On 2021-09-11 18:46:57 (+0900), Takashi Sakamoto wrote:
> Hi,
> 
> On Fri, Sep 10, 2021 at 01:55:41PM +0200, Sebastian Andrzej Siewior wrote:
> > On 2021-09-08 11:17:18 [+0900], Takashi Sakamoto wrote:
> > > Hi,
> > Hi,
> > 
> > > According to the log, the task of 'pipewire-media-:2554' is blocked during
> > > 122 seconds by call of 'wait_for_completion()' in code of
> > > 'fw_run_transaction()'. This is odd in two points of transaction service
> > > programmed in Linux FireWire subsystem:
> > > 
> > > 1. The process context should be awakened by softIRQ context, which should
> > >    be scheduled by hwIRQ context for hardware interrupt of OHCI 1394
> > >    controller.
> > > 2. Even if the softIRQ context is not invoked, the process context
> > >    should be awakened by wheel timer context, which is scheduled to finish
> > >    the transaction several jiffies later (originally prepared for the case
> > >    of split-transaction). In the case, the result of transaction is
> > >    'RCODE_CANCELLED'.
> > 
> > 
> > Side note: David is using PREEMPT_RT and his problem can be reduced to
> > plain vanilla with `threadirqs' boot option. Back in February I sent him
> > a patch [0] which inlines the tasklet job as I assumed it is not good
> > reset the IRQ-event in the tasklet/workqueue. It seemed to improve the
> > situtation as it recognized the device attached to the bus but ended
> > then in the same timeout behaviour as now.
> > 
> > [0] https://https://lkml.kernel.org/r/.kernel.org/all/20210218083849.iitcrhdgv2oajfhv@linutronix.de/
> 
> Thanks for the side note, and I apologize to follow the thread partially,
> not entire.
> 
> Furthermore, I'd like to correct my misunderstanding about the 2nd point
> since the timer wheel context is scheduled only when the peer of
> transaction transfer ack_pending for the request subaction. Without the
> hwIRQ context, the task is blocked ever anyway.

Thanks at any rate to look into this! It is much appreciated!

Is there anything further I can try to debug this using threadirqs? It
would be really amazing to be able to use this device on PREEMPT_RT
again (especially given that now the ALSA driver has improved so
drastically). :)

Best,
David

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