[Qemu-devel] virtio-blk performance and MSI

[Christoph Hellwig]

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.

results.combined
Description: Text document