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

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Message-ID: <20080731093935.GB23814@xi.wantstofly.org>
Date:	Thu, 31 Jul 2008 11:39:35 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>,
	Netdev <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 09:55:57AM +0300, Ilpo Järvinen 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?
> 
> ...That would be helpful indeed.
> 
> > Maybe it was being constrained by the receiver/congestion windows.
> 
> The thing that came into my mind is that the link might still be fast 
> enough to make the transfer application limited, can you try setting 
> /proc/sys/net/ipv4/tcp_slow_start_after_idle to zero and retest.

>From a couple of quick tests, that doesn't seem to change anything
as far as transfer speed or CPU usage are concerned.
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