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Subject: Re: [Fwd: Re: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0.4]
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Lee Revell <rlrevell@joe-job.com>
Cc: Ingo Molnar <mingo@elte.hu>, Florian Schmidt <mista.tapas@gmx.net>,
       Paul Davis <paul@linuxaudiosystems.com>,
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References: <20041031120721.GA19450@elte.hu>
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Organization: linutronix
Date: Mon, 01 Nov 2004 18:58:22 +0100
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On Mon, 2004-11-01 at 12:55 -0500, Lee Revell wrote:
> I think there might even be a _very_ rare errant irq disable in T3 even.
> On my 2-day test runs with 100s of millions of samples, I got 2 or 3
> outliers in each graph.  Jow Gwinn from LKML (thanks Joe) ran a
> statistical analysis that showed these to be independent from the 4 or 5
> underlying exponential distributions (each corresponding to a known or
> suspected nonpreemptible section).  Our theory was that these were very
> rare code paths or race conditions that left IRQs off.  Unfortunately
> this seems impossible to debug unless you have a way to make the machine
> crash dump immediately when it detects the situation.
> 
> Anyway, the clearest way to demonstrate the problem with the -V series
> here is to run the version of Florian's tool that tells you how many
> interrupts were missed.  If I spin my (USB, not sharing irq with
> soundcard) trackball as fast as I can I can get it up to 54 or 55 in a
> row.  If I move it just the right way I can see the humps appear - 2,
> then 15, then 50 then 15 then 2 missed interrupts in a row.  This is at
> 1024Hz - at 2048 I can get it to miss several hundred IRQs, but this
> inevitably locks the machine.
> 
> I suspect the lockups and the latencies are same bug.

Until now there was no output on lockup. No I got one.
The command was: cat /proc/interrupts

Hope that helps

tglx

cat/1488: BUG in down_mutex
at /work/thomas/Linux/2.6.9-mm1-RT/lib/rwsem-generic.c:1059
 [<c01ca9e2>] down_mutex+0x72/0x80 (8)
 [<c012db9a>] __mutex_lock+0x2a/0x40 (36)
 [<c012dbc7>] _mutex_lock+0x17/0x20 (12)
 [<c013fd62>] kfree+0x52/0xf0 (8)
 [<c013fd62>] kfree+0x52/0xf0 (4)
 [<c01774a2>] single_release+0x32/0x40 (32)
 [<c01571ba>] __fput+0x13a/0x150 (20)
 [<c0155899>] filp_close+0x59/0x90 (32)
 [<c015593f>] sys_close+0x6f/0xa0 (24)
 [<c010603b>] syscall_call+0x7/0xb (28)


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