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

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Message-ID: <4C3E0684.5060409@wildgooses.com>
Date:	Wed, 14 Jul 2010 19:48:36 +0100
From:	Ed W <lists@...dgooses.com>
To:	David Miller <davem@...emloft.net>
CC:	davidsen@....com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: Raise initial congestion window size / speedup slow start?

On 14/07/2010 19:15, David Miller wrote:
> From: Bill Davidsen<davidsen@....com>
> Date: Wed, 14 Jul 2010 11:21:15 -0400
>
>    
>> You may have to go into /proc/sys/net/core and crank up the
>> rmem_* settings, depending on your distribution.
>>      
> You should never, ever, have to touch the various networking sysctl
> values to get good performance in any normal setup.  If you do, it's a
> bug, report it so we can fix it.
>    

Just checking the basics here because I don't think this is a bug so 
much as a, less common installation that differs from the "normal" case.

- When we create a tcp connection we always start with tcp slow start
- This sets the congestion window to effectively 4 packets?
- This applies in both directions?
- Remote sender responds to my hypothetical http request with the first 
4 packets of data
- We need to wait one RTT for the ack to come back and now we can send 
the next 8 packets,
- Wait for the next ack and at 16 packets we are now moving at a 
sensible fraction of the bandwidth delay product?

So just to be clear:
- We don't seem to have any user-space tuning knobs to influence this 
right now?
- In this age of short attention spans, a couple of extra seconds 
between clicking something and it responding is worth optimising (IMHO)
- I think I need to take this to netdev, but anyone else with any ideas 
happy to hear them?

Thanks

Ed W
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