linux-kernel - Re: Pin-pointing the root of unusual application latencies

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Date:	Wed, 25 Jul 2007 15:20:05 +0200
From:	John Sigler <linux.kernel@...e.fr>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Pin-pointing the root of unusual application latencies

(Dropping oprofile-list@...ts.sourceforge.net)

Ingo Molnar wrote:

> John Sigler wrote:
> 
>>> With a pair of the following in the middle:
>>>
>>> softirq--4     0....  670us : call_rcu (rt_run_flush)
>>> softirq--4     0D..1  670us : __rcu_advance_callbacks (call_rcu)
> 
>> Any idea what went wrong in the above function trace? Why is the 
>> kernel spinning in circles that way?
> 
> does your test-app have higher priority than softirq--4 ?

PID 4 is [softirq-timer/0] and has priority 50 in SCHED_FIFO.
My process has priority 80 in SCHED_RR. It is waiting for IRQ10.

My user-space app has higher priority than everything except
PID 2 which is [posix_cpu_timer]

Is this a priority inversion issue?

Regards.
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