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[Qemu-devel] [PATCH] virtio-net: enable ioeventfd even if vhost=off
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH] virtio-net: enable ioeventfd even if vhost=off |
Date: |
Wed, 11 Jan 2017 09:38:15 +0100 |
virtio-net-pci does not enable ioeventfd for historical reasons (and
nobody ever checked whether it should be revisited). Note that other
backends do enable ioeventfd for virtio-net.
However, it has a major effect on performance. On Windows, throughput is
_multiplied_ by 2 or 3 on TCP_STREAM (on small packets it is "only" a 30%
improvement) and a little less so on TCP_MAERTS albeit still very much
statistically significant. Latency also has a single digit improvement.
This is not visible when using vhost, which forces ioeventfd=on, but it
is substantial without vhost. In addition, also on Windows and with the
RHEL 7.3 kernel, APICv seems to slow down virtio-net performance a bit,
but the penalty with this patch goes from -25% to -7%.
Signed-off-by: Paolo Bonzini <address@hidden>
---
hw/virtio/virtio-pci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 023a020..0cd42ae 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -2278,7 +2278,7 @@ static const TypeInfo virtio_serial_pci_info = {
static Property virtio_net_properties[] = {
DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
- VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, false),
+ VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
DEFINE_PROP_END_OF_LIST(),
};
--
2.9.3
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