Re: Try to Implement load balancer for transmit & retransmit

[Vlad Yasevich <vyasevich@gmail.com>]

On 12/12/2013 03:42 PM, Chang Xiangzhong wrote:
> The current implementation uses only one path as the "active path" and one
> path as a "retran path". This patch tries to use all of the pathes for
> transmission. But I'm afraid there must be something missing, such things like
> state update and etcs. 
> 
> The current implementation is very simple - just distribute the load on all of
> the pathes - just check if it satisifes cwnd>flight_size.
> 

If you are interested in pursuing this work I recommend you look at
https://tools.ietf.org/id/draft-tuexen-tsvwg-sctp-multipath-06.txt

-vlad

> And comments would be appreciated! 
> ---
>  include/net/sctp/cmt.h   |    5 +++-
>  net/sctp/Makefile        |    4 +--
>  net/sctp/associola.c     |   33 +++++++++++++++++++--
>  net/sctp/cmt_debug.c     |    2 +-
>  net/sctp/outqueue.c      |   73 +++++++++++++++++++++++++++++++++++-----------
>  net/sctp/protocol.c      |    1 +
>  net/sctp/sm_sideeffect.c |    2 +-
>  7 files changed, 95 insertions(+), 25 deletions(-)
> 
> diff --git a/include/net/sctp/cmt.h b/include/net/sctp/cmt.h
> index edbbfc2..858def8 100644
> --- a/include/net/sctp/cmt.h
> +++ b/include/net/sctp/cmt.h
> @@ -47,8 +47,11 @@
>  	extern char* cmt_print_assoc(struct sctp_association *asoc);
>  	extern char* cmt_print_sackhdr(struct sctp_sackhdr *sack);
>  	extern char* cmt_print_queued_tsn(struct list_head *queue, 
> -					  struct sctp_transport *transport);
> +					  struct sctp_transport *t);
>  	extern char* cmt_print_cwnd(struct list_head *transport_list);
> +	
> +	extern struct sctp_transport* sctp_assoc_most_vacant_path(
> +			struct sctp_association *asoc);
>  #endif
>  
>  /* SACK Chunk Specific Flags*/
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 626bdca..28f1f60 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1295,6 +1295,33 @@ void sctp_assoc_update(struct sctp_association *asoc,
>  	sctp_auth_asoc_init_active_key(asoc, GFP_ATOMIC);
>  }
>  
> +struct sctp_transport*
> +sctp_assoc_most_vacant_path(struct sctp_association *asoc, int threshold)
> +{
> +	struct sctp_transport *t, *ret = NULL;
> +	int vacancy, best=-1;
> +	if (threshold < 0)
> +		threshold = 0;
> +	list_for_each_entry(t, &asoc->peer.transport_addr_list, transports) {
> +		vacancy = t->cwnd - t->flight_size;
> +		if (t->state != SCTP_ACTIVE || vacancy <= threshold /*t->pathmtu/4*/)
> +			continue;
> +		// This is in slow-start state
> +		if (t->ssthresh > t->cwnd) {
> +			ret = t;
> +			break;
> +		}
> +		if (vacancy > best) {
> +			best = vacancy;
> +			ret = t;	
> +		}
> +
> +
> +	}
> +	cmt_debug("==>Find a most vacant path: %p\n", ret);
> +	return ret;
> +}
> +
> 
> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
> index d20816d..9010080 100644
> --- a/net/sctp/outqueue.c
> +++ b/net/sctp/outqueue.c
> @@ -57,13 +57,13 @@
>  
>  #include <net/sctp/sctp.h>
>  #include <net/sctp/sm.h>
> -#include <net/sctp/cmt_debug.h>
> +#include <net/sctp/cmt.h>
>  
>  
>  /* Declare internal functions here.  */
> @@ -920,14 +920,32 @@ static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout)
>  		 * current cwnd).
>  		 */
>  		if (!list_empty(&q->retransmit)) {
> -			if (asoc->peer.retran_path->state = SCTP_UNCONFIRMED)
> -				goto sctp_flush_out;
> -			if (transport = asoc->peer.retran_path)
> -				goto retran;
>  
> -			/* Switch transports & prepare the packet.  */
> -
> -			transport = asoc->peer.retran_path;
> +if (q->fast_rtx && !rtx_timeout)
> +{
> +	struct sctp_chunk *chunk, *chunk1;
> +	int chunk_size = 0; // not count the header!
> +	list_for_each_entry_safe(
> +			chunk, chunk1, &q->retransmit, transmitted_list) {
> +		// not the one to fast_rtx
> +		if (sctp_chunk_abandoned(chunk) 
> +		    || chunk->tsn_gap_acked
> +		    || !chunk->fast_retransmit) {
> +			continue;
> +		}
> +		// found the chunk to fast_rtx
> +		chunk_size = ntohs(chunk->chunk_hdr->length);
> +		break;	
> +	}
> +	transport = sctp_assoc_most_vacant_path(asoc, chunk_size);
> +	cmt_debug("%s: fast_rtx most vacant=%p, chunk_size=%d", __func__, transport, chunk_size);
> +} else {
> +	transport = sctp_assoc_most_vacant_path(asoc, -1);
> +}
> +			if (!transport) {
> +				cmt_debug("could not find a vacant path!\n");
> +				goto sctp_flush_out;
> +			}
>  
>  			if (list_empty(&transport->send_ready)) {
>  				list_add_tail(&transport->send_ready,
> @@ -989,12 +1007,22 @@ static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout)
>  			/* If there is a specified transport, use it.
>  			 * Otherwise, we want to use the active path.
>  			 */
> -			new_transport = chunk->transport;
> +			bool path_specified;
> +retry:			new_transport = chunk->transport;
>  			if (!new_transport ||
>  			    ((new_transport->state = SCTP_INACTIVE) ||
>  			     (new_transport->state = SCTP_UNCONFIRMED) ||
> -			     (new_transport->state = SCTP_PF)))
> -				new_transport = asoc->peer.active_path;
> +			     (new_transport->state = SCTP_PF))) {
> +				path_specified = false;
> +				// new_transport = asoc->peer.active_path;
> +				new_transport = sctp_assoc_most_vacant_path(
> +						asoc, -1);
> +				if (!new_transport) {// no available path
> +					sctp_outq_head_data(q, chunk);
> +					goto sctp_flush_out;
> +				}
> +			} else 
> +				path_specified = true;
>  			if (new_transport->state = SCTP_UNCONFIRMED)
>  				continue;
>  
> @@ -1032,7 +1060,18 @@ static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout)
>  
>  			switch (status) {
>  			case SCTP_XMIT_CWND_FULL:// 3
> -			case SCTP_XMIT_PMTU_FULL://1
> +				cmt_debug("==>CWND full\n");
> +				// The App didn't specify a path, so the path
> +				// was chosen by us. Then we could retry with
> +				// another path
> +				if (!path_specified) {
> +					cmt_debug("==>retry!\n");
> +					goto retry;
> +				}	       
> +			// PMTU_FULL not likely. As sctp_packet_transmit_chunk
> +			// would flush the transport and transmit the next 
> +			// chunk in the queue if PMTU_FULL happens.
> +			case SCTP_XMIT_PMTU_FULL://1 
>  			case SCTP_XMIT_RWND_FULL://2
>  			case SCTP_XMIT_NAGLE_DELAY://4
>  				/* We could not append this chunk, so put
>