linux-kernel - Re: [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler

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Message-ID: <3efb10970802041144j6b4e6893j293819238b5b82e8@mail.gmail.com>
Date:	Mon, 4 Feb 2008 20:44:51 +0100
From:	"Remy Bohmer" <linux@...mer.net>
To:	"Haavard Skinnemoen" <hskinnemoen@...el.com>
Cc:	michael <trimarchi@...dalf.sssup.it>, fabio@...dalf.sssup.it,
	"Andrew Victor" <linux@...im.org.za>,
	"Chip Coldwell" <coldwell@...hat.com>,
	"Marc Pignat" <marc.pignat@...s.ch>,
	"David Brownell" <david-b@...bell.net>,
	linux-kernel@...r.kernel.org, "Alan Cox" <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler

Hello Haavard,

> That's what I was thinking too. If this is indeed the cause, the
> dev_err() added by the debug patch I posted should trigger and we may
> consider boosting the priority of the tasklet (using
> tasklet_hi_schedule.)

Notice that we are talking about Preempt-RT here. Everything is
running in thread context, even tasklets, softirqs etc. They are _all_
preemptible, and if Michael has some RT-thread in the system that has
a higher priority than this tasklet or softirq, than the buffer will
eventually overflow.
I wonder also if Michael has set the RT-priorities correctly, on RT
_every_ softirq/irq thread starts by default on priority 50,
SCHED_FIFO. If they are still at 50, any other softirq/tasklet, or irq
can make this behavior worse.
Notice that the default 50 thingy rarely gives a decent behaving
system. (But any other default will also give problems anyway, so it
_has_ to be customized/tuned by the end user)

Kind Regards,

Remy
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