linux-kernel - Re: [PATCH] net: sctp: set chunk->tsn_gap

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Date:	Fri, 22 Nov 2013 20:24:00 +0100
From:	Chang <changxiangzhong@...il.com>
To:	Vlad Yasevich <vyasevich@...il.com>, nhorman@...driver.com,
	davem@...emloft.net
CC:	linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sctp: set chunk->tsn_gap_acked at the end of cycle


On 11/22/2013 03:27 PM, Vlad Yasevich wrote:
> On 11/22/2013 02:49 AM, Chang Xiangzhong wrote:
>> tsn_gap_acked is an important state flag in chunk, which indicates if the
>> chunk has been acked in gap reports before.
> Actually, this bit indicates simply that the chunk has been acked.  It
> doesn't state whether it's been acked in a gap report or via cumulative tsn.
Thanks for pointing this out. Sorry for not having made that clear.
>
>> SFR-CACC algorithm depends on this
>> variable. So set this at the end of each iteration, otherwise the SFR-CACC
>> algorithm would never be toggled.
>>
>> Signed-off-by: Chang Xiangzhong <changxiangzhong@...il.com>
>> ---
>>   net/sctp/outqueue.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
>> index 1b494fa..bff828c 100644
>> --- a/net/sctp/outqueue.c
>> +++ b/net/sctp/outqueue.c
>> @@ -1396,7 +1396,6 @@ static void sctp_check_transmitted(struct sctp_outq *q,
>>   			 * while DATA was outstanding).
>>   			 */
>>   			if (!tchunk->tsn_gap_acked) {
>> -				tchunk->tsn_gap_acked = 1;
>>   				if (TSN_lt(*highest_new_tsn_in_sack, tsn))
>>   					*highest_new_tsn_in_sack = tsn;
>>   				bytes_acked += sctp_data_size(tchunk);
>> @@ -1460,6 +1459,8 @@ static void sctp_check_transmitted(struct sctp_outq *q,
>>   				 */
>>   				list_add_tail(lchunk, &tlist);
>>   			}
>> +
>> +			tchunk->tsn_gap_acked = 1;
> The current code will set the state if it hasn't been set yet.  Why is
> this needed?
Because in line 1420 ~ 1440 The SFR-CACC algorithms use tsn_gap_acked. 
That "if block" would never be triggered because the varaiable's been 
set. That's why I move the "state changing sentence" to the end of the 
iteration.
> Now there is an issue with tracking highest_new_tsn_in_sack.  The spec
> is a little vague on this, but the highest_new_tsn_in_sack only supposed
> to track tsns that have not been resent.  If a tsn has been reneged, and
> then sent again, it is not considered 'new' thus should not count
> toward highest_new_tsn_in_sack.  We currently do not track this right.
I'll try to figure this out.
> -vlad
>
> -vlad
>
>>   		} else {
>>   			if (tchunk->tsn_gap_acked) {
>>   				pr_debug("%s: receiver reneged on data TSN:0x%x\n",
>>

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