diff mbox

[PULL,04/11] virtio-pci: use zero length mmio eventfd for 1.0 notification cap when possible

Message ID 1447340097-18216-5-git-send-email-mst@redhat.com
State New
Headers show

Commit Message

Michael S. Tsirkin Nov. 12, 2015, 3:09 p.m. UTC 
From: Jason Wang <jasowang@redhat.com>

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 zero length 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 when
fast mmio is supported by host kernel.

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>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/virtio/virtio-pci.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)
diff mbox

Patch

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index ab2a372..9c3f6e3 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -270,6 +270,7 @@  static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
     EventNotifier *notifier = virtio_queue_get_host_notifier(vq);
     bool legacy = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_LEGACY);
     bool modern = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN);
+    bool fast_mmio = kvm_ioeventfd_any_length_enabled();
     MemoryRegion *modern_mr = &proxy->notify.mr;
     MemoryRegion *legacy_mr = &proxy->bar;
     hwaddr modern_addr = QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
@@ -286,8 +287,13 @@  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);
+            if (fast_mmio) {
+                memory_region_add_eventfd(modern_mr, modern_addr, 0,
+                                          false, n, notifier);
+            } else {
+                memory_region_add_eventfd(modern_mr, modern_addr, 2,
+                                          false, n, notifier);
+            }
         }
         if (legacy) {
             memory_region_add_eventfd(legacy_mr, legacy_addr, 2,
@@ -295,8 +301,13 @@  static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
         }
     } else {
         if (modern) {
-            memory_region_del_eventfd(modern_mr, modern_addr, 2,
-                                      true, n, notifier);
+            if (fast_mmio) {
+                memory_region_del_eventfd(modern_mr, modern_addr, 0,
+                                          false, n, notifier);
+            } else {
+                memory_region_del_eventfd(modern_mr, modern_addr, 2,
+                                          false, n, notifier);
+            }
         }
         if (legacy) {
             memory_region_del_eventfd(legacy_mr, legacy_addr, 2,