netdev - Re: [PATCH net 2/5] sctp: reuse sent_count to avoid retransmitted chunks for RTT measurements

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Date:   Mon, 26 Sep 2016 09:13:01 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Vlad Yasevich <vyasevich@...il.com>, daniel@...earbox.net
Subject: Re: [PATCH net 2/5] sctp: reuse sent_count to avoid retransmitted
 chunks for RTT measurements

On Mon, Sep 26, 2016 at 05:47:51PM +0800, Xin Long wrote:
> Now sctp uses chunk->resent to record if a chunk is retransmitted, for
> RTT measurements with retransmitted DATA chunks. chunk->sent_count was
> introduced to record how many times one chunk has been sent for prsctp
> RTX policy before. We actually can know if one chunk is retransmitted
> by checking chunk->sent_count is greater than 1.
> 
> This patch is to remove resent from sctp_chunk and reuse sent_count
> to avoid retransmitted chunks for RTT measurements.
> 
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  include/net/sctp/structs.h | 1 -
>  net/sctp/output.c          | 3 ++-
>  net/sctp/outqueue.c        | 4 +---
>  3 files changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 4f097f5..81a5faa 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -647,7 +647,6 @@ struct sctp_chunk {
>  #define SCTP_NEED_FRTX 0x1
>  #define SCTP_DONT_FRTX 0x2
>  	__u16	rtt_in_progress:1,	/* This chunk used for RTT calc? */
> -		resent:1,		/* Has this chunk ever been resent. */
>  		has_tsn:1,		/* Does this chunk have a TSN yet? */
>  		has_ssn:1,		/* Does this chunk have a SSN yet? */
>  		singleton:1,		/* Only chunk in the packet? */
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index 31b7bc3..483d2ed 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -547,7 +547,8 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
>  				 * for a given destination transport address.
>  				 */
>  
> -				if (!chunk->resent && !tp->rto_pending) {
> +				if (chunk->sent_count == 1 &&
> +				    !tp->rto_pending) {
>  					chunk->rtt_in_progress = 1;
>  					tp->rto_pending = 1;
>  				}
> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
> index 72e54a4..2a629fa 100644
> --- a/net/sctp/outqueue.c
> +++ b/net/sctp/outqueue.c
> @@ -536,8 +536,6 @@ void sctp_retransmit_mark(struct sctp_outq *q,
>  				transport->rto_pending = 0;
>  			}
>  
> -			chunk->resent = 1;
> -
>  			/* Move the chunk to the retransmit queue. The chunks
>  			 * on the retransmit queue are always kept in order.
>  			 */
> @@ -1467,7 +1465,7 @@ static void sctp_check_transmitted(struct sctp_outq *q,
>  				 * instance).
>  				 */
>  				if (!tchunk->tsn_gap_acked &&
> -				    !tchunk->resent &&
> +				    tchunk->sent_count == 1 &&
>  				    tchunk->rtt_in_progress) {
>  					tchunk->rtt_in_progress = 0;
>  					rtt = jiffies - tchunk->sent_at;
> -- 
> 2.1.0
> 

Maybe wrap this in a macro?  i.e.:
#define chunk_retransmitted(chunk) (chunk->sent_count > 1)

For readability?


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