netdev - Re: TSO trimming question

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Message-Id: <20071221.013642.29817274.davem@davemloft.net>
Date:	Fri, 21 Dec 2007 01:36:42 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	billfink@...dspring.com, ilpo.jarvinen@...sinki.fi,
	netdev@...r.kernel.org, jheffner@....edu
Subject: Re: TSO trimming question

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Fri, 21 Dec 2007 17:29:27 +0800

> On Fri, Dec 21, 2007 at 01:27:20AM -0800, David Miller wrote:
> >
> > It's two shifts, and this gets scheduled along with the other
> > instructions on many cpus so it's effectively free.
> > 
> > I don't see why this is even worth mentioning and discussing.
> 
> I totally agree.  Two shifts are way better than a branch.

We take probably a thousand+ 100+ cycle cache misses in the TCP stack
on big window openning ACKs.

Instead of discussing ways to solve that huge performance killer we're
wanking about two friggin' integer shifts.

It's hilarious isn't it? :-)

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