From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michael Tokarev <mjt@tls.msk.ru>
Subject: kvm guest: hrtimer: interrupt too slow
Date: Tue, 29 Sep 2009 17:12:17 +0400
Message-ID: <4AC207B1.7020901@msgid.tls.msk.ru>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
To: kvm <kvm@vger.kernel.org>
Return-path: <kvm-owner@vger.kernel.org>
Received: from isrv.corpit.ru ([81.13.33.159]:44321 "EHLO isrv.corpit.ru"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751599AbZI2NMR (ORCPT <rfc822;kvm@vger.kernel.org>);
	Tue, 29 Sep 2009 09:12:17 -0400
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

Hello.

I'm having quite an.. unusable system here.
It's not really a regresssion with 0.11.0,
it was something similar before, but with
0.11.0 and/or 2.6.31 it become much worse.

The thing is that after some uptime, kvm
guest prints something like this:

hrtimer: interrupt too slow, forcing clock min delta to 461487495 ns

after which system (guest) speeed becomes
very slow.  The above message is from
2.6.31 guest running wiht 0.11.0 & 2.6.31
host.  Before I tried it with 0.10.6 and
2.6.30 or 2.6.27, and the delta were a
bit less than that:

hrtimer: interrupt too slow, forcing clock min delta to 152222415 ns
hrtimer: interrupt too slow, forcing clock min delta to 93629025 ns

etc.

Before, guest was just somewhat slow.  But
now, it reached the state when it's almost
unusable.

Especially "nice" it's visible in xterm
(running on that guest): typing a single
char in xterm results in it being displayed
after 1..2 sec pause.  With applications
like web browser (where all the font
rendering is done on the client and X
server receives bitmap instead of a
character code to draw, it isn't that
bad.

I suspect it's only happening with small
network packets.

The above message (with large min delta)
occured after about 20 hours uptime.  Similar
(give or take) delays were observed previously
as well.  That to say, -- it's not something
you notice immediately.

The problem is quite consistent, that is,
different guests shows it sooner or later.

Right now I'm running 2.6.31-amd64 host,
32bit qemu-kvm-0.11.0, 2.6.31-i686 uniprocessor
guest, virtio networking and block devices,
kvm-clock is enabled.  Similar configuration
were used before (with different versions).
The hardware is Phenom 9750 (4core) running
on Amd780g/sb700 chipset.

Any hints on what to do with all this?

Thanks!

/mjt