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From: Ingo Molnar <mingo@elte.hu>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Rob Landley <rob@landley.net>, linux-kernel@vger.kernel.org
Subject: Re: 2.6.24 says "serial8250: too much work for irq4" a lot.
Date: Thu, 7 Feb 2008 13:39:38 +0100	[thread overview]
Message-ID: <20080207123937.GC15647@elte.hu> (raw)
In-Reply-To: <47A8D00F.9040803@zytor.com>


* H. Peter Anvin <hpa@zytor.com> wrote:

>> (If it's a qemu issue, I can go bother them.  It's possible that qemu 
>> isn't delivering interrupts as often as it expects, since that's 
>> limited by the granularity of the host timer; I know the clock in 
>> qemu can run a bit slow because it only gets clock interrupts when 
>> the host system isn't too busy to schedule the emulator.  But this 
>> doesn't usually cause a problem.  I _think_ the message is just a 
>> "this should never happen" type warning, which is happening to me.  
>> But I break stuff. :)
>
> This is because Qemu spews data to the serial port without any rate 
> limiting; this causes the in-kernel serial port driver to think the 
> port is stuck.  The serial port emulation needs to make it possible to 
> drain the virtual FIFO every now and then, as opposed to filling it 
> again immediately.

actually, the way i solved it for qemu+KVM+paravirt was to just turn off 
this rather silly check in the serial driver if inside a paravirt guest. 
When we are emulated then the serial 'hardware' is totally reliable and 
we should just trust it. That way i never dropped a single bit of kernel 
log output again.

	Ingo

  reply	other threads:[~2008-02-07 12:40 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-05 20:55 Rob Landley
2008-02-05 21:07 ` H. Peter Anvin
2008-02-07 12:39   ` Ingo Molnar [this message]
2008-02-07 17:37     ` H. Peter Anvin
2008-02-07 20:13       ` Rob Landley
2008-02-07 20:53         ` H. Peter Anvin
2008-02-07 21:19         ` H. Peter Anvin
2008-02-08  7:04           ` Rob Landley

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