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[Qemu-devel] Re: virtio-blk performance and MSI

From: Avi Kivity
Subject: [Qemu-devel] Re: virtio-blk performance and MSI
Date: Sun, 09 Aug 2009 13:01:35 +0300
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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;
      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?

error compiling committee.c: too many arguments to function

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