linux-kernel - Re: [PATCH] sctp: Restore 'resent' bit to avoid retransmitted chunks for RTT measurements

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Date:	Mon, 25 Nov 2013 09:37:00 +0800
From:	Xufeng Zhang <xufeng.zhang@...driver.com>
To:	Vlad Yasevich <vyasevich@...il.com>
CC:	<nhorman@...driver.com>, <davem@...emloft.net>,
	<linux-sctp@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sctp: Restore 'resent' bit to avoid retransmitted chunks
 for RTT measurements

On 11/22/2013 10:18 PM, Vlad Yasevich wrote:
> On 11/22/2013 03:30 AM, Xufeng Zhang wrote:
>    
>> From: Signed-off-by: Xufeng Zhang<xufeng.zhang@...driver.com>
>>
>> Currently retransmitted DATA chunks could also be used for
>> RTT measurements since there are no flag to identify whether
>> the transmitted DATA chunk is a new one or a retransmitted one.
>> This problem is introduced by commit ae19c5486 ("sctp: remove
>> 'resent' bit from the chunk") which inappropriately removed the
>> 'resent' bit completely, instead of doing this, we should set
>> the resent bit only for the retransmitted DATA chunks.
>>
>> Signed-off-by: Xufeng Zhang<xufeng.zhang@...driver.com>
>> ---
>>   include/net/sctp/structs.h |    1 +
>>   net/sctp/output.c          |   23 +++++++++++++----------
>>   net/sctp/outqueue.c        |    3 +++
>>   net/sctp/sm_make_chunk.c   |    1 +
>>   4 files changed, 18 insertions(+), 10 deletions(-)
>>
>> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
>> index 2174d8d..ea0ca5f 100644
>> --- a/include/net/sctp/structs.h
>> +++ b/include/net/sctp/structs.h
>> @@ -629,6 +629,7 @@ 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 e650978..32c214d 100644
>> --- a/net/sctp/output.c
>> +++ b/net/sctp/output.c
>> @@ -467,17 +467,20 @@ int sctp_packet_transmit(struct sctp_packet *packet)
>>   	list_for_each_entry_safe(chunk, tmp,&packet->chunk_list, list) {
>>   		list_del_init(&chunk->list);
>>   		if (sctp_chunk_is_data(chunk)) {
>> -			/* 6.3.1 C4) When data is in flight and when allowed
>> -			 * by rule C5, a new RTT measurement MUST be made each
>> -			 * round trip.  Furthermore, new RTT measurements
>> -			 * SHOULD be made no more than once per round-trip
>> -			 * for a given destination transport address.
>> -			 */
>> -
>> -			if (!tp->rto_pending) {
>> -				chunk->rtt_in_progress = 1;
>> -				tp->rto_pending = 1;
>> +			if (!chunk->resent) {
>> +				/* 6.3.1 C4) When data is in flight and when allowed
>> +				 * by rule C5, a new RTT measurement MUST be made each
>> +				 * round trip.  Furthermore, new RTT measurements
>> +				 * SHOULD be made no more than once per round-trip
>> +				 * for a given destination transport address.
>> +				 */
>> +
>> +				if (!tp->rto_pending) {
>>      
> Could be combined as
>      if (!chunk->resent&&  !tp->rto_pending) {
>    

Got it!

>    
>> +					chunk->rtt_in_progress = 1;
>> +					tp->rto_pending = 1;
>> +				}
>>   			}
>> +
>>   			has_data = 1;
>>   		}
>>
>> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
>> index 94df758..70f4f56 100644
>> --- a/net/sctp/outqueue.c
>> +++ b/net/sctp/outqueue.c
>> @@ -446,6 +446,8 @@ 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.
>>   			 */
>> @@ -1375,6 +1377,7 @@ static void sctp_check_transmitted(struct sctp_outq *q,
>>   				 * instance).
>>   				 */
>>   				if (!tchunk->tsn_gap_acked&&
>> +				    !tchunk->resent&&
>>   				tchunk->rtt_in_progress) {
>>   					tchunk->rtt_in_progress = 0;
>>   					rtt = jiffies - tchunk->sent_at;
>> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
>> index fe69032..8fe89f8 100644
>> --- a/net/sctp/sm_make_chunk.c
>> +++ b/net/sctp/sm_make_chunk.c
>> @@ -1321,6 +1321,7 @@ struct sctp_chunk *sctp_chunkify(struct sk_buff *skb,
>>   	INIT_LIST_HEAD(&retval->list);
>>   	retval->skb		= skb;
>>   	retval->asoc		= (struct sctp_association *)asoc;
>> +	retval->resent          = 0;
>>      
> Not needed due to zeroed out malloc.
>    

Thank you!
Will send V2 later.



Thanks,
Xufeng

> -vlad
>
>    
>>   	retval->singleton	= 1;
>>
>>   	retval->fast_retransmit = SCTP_CAN_FRTX;
>>
>>      
>
>    

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