Re: [Qemu-devel] [PATCH v2 15/15] net: invoke qemu_can_send_packet only before net queue sending function

[Paolo Bonzini <pbonzini@redhat.com>]

Il 23/05/2012 17:14, zwu.kernel@gmail.com ha scritto:
> From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
> 
> Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
> ---
>  net/queue.c      |    4 ++--
>  net/slirp.c      |    7 -------
>  net/tap.c        |    2 +-
>  slirp/if.c       |    5 -----
>  slirp/libslirp.h |    1 -
>  5 files changed, 3 insertions(+), 16 deletions(-)
> 
> diff --git a/net/queue.c b/net/queue.c
> index 0afd783..d2e57de 100644
> --- a/net/queue.c
> +++ b/net/queue.c
> @@ -176,7 +176,7 @@ ssize_t qemu_net_queue_send(NetQueue *queue,
>  {
>      ssize_t ret;
>  
> -    if (queue->delivering) {
> +    if (queue->delivering || !qemu_can_send_packet(sender)) {
>          return qemu_net_queue_append(queue, sender, flags, data, size, NULL);
>      }
>  
> @@ -200,7 +200,7 @@ ssize_t qemu_net_queue_send_iov(NetQueue *queue,
>  {
>      ssize_t ret;
>  
> -    if (queue->delivering) {
> +    if (queue->delivering || !qemu_can_send_packet(sender)) {
>          return qemu_net_queue_append_iov(queue, sender, flags, iov, iovcnt, NULL);
>      }
>  
> diff --git a/net/slirp.c b/net/slirp.c
> index a6ede2b..248f7ff 100644
> --- a/net/slirp.c
> +++ b/net/slirp.c
> @@ -96,13 +96,6 @@ static void slirp_smb_cleanup(SlirpState *s);
>  static inline void slirp_smb_cleanup(SlirpState *s) { }
>  #endif
>  
> -int slirp_can_output(void *opaque)
> -{
> -    SlirpState *s = opaque;
> -
> -    return qemu_can_send_packet(&s->nc);
> -}
> -
>  void slirp_output(void *opaque, const uint8_t *pkt, int pkt_len)
>  {
>      SlirpState *s = opaque;
> diff --git a/net/tap.c b/net/tap.c
> index 65f45b8..7b1992b 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -210,7 +210,7 @@ static void tap_send(void *opaque)
>          if (size == 0) {
>              tap_read_poll(s, 0);
>          }
> -    } while (size > 0 && qemu_can_send_packet(&s->nc));
> +    } while (size > 0);

Can you explain this?  Also, have you benchmarked the change to see what
effect it has?

Also, can you explain why you didn't implement this?

>> If they did, hubs could then do their own flow control via can_receive.
>> When qemu_send_packet returns zero you increment a count of in-flight
>> packets, and a sent-packet callback would decrement the same count. When the
>> count is non-zero, can_receive returns false (and vice versa).  The sent_cb
>> also needs to call qemu_flush_queued_packets when the count drop to zero.
>> With this in place, I think the other TODO about the return value is easily
>> solved; receive/receive_iov callbacks can simply return immediate success,
>> and later block further sends.

Paolo

>  }
>  
>  int tap_has_ufo(NetClientState *nc)
> diff --git a/slirp/if.c b/slirp/if.c
> index 096cf6f..533295d 100644
> --- a/slirp/if.c
> +++ b/slirp/if.c
> @@ -177,11 +177,6 @@ void if_start(Slirp *slirp)
>      }
>  
>      while (ifm_next) {
> -        /* check if we can really output */
> -        if (!slirp_can_output(slirp->opaque)) {
> -            break;
> -        }
> -
>          ifm = ifm_next;
>          from_batchq = next_from_batchq;
>  
> diff --git a/slirp/libslirp.h b/slirp/libslirp.h
> index 77527ad..9b471b5 100644
> --- a/slirp/libslirp.h
> +++ b/slirp/libslirp.h
> @@ -25,7 +25,6 @@ void slirp_select_poll(fd_set *readfds, fd_set *writefds, fd_set *xfds,
>  void slirp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len);
>  
>  /* you must provide the following functions: */
> -int slirp_can_output(void *opaque);
>  void slirp_output(void *opaque, const uint8_t *pkt, int pkt_len);
>  
>  int slirp_add_hostfwd(Slirp *slirp, int is_udp,