From owner-freebsd-net@FreeBSD.ORG  Mon Jul  7 23:21:59 2008
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
Delivered-To: freebsd-net@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id E455C106567D
	for <freebsd-net@freebsd.org>; Mon,  7 Jul 2008 23:21:59 +0000 (UTC)
	(envelope-from julian@elischer.org)
Received: from outN.internet-mail-service.net (outn.internet-mail-service.net
	[216.240.47.237])
	by mx1.freebsd.org (Postfix) with ESMTP id C9A678FC0C
	for <freebsd-net@freebsd.org>; Mon,  7 Jul 2008 23:21:59 +0000 (UTC)
	(envelope-from julian@elischer.org)
Received: from idiom.com (mx0.idiom.com [216.240.32.160])
	by out.internet-mail-service.net (Postfix) with ESMTP id 640A5242F;
	Mon,  7 Jul 2008 16:22:18 -0700 (PDT)
Received: from julian-mac.elischer.org (localhost [127.0.0.1])
	by idiom.com (Postfix) with ESMTP id 548992D6016;
	Mon,  7 Jul 2008 16:21:59 -0700 (PDT)
Message-ID: <4872A516.4000306@elischer.org>
Date: Mon, 07 Jul 2008 16:21:58 -0700
From: Julian Elischer <julian@elischer.org>
User-Agent: Thunderbird 2.0.0.14 (Macintosh/20080421)
MIME-Version: 1.0
To: Artem Belevich <fbsdlist@src.cx>
References: <4867420D.7090406@gtcomm.net>
	<486FFF70.3090402@gtcomm.net>	<48701921.7090107@gtcomm.net>
	<4871E618.1080500@freebsd.org>	<20080708002228.G680@besplex.bde.org>
	<48724238.2020103@freebsd.org>	<20080708034304.R21502@delplex.bde.org>	<20080708045135.V1022@besplex.bde.org>	<ed91d4a80807071227q5d9ca283g59270a1ab92c80a9@mail.gmail.com>	<48727BA9.6020702@elischer.org>
	<ed91d4a80807071533r5a93d24cpd01b5ec0f3b2c835@mail.gmail.com>
In-Reply-To: <ed91d4a80807071533r5a93d24cpd01b5ec0f3b2c835@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Cc: FreeBSD Net <freebsd-net@freebsd.org>
Subject: Re: Freebsd IP Forwarding performance (question,
 and some info) [7-stable, current, em, smp]
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 07 Jul 2008 23:22:00 -0000

Artem Belevich wrote:
>>  Prefetching when you are waiting for the data isn't a help.
> 
> Agreed. Got to start prefetch around <put your memory latency here>ns
> before you actually need the data and move on doing other things that
> do not depend on the data you've just started prefetching.
> 
>>  what you need is a speculative prefetch where you an tell teh processor "We
>> will probably need the following address so start getting it while we go do
>> other stuff".
> 
> It does not have to be 'speculative' either. 

"*Will*" is just a very definite subset of 'speculation' :-)

> In this particular case
> we have very good idea that we *will* need some data from ethernet
> header and, probably, IP and TCP headers as well. We might as well tel
> the hardware to start pulling data in without stalling the CPU. Intel
> has instructions specifically for this purpose. I assume AMD has them
> too.
> 
> --Artem
> _______________________________________________
> freebsd-net@freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-net
> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"