netdev - Re: using software TSO on non-TSO capable netdevices

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Message-ID: <20080731101425.GE23814@xi.wantstofly.org>
Date:	Thu, 31 Jul 2008 12:14:25 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, akarkare@...vell.com,
	nico@....org
Subject: Re: using software TSO on non-TSO capable netdevices

On Thu, Jul 31, 2008 at 11:03:39AM +0800, Herbert Xu wrote:

> > The maximum that splice will allow -- PIPE_BUFFERS * PAGE_SIZE.
> > 
> > I.e. the writes should be large enough.
> 
> Have you looked at the packet dump? Maybe it was being constrained
> by the receiver/congestion windows.

The receiver seems to advertise a large enough window (700-ish KiB,
while the RTT is ~ 0.1 ms).  As to the congestion window, I had the
idea that it's not increasing beyond ~2-3 because the RTT is so low so
it doesn't need much data to fill the pipe, but I'm not a TCP expert.

I've put a tcpdump taken on the receiving end (192.168.42.10) here:

	http://www.wantstofly.org/~buytenh/dump.bz2

I'll be happy to try other things. :-)
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