LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: "H. Peter Anvin" <hpa@zytor.com>
To: Ingo Molnar <mingo@elte.hu>
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, 07 Feb 2008 09:37:12 -0800	[thread overview]
Message-ID: <47AB41C8.3010001@zytor.com> (raw)
In-Reply-To: <20080207123937.GC15647@elte.hu>

Ingo Molnar wrote:
> * 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.
> 

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

	-hpa

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=47AB41C8.3010001@zytor.com \
    --to=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@elte.hu \
    --cc=rob@landley.net \
    --subject='Re: 2.6.24 says "serial8250: too much work for irq4" a lot.' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).