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Date: Thu, 18 Nov 2004 16:44:42 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Adam Heath <adam@doogie.org>
Cc: linux-kernel@vger.kernel.org, Lee Revell <rlrevell@joe-job.com>,
       Rui Nuno Capela <rncbc@rncbc.org>, Mark_H_Johnson@Raytheon.com,
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       Shane Shrybman <shrybman@aei.ca>, Amit Shah <amit.shah@codito.com>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm1-V0.7.27-10
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* Adam Heath <adam@doogie.org> wrote:

> Running .26-5.  Been running almost 2 days.  All small latency values. 
> Then, just a few minutes ago, got a 133us value:

this entry has most of the overhead:

>     0 80000000 00000004 [0284618592175975] 0.000ms (+0.000ms): preempt_schedule+0x11/0x80 <c02bbb81> (__do_IRQ+0x13d/0x170 <c013f3cd>)
>     0 80000000 00000005 [0284618592176118] 0.000ms (+0.127ms): irq_exit+0xb/0x50 <c013f10b> (do_IRQ+0x53/0x70 <c01080d3>)
>     0 80000000 00000006 [0284618592387634] 0.127ms (+0.000ms): do_IRQ+0x0/0x70 <c0108080> (<0000a253>)
>     0 80000000 00000007 [0284618592387690] 0.127ms (+0.000ms): do_IRQ+0x0/0x70 <c0108080> (<0000000e>)

this shows that we interrupted some longer critical section - in this
case it seems to be BIOS/APM code.

> Note the jump in irq_exit/do_IRQ.

that jump is a delayed interrupt hitting the BIOS on its way out of APM
idle mode it seems:

>     0 80000000 0000001b [0284618592393899] 0.131ms (+0.000ms): apm_do_busy+0xb/0x40 <c01111eb> (cpu_idle+0x4c/0x70 <c0103f9c>)
>     0 80000000 0000001c [0284618592393987] 0.131ms (+0.000ms): apm_bios_call_simple+0xe/0xf0 <c0110f2e> (apm_do_busy+0x2e/0x40 <c011120e>)

There's nothing to be done about that, except to disable APM. Perhaps
you could try ACPI, maybe that doesnt have such latencies in the BIOS.

	Ingo
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