From: Jan Kiszka <jan.kiszka@web.de>
To: Michael Tokarev <mjt@tls.msk.ru>
Cc: "René Pfeiffer" <lynx@luchs.at>, kvm@vger.kernel.org
Subject: Re: I/O performance of VirtIO
Date: Tue, 13 Oct 2009 08:35:36 +0200 [thread overview]
Message-ID: <4AD41FB8.6000209@web.de> (raw)
In-Reply-To: <4AD3A38D.3090102@msgid.tls.msk.ru>
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Michael Tokarev wrote:
> René Pfeiffer wrote:
>> Hello!
>>
>> I just tested qemu-kvm-0.11.0 with the KVM module of kernel 2.6.31.1. I
>> noticed that the I/O performance of an unattended stock Debian Lenny
>> install dropped somehow. The test machines ran with kvm-88 and 2.6.30.x
>> before. The difference is very noticeable (went from about 5 minutes up
>> to 15-25 minutes). The two test machines have different CPUs (one is an
>> Intel Core2 CPU, the other runs with an AMD Athlon 64 X2 Dual).
>>
>> Is this the effect of added code regarding caching/data integrity to the
>> VirtIO block layer or somewhere else? The qemu-system-x86_64 seems to
>> hang a lot more in heavy I/O (showing 'D' in top/htop).
>>
>> The command line is quite straight-forward:
>> qemu-system-x86_64 -drive file=debian.qcow2,if=virtio,boot=on -cdrom \
>> /srv/isos/debian-502-i386-netinst.iso -smp 2 -boot d -m 512 -net nic \
>> -net user -usb
> ^^^^^^^^^
>
> Care to try with something more real than user-level networking?
> You're using netinstall which - apparently - tries to use some
> networking d/loading components etc, and userlevel networking is
> known to be very very slow....
It can be particularly slow if you use in-kernel irqchips and the
default NIC emulation (up to 10 times slower), some effect I always
wanted to understand on a rainy day. So, when you actually want -net
user, try -no-kvm-irqchip.
Jan
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next prev parent reply other threads:[~2009-10-13 6:36 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-12 20:49 I/O performance of VirtIO René Pfeiffer
2009-10-12 21:45 ` Michael Tokarev
2009-10-12 21:54 ` René Pfeiffer
2009-10-13 6:35 ` Jan Kiszka [this message]
2009-10-22 16:29 ` Avi Kivity
2009-10-22 22:06 ` Alexander Graf
2009-10-25 5:44 ` Avi Kivity
2009-10-26 8:12 ` Jan Kiszka
2009-10-26 8:35 ` Avi Kivity
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