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[Qemu-devel] Re: virtio-blk performance and MSI
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] Re: virtio-blk performance and MSI |
Date: |
Sun, 9 Aug 2009 22:56:42 +0300 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Sun, Aug 09, 2009 at 01:01:35PM +0300, Avi Kivity wrote:
> On 08/06/2009 07:35 PM, Christoph Hellwig wrote:
>> Michael suggested to me a while ago to try MSI with virtio-blk and I
>> played with this small patch:
>>
>>
>> Index: qemu-kvm/hw/virtio-blk.c
>> ===================================================================
>> --- qemu-kvm.orig/hw/virtio-blk.c
>> +++ qemu-kvm/hw/virtio-blk.c
>> @@ -416,6 +416,7 @@ VirtIODevice *virtio_blk_init(DeviceStat
>> s->vdev.get_config = virtio_blk_update_config;
>> s->vdev.get_features = virtio_blk_get_features;
>> s->vdev.reset = virtio_blk_reset;
>> + s->vdev.nvectors = 2;
some whitespace damage btw
>> s->bs = bs;
>> s->rq = NULL;
>> if (strlen(ps = (char *)drive_get_serial(bs)))
>>
>> which gave about 5% speedups on 4k sized reads and writes, see the full
>> iozone output I attached. Now getting the information about using
>> multiple MSI vectors from the command line to virtio-blk similar to how
>> virtio-net does seems extremly messy right now. Waiting for Gerd's
>> additional qdev patches to make it easier as a qdev property.
>>
>>
>
> Looks good. Anthony, I think this applies upstream?
This applies upstream, but we also need the flag to change # of vectors:
for loading old images, but also for troubleshooting.
Thus the qdev dependency.
--
MST