linux-kernel - Help: tasklet blocked for >8msec

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Message-ID: <49CCFEBA.6060009@imap.cc>
Date:	Fri, 27 Mar 2009 18:28:42 +0200
From:	Tilman Schmidt <tilman@...p.cc>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Help: tasklet blocked for >8msec

A user of the Gigaset base driver (drivers/isdn/gigaset/bas-gigaset.c)
reports his connection being dropped exactly every 30 seconds.
Analysis of his dmesg indicates that when the error occurs, both the
tasklets read_iso_tasklet and write_iso_tasklet handling the B channel
data stream (125 USB isochronous packets per second in each direction)
are at the same time not executed for an entire inter-packet interval,
ie. 8 msecs.

The machine in question, an Intel Core2 Duo E8600 with 4 GB RAM and
SATA hard disks, should really be fast enough. CPU load is negligible.
I have asked the user to recompile the kernel with CONFIG_PREEMPT=y
and to replace the calls to schedule_tasklet() for the two tasklets
by schedule_hi_tasklet(). That had no noticeable effect on the problem.

I would be grateful for any hint on what could be the cause for that
blockage and how to prevent it.

aTdHvAaNnKcSe
Tilman

-- 
Tilman Schmidt                    E-Mail: tilman@...p.cc
Bonn, Germany
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