virtio-blk-pci: default num_queues to -smp N

Automatically size the number of virtio-blk-pci request virtqueues to
match the number of vCPUs.  Other transports continue to default to 1
request virtqueue.

A 1:1 virtqueue:vCPU mapping ensures that completion interrupts are
handled on the same vCPU that submitted the request.  No IPI is
necessary to complete an I/O request and performance is improved.  The
maximum number of MSI-X vectors and virtqueues limit are respected.

Performance improves from 78k to 104k IOPS on a 32 vCPU guest with 101
virtio-blk-pci devices (ioengine=libaio, iodepth=1, bs=4k, rw=randread
with NVMe storage).

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Message-Id: <20200818143348.310613-7-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 9ee2aa0f7b..7f65fa8743 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -31,6 +31,7 @@
 GlobalProperty hw_compat_5_1[] = {
     { "vhost-scsi", "num_queues", "1"},
     { "vhost-user-scsi", "num_queues", "1"},
+    { "virtio-blk-device", "num-queues", "1"},
     { "virtio-scsi-device", "num_queues", "1"},
 };
 const size_t hw_compat_5_1_len = G_N_ELEMENTS(hw_compat_5_1);