From: Avi Kivity <avi@redhat.com>
To: Lucas Nussbaum <lucas@lucas-nussbaum.net>
Cc: john cooper <john.cooper@redhat.com>,
john cooper <john.cooper@third-harmonic.com>,
kvm@vger.kernel.org
Subject: Re: bad virtio disk performance
Date: Tue, 28 Apr 2009 14:55:42 +0300 [thread overview]
Message-ID: <49F6EEBE.6030601@redhat.com> (raw)
In-Reply-To: <20090428114849.GA12268@xanadu.blop.info>
Lucas Nussbaum wrote:
> On 28/04/09 at 12:56 +0200, Lucas Nussbaum wrote:
>
>> I then upgraded to kvm-85 (both the host kernel modules and the
>> userspace), and re-ran the tests. Performance is better (about 85 MB/s),
>> but still very far from the non-virtio case.
>>
>
> I forgot to mention that the strangest result I got was the total amount
> of write blocks queued (as measured by blktrace). I was writing a 1 GB
> file to disk, which resulted in:
>
> - 1 GB of write blocks queued without virtio
> - ~1.7 GB of write blocks queued with virtio on kvm 84
> - ~1.4 GB of write blocks queued with virtio on kvm 85
>
> I don't understand with kvm with virtio writes "more blocks than
> necessary", but that could explain the performance difference.
>
Are these numbers repeatable?
Try increasing the virtio queue depth. See the call to
virtio_add_queue() in qemu/hw/virtio-blk.c.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2009-04-28 11:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-27 15:12 bad virtio disk performance Lucas Nussbaum
2009-04-27 17:36 ` john cooper
2009-04-27 18:28 ` Lucas Nussbaum
2009-04-27 23:40 ` john cooper
2009-04-28 10:56 ` Lucas Nussbaum
2009-04-28 11:48 ` Lucas Nussbaum
2009-04-28 11:55 ` Avi Kivity [this message]
2009-04-28 14:35 ` Lucas Nussbaum
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