linux-kernel - Re: Raise initial congestion window size / speedup slow start?

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Message-ID: <4C3E02D7.3080500@wildgooses.com>
Date:	Wed, 14 Jul 2010 19:32:55 +0100
From:	Ed W <lists@...dgooses.com>
To:	Bill Davidsen <davidsen@....com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Raise initial congestion window size / speedup slow start?


>> Does someone have some pointers on where to look to modify initial 
>> congestion window please?
>>
> Are you sure that's the issue? The backlog is in incoming, is it not?

Well, I was simplifying a little bit, actually I have a bunch of 
protocols in use, http is one of them


> Having dealt with moderately long delays push TB between timezones, 
> have you set your window size up? Set 
> /proc/sys/net/ipv4/tcp_adv_win_scale to 5 or 6 and see if that helps. 
> You may have to go into /proc/sys/net/core and crank up the rmem_* 
> settings, depending on your distribution.
>
> This allows the server to push a lot of data without an ack, which is 
> what you want, the ack will be delayed by the long latency, so this helps.

I think I'm misunderstanding something fundamental here:

- Surely the limited congestion window is what throttles me at 
connection initialisation time and this will not be affected by changing 
the params you mention above?  For sure the sliding window will be 
relevant vs my bandwidth delay product once the tcp connection reaches 
steady state, but I'm mostly worried here about performance right at the 
creation of the connection?

- Both you and Alan mention that the bulk of the traffic is "incoming" - 
this implies you think it's relevant?  Obviously I'm missing something 
fundamental here because my understanding is that the congestion window 
shuts us down in both directions (at the start of the connection?)

Thanks for the replies - I will take it over to netdev

Ed W
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