[Qemu-devel] [PATCH 5/5] virtio-net: Switch default to new bottom half TX handler for iothread

[Alex Williamson <alex.williamson@redhat.com>]

The bottom half handler shows big improvements over the timer
with few downsides, default to it when the iothread is enabled.

Using the following tests, with the guest and host connected
via tap+bridge:

guest> netperf -t TCP_STREAM -H $HOST
host> netperf -t TCP_STREAM -H $GUEST
guest> netperf -t UDP_STREAM -H $HOST
host> netperf -t UDP_STREAM -H $GUEST
guest> netperf -t TCP_RR -H $HOST

Results: base throughput, exits/throughput ->
                   patched throughput, exits/throughput

--enable-io-thread
TCP guest->host 2737.77, 47.82  -> 6767.09, 29.15 = 247%, 61%
TCP host->guest 2231.33, 74.00  -> 4125.80, 67.61 = 185%, 91%
UDP guest->host 6281.68, 14.66  -> 12569.27, 1.98 = 200%, 14%
UDP host->guest 275.91,  289.22 -> 264.80, 293.53 = 96%, 101%
interations/s   1949.65, 82.97  -> 7417.56, 84.31 = 380%, 102%

No --enable-io-thread
TCP guest->host 3041.57, 55.11 -> 1038.93, 517.57 = 34%, 939%
TCP host->guest 2416.03, 76.67 -> 5655.92, 55.52  = 234%, 72%
UDP guest->host 12255.82, 6.11 -> 7775.87, 31.32  = 63%, 513%
UDP host->guest 587.92, 245.95 -> 611.88, 239.92  = 104%, 98%
interations/s   1975.59, 83.21 -> 8935.50, 88.18  = 452%, 106%

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

 hw/s390-virtio-bus.c |    3 ++-
 hw/syborg_virtio.c   |    3 ++-
 hw/virtio-pci.c      |    3 ++-
 hw/virtio.h          |    6 ++++++
 4 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/hw/s390-virtio-bus.c b/hw/s390-virtio-bus.c
index 1483362..985f99a 100644
--- a/hw/s390-virtio-bus.c
+++ b/hw/s390-virtio-bus.c
@@ -328,7 +328,8 @@ static VirtIOS390DeviceInfo s390_virtio_net = {
     .qdev.size = sizeof(VirtIOS390Device),
     .qdev.props = (Property[]) {
         DEFINE_NIC_PROPERTIES(VirtIOS390Device, nic),
-        DEFINE_PROP_UINT32("txtimer", VirtIOS390Device, txtimer, 1),
+        DEFINE_PROP_UINT32("txtimer", VirtIOS390Device, txtimer,
+                           TXTIMER_DEFAULT),
         DEFINE_PROP_INT32("txburst", VirtIOS390Device, txburst, 256),
         DEFINE_PROP_END_OF_LIST(),
     },
diff --git a/hw/syborg_virtio.c b/hw/syborg_virtio.c
index 7b76972..ee5746d 100644
--- a/hw/syborg_virtio.c
+++ b/hw/syborg_virtio.c
@@ -300,7 +300,8 @@ static SysBusDeviceInfo syborg_virtio_net_info = {
     .qdev.props = (Property[]) {
         DEFINE_NIC_PROPERTIES(SyborgVirtIOProxy, nic),
         DEFINE_VIRTIO_NET_FEATURES(SyborgVirtIOProxy, host_features),
-        DEFINE_PROP_UINT32("txtimer", SyborgVirtIOProxy, txtimer, 1),
+        DEFINE_PROP_UINT32("txtimer", SyborgVirtIOProxy, txtimer,
+                           TXTIMER_DEFAULT),
         DEFINE_PROP_INT32("txburst", SyborgVirtIOProxy, txburst, 256),
         DEFINE_PROP_END_OF_LIST(),
     }
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index e025c09..9740f57 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -695,7 +695,8 @@ static PCIDeviceInfo virtio_info[] = {
             DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
             DEFINE_VIRTIO_NET_FEATURES(VirtIOPCIProxy, host_features),
             DEFINE_NIC_PROPERTIES(VirtIOPCIProxy, nic),
-            DEFINE_PROP_UINT32("txtimer", VirtIOPCIProxy, txtimer, 1),
+            DEFINE_PROP_UINT32("txtimer", VirtIOPCIProxy, txtimer,
+                               TXTIMER_DEFAULT),
             DEFINE_PROP_INT32("txburst", VirtIOPCIProxy, txburst, 256),
             DEFINE_PROP_END_OF_LIST(),
         },
diff --git a/hw/virtio.h b/hw/virtio.h
index 4051889..a1a17a2 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -183,6 +183,12 @@ void virtio_update_irq(VirtIODevice *vdev);
 void virtio_bind_device(VirtIODevice *vdev, const VirtIOBindings *binding,
                         void *opaque);
 
+#ifdef CONFIG_IOTHREAD
+ #define TXTIMER_DEFAULT 0
+#else
+ #define TXTIMER_DEFAULT 1
+#endif
+
 /* Base devices.  */
 VirtIODevice *virtio_blk_init(DeviceState *dev, BlockConf *conf);
 VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf,