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List:       linux-sctp
Subject:    Re: Strange slow transfer behavior on local host connection
From:       Jerry Jerry <jerry.jerry2008 () gmail ! com>
Date:       2015-03-16 23:35:38
Message-ID: CAAyB5cJcEf+eo3CvG_kpkzianLbBQGQGi3kYOdrtRpd-N7GjKQ () mail ! gmail ! com
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Thanks a lot, vlad, I'll give it a try.

Regards,
Jerry

On Mon, Mar 16, 2015 at 3:24 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> On 03/16/2015 12:37 PM, Jerry Jerry wrote:
>> Hello everyone,
>>
>> We have found a very strange behavior where the transfer is
>> particularly slower when sending data to a socket connecting ports on
>> the same host, but rather faster to the socket connecting ports on
>> different host.  /proc/net/sctp/assoc shows that TX_QUEUE of same host
>> socket buffers a lot of data but RX_QUEUE of the socket on the
>> receiving side is almost empty. On the contrary, both TX_QUEUE and
>> RX_QUEUE are almost empty for those sockets connecting different
>> hosts.
>>
>> We first thought this might because the processing difference between
>> local and remote hosts, but the problem remains the same even for a
>> symmetric case where both hosts send same messages to both its own
>> local and remote receiver, and receive messages via different local
>> and remote connections. In our opinion, the data transfer should be
>> faster or at least the same when sending to a socket connecting local
>> ports.
>>
>> This problem particularly occurs when the message size is small, but
>> playing with SCTP NODELAY option doesn't help.
>
> This is mostly likely due to the congestion window not being able to
> grow because the loopback mtu is higher then amount of queued data.
>
> You could try tweaking the loopback MTU to see if it changes things..
>
> -vlad
>
>>
>> I'm not sure if I may have missed anything, but any comments to shed
>> lights on this, or suggestions to tune would be appreciated very much!
>>
>> Regards,
>> Jerry
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