Re: [Lksctp-developers] Error in RTTVAR calculation

[Vlad Y. <vla...@hp...>]

Hi Christian

On 10/05/2010 12:25 AM, Christian Schoch wrote:
> Hi Jon,
>
> The problem is inside the calculation of RTTVAR, which could last in
> very high values for RTO. This wrong result exists when RTT is rising
> and is bigger than SRTT (the subtraction goes negative). With this
> patch is should be possible to set RTOmin = 1 and the RTO has its
> minimum of 4 times the clock granularity - if the connection is fast
> enough like a LAN connection.
>
> This patch should eliminate your problem.
>

I asked John (by mistake) to do the final patch.  Since you are the original
author, can you do a full submission with your sign-off?

Thanks
-vlad

> Schoch Christian
>
> -----------------------------------------------------------------------
>
> --- a/net/sctp/transport.c	2010-10-05 06:04:17.000000000 +0200
> +++ b/net/sctp/transport.c	2010-10-05 06:09:09.000000000 +0200
> @@ -334,7 +334,7 @@
> 		 * 1/8, rto_alpha would be expressed as 3.
> 		 */
> 		tp->rttvar = tp->rttvar - (tp->rttvar>>  sctp_rto_beta)
> -			+ ((abs(tp->srtt - rtt))>>  sctp_rto_beta);
> +			+ (((__u32)abs((long)tp->srtt - (long)rtt))>>  sctp_rto_beta);
> 		tp->srtt = tp->srtt - (tp->srtt>>  sctp_rto_alpha)
> 			+ (rtt>>  sctp_rto_alpha);
> 	} else {
>
> ---------------------------------------------
>
>
>
>> On 10/04/2010 04:04 PM, Jon Leighton wrote:
>>> Has there been any resolution to this issue?  Last July I reported a
>>> problem I'd observed with timeout intervals jumping from 1 second to 60
>>> seconds, and which I presume is related to this problem.  I saw the same
>>> results in both the 2.6.31 and 2.6.34 kernels.  I'm currently using
>>> 2.6.31 and finding that file transfers over a lossy connection simply
>>> halt because the server won't retransmit lost packets - at least not
>>> within 2 hours.  What is the maximum possible timeout value?  If the
>>> client closes the socket, I see the server start retransmitting the lost
>>> packets.  On 2.6.34 I haven't observed timeouts longer than 2 minutes,
>>> but occasionally the system crashes.
>>>
>>> If there's been any resolution, such as a newer kernel or even just a
>>> patch I can apply to my current kernel, I'd appreciate someone posting
>>> that info.  Thanks very much.
>>>
>>
>> Hi Jon
>>
>> I dropped the ball on this on.  I agree with your analysis and the proposed
>> correction.  Would you be willing to submit a formal patch for this with
>> a full write-up in the description.
>>
>> Thanks
>> -vlad
>>
>>
>>
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>
>
>
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