Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c

[Paolo Bonzini]

Il 31/05/2012 10:23, Jan Kiszka ha scritto:
>> > @@ -922,6 +923,7 @@ set_rdt(E1000State *s, int index, uint32_t val)
>> >  {
>> >      s->check_rxov = 0;
>> >      s->mac_reg[index] = val & 0xffff;
>> > +    qemu_notify_event();
> This still looks like the wrong tool: Packets that can't be delivered
> are queued.

Packets that are read from the tap but can't be delivered are queued;
packets that are left on the tap need qemu_notify_event to be flushed.

> So we need to flush the queue and clear the blocked delivery
> there. qemu_flush_queued_packets appears more appropriate for this.

Right, and qemu_flush_queued_packets needs to call qemu_notify_event
which makes the call in virtio-net unnecessary.

Paolo

diff --git a/hw/e1000.c b/hw/e1000.c
index 4573f13..43d933a 100644
--- a/hw/e1000.c
+++ b/hw/e1000.c
@@ -295,6 +295,7 @@ set_rx_control(E1000State *s, int index, uint32_t val)
     s->rxbuf_min_shift = ((val / E1000_RCTL_RDMTS_QUAT) & 3) + 1;
     DBGOUT(RX, "RCTL: %d, mac_reg[RCTL] = 0x%x\n", s->mac_reg[RDT],
            s->mac_reg[RCTL]);
+    qemu_flush_queued_packets(&s->nic->nc);
 }
 
 static void
@@ -926,6 +927,9 @@ set_rdt(E1000State *s, int index, uint32_t val)
 {
     s->check_rxov = 0;
     s->mac_reg[index] = val & 0xffff;
+    if (e1000_has_rxbufs(s, 1)) {
+        qemu_flush_queued_packets(&s->nic->nc);
+    }
 }
 
 static void
diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index 3f190d4..0974945 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -447,10 +447,6 @@ static void virtio_net_handle_rx(VirtIODevice *vdev, 
VirtQueue *vq)
     VirtIONet *n = to_virtio_net(vdev);
 
     qemu_flush_queued_packets(&n->nic->nc);
-
-    /* We now have RX buffers, signal to the IO thread to break out of the
-     * select to re-poll the tap file descriptor */
-    qemu_notify_event();
 }
 
 static int virtio_net_can_receive(VLANClientState *nc)
diff --git a/net.c b/net.c
index 1922d8a..fa846ae 100644
--- a/net.c
+++ b/net.c
@@ -491,7 +491,12 @@ void qemu_flush_queued_packets(VLANClientState *vc)
         queue = vc->send_queue;
     }
 
-    qemu_net_queue_flush(queue);
+    if (qemu_net_queue_flush(queue)) {
+        /* We emptied the queue successfully, signal to the IO thread to repoll
+         * the file descriptor (for tap, for example).
+         */
+        qemu_notify_event();
+    }
 }
 
 static ssize_t qemu_send_packet_async_with_flags(VLANClientState *sender,
diff --git a/net/queue.c b/net/queue.c
index 1ab5247..fd1c7e6 100644
--- a/net/queue.c
+++ b/net/queue.c
@@ -232,7 +232,7 @@ void qemu_net_queue_purge(NetQueue *queue, VLANClientState 
*from)
     }
 }
 
-void qemu_net_queue_flush(NetQueue *queue)
+bool qemu_net_queue_flush(NetQueue *queue)
 {
     while (!QTAILQ_EMPTY(&queue->packets)) {
         NetPacket *packet;
@@ -248,7 +248,7 @@ void qemu_net_queue_flush(NetQueue *queue)
                                      packet->size);
         if (ret == 0) {
             QTAILQ_INSERT_HEAD(&queue->packets, packet, entry);
-            break;
+            return 0;
         }
 
         if (packet->sent_cb) {
@@ -257,4 +257,5 @@ void qemu_net_queue_flush(NetQueue *queue)
 
         g_free(packet);
     }
+    return 1;
 }
diff --git a/net/queue.h b/net/queue.h
index a31958e..4bf6d3c 100644
--- a/net/queue.h
+++ b/net/queue.h
@@ -66,6 +66,6 @@ ssize_t qemu_net_queue_send_iov(NetQueue *queue,
                                 NetPacketSent *sent_cb);
 
 void qemu_net_queue_purge(NetQueue *queue, VLANClientState *from);
-void qemu_net_queue_flush(NetQueue *queue);
+bool qemu_net_queue_flush(NetQueue *queue);
 
 #endif /* QEMU_NET_QUEUE_H */