linux-kernel - Re: [PATCH v2 0/6] atmel_serial: Cleanups, irq handler splitup & DMA

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Date:	Wed, 19 Dec 2007 17:59:09 +0100
From:	"Remy Bohmer" <linux@...mer.net>
To:	"Haavard Skinnemoen" <hskinnemoen@...el.com>
Cc:	"Andrew Victor" <linux@...im.org.za>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	"Russell King" <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, kernel@...32linux.org
Subject: Re: [PATCH v2 0/6] atmel_serial: Cleanups, irq handler splitup & DMA

> > but I noticed that I sometimes get an input overrun (ttyS0: 1
> > input overrun(s) ) during stress conditions.
> > This is something I did not notice before, maybe it was already there,
> > or has something changed in this area that it is now more sensitive
> > for this?
> Hmm...is this with or without DMA?

DBGU is without DMA.

> If it's without DMA, something very strange is going on -- the non-DMA
> RX code is almost the only thing left in the hardirq handler, so I
> would really expect overruns to be much less likely to occur now than
> before...

As mentioned, maybe it was already there, but I did not run into it
earlier. I have to figure that out. But, at 115200 and a 1 byte
receive-'fifo' on DBGU, and still interrupt locks somewhere in the
tree up to 300us, it is a simple calculation that we can run into
overrun conditions...
Notice that without these interrupt handler splitup, it was much, much
much worse...

So, for me it is not a big deal, because it is just a terminal, and
with my shaky fingers I usually do not type that fast ;-))

Remy

Kind Regards,

Remy
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