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

[Jan Kiszka]

On 2012-05-31 12:03, Paolo Bonzini wrote:
> 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 */

Looks good.

Jan

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