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From: "H. Peter Anvin" <>
To: Ingo Molnar <>
Cc: Rob Landley <>,
Subject: Re: 2.6.24 says "serial8250: too much work for irq4" a lot.
Date: Thu, 07 Feb 2008 09:37:12 -0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Ingo Molnar wrote:
> * H. Peter Anvin <> 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.

Yes, but keying that on paravirt is silly in the extreme.  After all, 
there is no need for this to be paravirtualized.


  reply	other threads:[~2008-02-07 17:37 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
2008-02-07 17:37     ` H. Peter Anvin [this message]
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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