virtio: Inject virtio-blk interrupt quickly

Current blk interrupt is injected into guest after device handle a
batch of requests. While this patch injects interrupt at the end of each
request. So guest block will get much more interrupts and could handle
request more quickly.

With this patch, the guest fio read test improves 13%, while fio write
doesn't get better.

BUG=none
TEST=run fio_read and fio_write in guest

Change-Id: Ib0bd23e624dfc5d940d6cc124468b898d8ba128e
Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.corp-partner.google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2008338
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>

1 files changed, 5 insertions, 8 deletions

diff --git a/devices/src/virtio/block.rs b/devices/src/virtio/block.rs
index 30cf4f7..65be6d5 100644
--- a/devices/src/virtio/block.rs
+++ b/devices/src/virtio/block.rs
@@ -298,13 +298,13 @@ impl Worker {
         queue_index: usize,
         flush_timer: &mut TimerFd,
         flush_timer_armed: &mut bool,
-    ) -> bool {
+    ) {
         let queue = &mut self.queues[queue_index];
 
         let disk_size = self.disk_size.lock();
 
-        let mut needs_interrupt = false;
         while let Some(avail_desc) = queue.pop(&self.mem) {
+            queue.set_notify(&self.mem, false);
             let desc_index = avail_desc.index;
 
             let len = match Worker::process_one_request(
@@ -325,10 +325,9 @@ impl Worker {
             };
 
             queue.add_used(&self.mem, desc_index, len as u32);
-            needs_interrupt = true;
+            self.interrupt.signal_used_queue(queue.vector);
+            queue.set_notify(&self.mem, true);
         }
-
-        needs_interrupt
     }
 
     fn resize(&mut self, new_size: u64) -> DiskControlResult {
@@ -419,9 +418,7 @@ impl Worker {
                             error!("failed reading queue EventFd: {}", e);
                             break 'poll;
                         }
-                        if self.process_queue(0, &mut flush_timer, &mut flush_timer_armed) {
-                            self.interrupt.signal_used_queue(self.queues[0].vector);
-                        }
+                        self.process_queue(0, &mut flush_timer, &mut flush_timer_armed);
                     }
                     Token::ControlRequest => {
                         let req = match self.control_socket.recv() {