netdev - Re: tcp bw in 2.6

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Date:	Tue, 2 Oct 2007 10:10:55 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	lm@...mover.com (Larry McVoy)
Cc:	Larry McVoy <lm@...mover.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	torvalds@...ux-foundation.org, davem@...emloft.net,
	wscott@...mover.com, netdev@...r.kernel.org
Subject: Re: tcp bw in 2.6

On Tue, 2 Oct 2007 09:49:52 -0700
lm@...mover.com (Larry McVoy) wrote:

> On Tue, Oct 02, 2007 at 09:47:26AM -0700, Stephen Hemminger wrote:
> > On Tue, 2 Oct 2007 09:25:34 -0700
> > lm@...mover.com (Larry McVoy) wrote:
> > 
> > > > If the server side is the source of the data, i.e, it's transfer is a 
> > > > write loop, then I get the bad behaviour.  
> > > > ...
> > > > So is this a bug or intentional?
> > > 
> > > For whatever it is worth, I believed that we used to get better performance
> > > from the same hardware.  My guess is that it changed somewhere between
> > > 2.6.15-1-k7 and 2.6.18-5-k7.
> > 
> > For the period from 2.6.15 to 2.6.18, the kernel by default enabled TCP
> > Appropriate Byte Counting. This caused bad performance on applications that
> > did small writes.
> 
> It's doing 1MB writes.
> 
> Is there a sockopt to turn that off?  Or /proc or something?

sysctl -w net.ipv4.tcp_abc=0

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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