linux-kernel - Re: [PATCH] serial: remove "too much work for irq" printk

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Date:	Sun, 13 Jan 2008 23:03:27 +0100
From:	Pavel Machek <pavel@....cz>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Benjamin LaHaise <bcrl@...ck.org>, akpm@...l.org,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: remove "too much work for irq" printk

On Sat 2008-01-12 21:24:57, Alan Cox wrote:
> On Sat, 12 Jan 2008 15:15:43 -0500
> Benjamin LaHaise <bcrl@...ck.org> wrote:
> 
> > When using kvm with a serial console, the serial driver will print out 
> > "too much work for irq4" on any heavy activity (ie vi on a file repainting 
> > the terminal).  This message is entirely spurious, as output continues to 
> > work fine.  Remove the message as it corrupts screen output and is far too 
> > easy to trigger.
> 
> NAK. This is a qemu/kvm emulation bug. The real check is there to catched
> jammed IRQs and combined with the IRQ bug handling nowdays does actually
> do the intended job.
> 
> Our serial port code (correctly) interprets a continuous stream of bytes
> at an impossible bit rate as an error. KVM should be emulating to some
> extent at least the timing on serial interfaces or using a virtualised
> interface.

How can you tell apart impossible bit rate from really slow CPU, or
maybe just an SMI storm, or heavy busmaster DMA?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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