time differences looks like the high res mode never gets
switched on. its oszillating between 0 and 10ms, which is the usual
behaviour for a non hrt kernel.

Also I would recommend to test without preempt-rt in the first place.
Preempt-rt on ARM is not really well tested, so you dont fight two
battles at once.

	tglx