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Date: Tue, 5 Dec 2006 09:25:53 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Karsten Wiese <fzu@wemgehoertderstaat.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: v2.6.19-rt1, yum/rpm
Message-ID: <20061205082553.GA13000@elte.hu>
References: <20061130083358.GA351@elte.hu> <200612050119.59113.fzu@wemgehoertderstaat.de>
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* Karsten Wiese <fzu@wemgehoertderstaat.de> wrote:

> I tweaked latency_trace.c to make freerunning work. Will post later.

ok, please do.

i'm trying to understand your trace:

> Below the trace shows i_usX2Y_usbpcm_urb_complete() running under an 
> alien context, and this is where jackd starts stalling:

by 'alien context' do you mean softirq--4? That is the following kernel 
thread:

    4 ?        S      0:00 [softirq-high/0]

handling HI_SOFTIRQ softirqs, which are the 'highprio' tasklets.

>   IRQ_17-308   0D..2 3411063us : deactivate_task <IRQ_17-308> (180 2)
> softirq--4     0D..2 3411064us+: __schedule <IRQ_17-308> (180 101)
> softirq--4     0.... 3411072us+: i_usX2Y_usbpcm_urb_complete (8 0 dd134)
> softirq--4     0.... 3411078us : try_to_wake_up (c011b4ab 0 0)
> softirq--4     0D..1 3411079us : __activate_task <jackd-2667> (173 1)
> softirq--4     0Dn.1 3411079us : try_to_wake_up <jackd-2667> (173 101)
> softirq--4     0Dn.1 3411080us : __schedule (c032a862 0 0)
>    jackd-2667  0D..2 3411081us+: __schedule <softirq--4> (101 173)

it's running at SCHED_FIFO prio 80.

it's probably this use in sound/usb/usbmidi.c:

                tasklet_hi_schedule(&port->ep->tasklet);

so what is your observation - if i_usX2Y_usbpcm_urb_complete() is 
executed in this tasklet then you are seeing xruns/delays?

	Ingo
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