Re: [Qemu-devel] [PATCH 4/6] virtio-pci: use wildcard mmio eventfd for 1.0 notification cap

[Jason Wang <jasowang@redhat.com>]

On 08/25/2015 12:30 AM, Greg Kurz wrote:
> On Fri, 21 Aug 2015 17:05:48 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>> > We use data match eventfd for 1.0 notification currently. This could
>> > be slow since software decoding is needed for mmio exit. To speed this
>> > up, we can switch to use wild card mmio eventfd for 1.0 notification
>> > since we can examine the queue index directly from the writing
>> > address. KVM kernel module can utilize this by registering it to fast
>> > mmio bus which could be as fast as pio on ept capable machine.
>> > 
>> > Lots of improvements were seen on a ept capable machine:
>> > 
>> > Guest RX:(TCP)
>> > size/session/+throughput%/+cpu%/-+per cpu%/
>> > 64/1/+1.6807%/[-16.2421%]/[+21.3984%]/
>> > 64/2/+0.6091%/[-11.0187%]/[+13.0678%]/
>> > 64/4/+0.0553%/[-5.9768%]/[+6.4155%]/
>> > 64/8/+0.1206%/[-4.0057%]/[+4.2984%]/
>> > 256/1/-0.0031%/[-10.1166%]/[+11.2517%]/
>> > 256/2/-0.5058%/[-6.1656%]/+6.0317%]/
>> > ...
>> > 
>> > Guest TX:(TCP)
>> > size/session/+throughput%/+cpu%/-+per cpu%/
>> > 64/1/[+18.9183%]/-0.2823%/[+19.2550%]/
>> > 64/2/[+13.5714%]/[+2.2675%]/[+11.0533%]/
>> > 64/4/[+13.1070%]/[+2.1817%]/[+10.6920%]/
>> > 64/8/[+13.0426%]/[+2.0887%]/[+10.7299%]/
>> > 256/1/[+36.2761%]/+6.3434%/[+28.1471%]/
>> > ...
>> > 1024/1/[+44.8873%]/+2.0811%/[+41.9335%]/
>> > ...
>> > 1024/4/+0.0228%/[-2.2044%]/[+2.2774%]/
>> > ...
>> > 16384/2/+0.0127%/[-5.0346%]/[+5.3148%]/
>> > ...
>> > 65535/1/[+0.0062%]/[-4.1183%]/[+4.3017%]/
>> > 65535/2/+0.0004%/[-4.2311%]/[+4.4185%]/
>> > 65535/4/+0.0107%/[-4.6106%]/[+4.8446%]/
>> > 65535/8/-0.0090%/[-5.5178%]/[+5.8306%]/
>> > 
>> > Latency:(TCP_RR)
>> > size/session/+transaction rate%/+cpu%/-+per cpu%/
>> > 64/1/[+6.5248%]/[-9.2882%]/[+17.4322%]/
>> > 64/25/[+11.0854%]/[+0.8000%]/[+10.2038%]/
>> > 64/50/[+12.1076%]/[+2.4627%]/[+9.4131%]/
>> > 256/1/[+5.3677%]/[+10.5669%]/-4.7024%/
>> > 256/25/[+5.6402%]/-0.8962%/[+6.5955%]/
>> > 256/50/[+5.9685%]/[+1.7766%]/[+4.1188%]/
>> > 4096/1/+0.2508%/[-10.4941%]/[+12.0047%]/
>> > 4096/25/[+1.8533%]/-0.0273%/+1.8812%/
>> > 4096/50/[+1.2156%]/-1.4134%/+2.6667%/
>> > 
>> > Notes: data with '[]' is the one whose significance is greater than 95%.
>> > 
>> > Thanks Wenli Quan <wquan@redhat.com> for the benchmarking.
>> > 
>> > Cc: Michael S. Tsirkin <mst@redhat.com>
>> > Signed-off-by: Jason Wang <jasowang@redhat.com>
>> > ---
>> >  hw/virtio/virtio-pci.c | 8 ++++----
>> >  1 file changed, 4 insertions(+), 4 deletions(-)
>> > 
>> > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>> > index d785623..fbd1f1f 100644
>> > --- a/hw/virtio/virtio-pci.c
>> > +++ b/hw/virtio/virtio-pci.c
>> > @@ -226,8 +226,8 @@ static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
>> >          }
>> >          virtio_queue_set_host_notifier_fd_handler(vq, true, set_handler);
>> >          if (modern) {
>> > -            memory_region_add_eventfd(modern_mr, modern_addr, 2,
>> > -                                      true, n, notifier);
>> > +            memory_region_add_eventfd(modern_mr, modern_addr, 0,
>> > +                                      false, n, notifier);
> This calls for the following change in memory.c:
>
>  static void adjust_endianness(MemoryRegion *mr, uint64_t *data, unsigned size)
>  {
> -    if (memory_region_wrong_endianness(mr)) {
> +    if (size && memory_region_wrong_endianness(mr)) {
>
>
> otherwise we abort on PPC64.
>

Right, will fix this in V2.

Thanks