On 07/09/2014 04:29 AM, David Laight wrote:
> The check for Nagle contains 6 separate checks all of which must be true
> before a data packet is delayed.
> Separate out each into its own 'if (test) return SCTP_XMIT_OK' so that
> the reasons can be individually described.
>
> Also return directly with SCTP_XMIT_RWND_FULL.
> Delete the now-unused 'retval' variable and 'finish' label from
> sctp_packet_can_append_data().
>
> Signed-off-by: David Laight <david.laight@xxxxxxxxxx>
> ---
> net/sctp/output.c | 69 +++++++++++++++++++++++++++++--------------------------
> 1 file changed, 36 insertions(+), 33 deletions(-)
>
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index 0f4d15f..553ba1d 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -633,7 +633,6 @@ nomem:
> static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
> struct sctp_chunk *chunk)
> {
> - sctp_xmit_t retval = SCTP_XMIT_OK;
> size_t datasize, rwnd, inflight, flight_size;
> struct sctp_transport *transport = packet->transport;
> struct sctp_association *asoc = transport->asoc;
> @@ -658,15 +657,11 @@ static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
>
> datasize = sctp_data_size(chunk);
>
> - if (datasize > rwnd) {
> - if (inflight > 0) {
> - /* We have (at least) one data chunk in flight,
> - * so we can't fall back to rule 6.1 B).
> - */
> - retval = SCTP_XMIT_RWND_FULL;
> - goto finish;
> - }
> - }
> + if (datasize > rwnd && inflight > 0)
> + /* We have (at least) one data chunk in flight,
> + * so we can't fall back to rule 6.1 B).
> + */
> + return SCTP_XMIT_RWND_FULL;
>
> /* RFC 2960 6.1 Transmission of DATA Chunks
> *
> @@ -680,36 +675,44 @@ static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
> * When a Fast Retransmit is being performed the sender SHOULD
> * ignore the value of cwnd and SHOULD NOT delay retransmission.
> */
> - if (chunk->fast_retransmit != SCTP_NEED_FRTX)
> - if (flight_size >= transport->cwnd) {
> - retval = SCTP_XMIT_RWND_FULL;
> - goto finish;
> - }
> + if (chunk->fast_retransmit != SCTP_NEED_FRTX &&
> + flight_size >= transport->cwnd)
> + return SCTP_XMIT_RWND_FULL;
>
> /* Nagle's algorithm to solve small-packet problem:
> * Inhibit the sending of new chunks when new outgoing data arrives
> * if any previously transmitted data on the connection remains
> * unacknowledged.
> */
> - if (!sctp_sk(asoc->base.sk)->nodelay && sctp_packet_empty(packet) &&
> - inflight && sctp_state(asoc, ESTABLISHED)) {
> - unsigned int max = transport->pathmtu - packet->overhead;
> - unsigned int len = chunk->skb->len + q->out_qlen;
> -
> - /* Check whether this chunk and all the rest of pending
> - * data will fit or delay in hopes of bundling a full
> - * sized packet.
> - * Don't delay large message writes that may have been
> - * fragmeneted into small peices.
> - */
> - if ((len < max) && chunk->msg->can_delay) {
> - retval = SCTP_XMIT_NAGLE_DELAY;
> - goto finish;
> - }
> - }
>
> -finish:
> - return retval;
> + if (sctp_sk(asoc->base.sk)->nodelay)
> + /* Nagle disabled */
> + return SCTP_XMIT_OK;
> +
> + if (!sctp_packet_empty(packet))
> + /* Append to packet */
> + return SCTP_XMIT_OK;
> +
> + if (inflight != 0)
> + /* Nothing unacked */
> + return SCTP_XMIT_OK;
This doesn't look right. First, the comment doesn't match the condition.
Second, when we have stuff in-flight we might be affected be Nagle. Thus,
I think the condition should be:
if (!inflight)
Then the commend and logic holds.
-vlad
> +
> + if (!sctp_state(asoc, ESTABLISHED))
> + return SCTP_XMIT_OK;
> +
> + /* Check whether this chunk and all the rest of pending data will fit
> + * or delay in hopes of bundling a full sized packet.
> + */
> + if (chunk->skb->len + q->out_qlen >= transport->pathmtu - packet->overhead)
> + /* Enough data queued to fill a packet */
> + return SCTP_XMIT_OK;
> +
> + /* Don't delay large message writes that may have been fragmented */
> + if (!chunk->msg->can_delay)
> + return SCTP_XMIT_OK;
> +
> + /* Defer until all data acked or packet full */
> + return SCTP_XMIT_NAGLE_DELAY;
> }
>
> /* This private function does management things when adding DATA chunk */
>
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