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

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Message-ID: <AANLkTil3MVGwJUG12dikut9X1s9Ozc_3GwMjx_gErvxI@mail.gmail.com>
Date:	Wed, 14 Jul 2010 21:51:51 -0700
From:	"H.K. Jerry Chu" <hkjerry.chu@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	davidsen@....com, lists@...dgooses.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Raise initial congestion window size / speedup slow start?

On Wed, Jul 14, 2010 at 11:15 AM, David Miller <davem@...emloft.net> 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.

Agreed, except there are indeed bugs in the code today in that the
code in various places assumes initcwnd as per RFC3390. So when
initcwnd is raised, that actual value may be limited unnecessarily by
the initial wmem/sk_sndbuf.

Will try to find time to submit a patch.

Jerry

>
> I cringe every time someone says to do this, so please do me a favor
> and don't spread this further. :-)
>
> For one thing, TCP dynamically adjusts the socket buffer sizes based
> upon the behavior of traffic on the connection.
>
> And the TCP memory limit sysctls (not the core socket ones) are sized
> based upon available memory.  They are there to protect you from
> situations such as having so much memory dedicated to socket buffers
> that there is none left to do other things effectively.  It's a
> protective limit, rather than a setting meant to increase or improve
> performance.  So like the others, leave these alone too.
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