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

Paolo Bonzini
2012-05-23T16:00:30Z

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,