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.
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 <stefa...@redhat.com>
Reviewed-by: Cornelia Huck <coh...@redhat.com>
---
hw/block/virtio-blk.c | 6 +++++-
hw/core/machine.c | 1 +
hw/virtio/virtio-blk-pci.c | 9 ++++++++-
include/hw/virtio/virtio-blk.h | 2 ++
4 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 142863a3b2..ed5df71779 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -1135,6 +1135,9 @@ static void virtio_blk_device_realize(DeviceState *dev,
Error **errp)
error_setg(errp, "Device needs media, but drive is empty");
return;
}
+ if (conf->num_queues == VIRTIO_BLK_AUTO_NUM_QUEUES) {
+ conf->num_queues = 1;
+ }
if (!conf->num_queues) {
error_setg(errp, "num-queues property must be larger than 0");
return;
@@ -1271,7 +1274,8 @@ static Property virtio_blk_properties[] = {
#endif
DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
true),
- DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
+ DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues,
+ VIRTIO_BLK_AUTO_NUM_QUEUES),
DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 256),
DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 4bbcec8fbd..c993b8f489 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -31,6 +31,7 @@
GlobalProperty hw_compat_4_2[] = {
{ "virtio-blk-device", "queue-size", "128"},
{ "virtio-scsi-device", "virtqueue_size", "128"},
+ { "virtio-blk-device", "num-queues", "1"},
{ "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
{ "virtio-blk-device", "seg-max-adjust", "off"},
{ "virtio-scsi-device", "num_queues", "1"},
diff --git a/hw/virtio/virtio-blk-pci.c b/hw/virtio/virtio-blk-pci.c
index efb2c22a1d..bf628de675 100644
--- a/hw/virtio/virtio-blk-pci.c
+++ b/hw/virtio/virtio-blk-pci.c
@@ -17,6 +17,7 @@
#include "qemu/osdep.h"
+#include "hw/boards.h"
#include "hw/qdev-properties.h"
#include "hw/virtio/virtio-blk.h"
#include "virtio-pci.h"
@@ -50,9 +51,15 @@ static void virtio_blk_pci_realize(VirtIOPCIProxy *vpci_dev,
Error **errp)
{
VirtIOBlkPCI *dev = VIRTIO_BLK_PCI(vpci_dev);
DeviceState *vdev = DEVICE(&dev->vdev);
+ VirtIOBlkConf *conf = &dev->vdev.conf;
+
+ /* 1:1 vq to vcpu mapping is ideal because it avoids IPIs */
+ if (conf->num_queues == VIRTIO_BLK_AUTO_NUM_QUEUES) {
+ conf->num_queues = current_machine->smp.cpus;
+ }
if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
- vpci_dev->nvectors = dev->vdev.conf.num_queues + 1;
+ vpci_dev->nvectors = conf->num_queues + 1;
}
qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 1e62f869b2..4e5e903f4a 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -30,6 +30,8 @@ struct virtio_blk_inhdr
unsigned char status;
};
+#define VIRTIO_BLK_AUTO_NUM_QUEUES UINT16_MAX
+
struct VirtIOBlkConf
{
BlockConf conf;
--
2.24.1
