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

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Aug 27, 2010 at 04:37:45PM -0600, Alex Williamson wrote:
> 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>

parameter having different settings based on config
options might surprise some users. I don't think
we really need a parameter here ...

> ---
> 
>  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
> +

Add a comment explaning that this is just a performance optimization?

>  /* Base devices.  */
>  VirtIODevice *virtio_blk_init(DeviceState *dev, BlockConf *conf);
>  VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf,
> 
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