From owner-cvs-all@FreeBSD.ORG  Sun Nov 16 11:52:03 2003
Return-Path: <owner-cvs-all@FreeBSD.ORG>
Delivered-To: cvs-all@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 57C2016A4CE; Sun, 16 Nov 2003 11:52:03 -0800 (PST)
Received: from mail.chesapeake.net (chesapeake.net [208.142.252.6])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id F01A543FD7; Sun, 16 Nov 2003 11:52:01 -0800 (PST)
	(envelope-from jroberson@chesapeake.net)
Received: from localhost (jroberson@localhost)
	by mail.chesapeake.net (8.11.6/8.11.6) with ESMTP id hAGJptC29063;
	Sun, 16 Nov 2003 14:51:55 -0500 (EST)
	(envelope-from jroberson@chesapeake.net)
Date: Sun, 16 Nov 2003 14:51:55 -0500 (EST)
From: Jeff Roberson <jroberson@chesapeake.net>
To: Luigi Rizzo <rizzo@icir.org>
In-Reply-To: <20031116045306.A66798@xorpc.icir.org>
Message-ID: <20031116145103.C10222-100000@mail.chesapeake.net>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
cc: Andre Oppermann <oppermann@pipeline.ch>
cc: src-committers@FreeBSD.org
cc: cvs-all@FreeBSD.org
cc: cvs-src@FreeBSD.org
Subject: Re: cvs commit: src/sys/netinet in_var.h ip_fastfwd.c ip_flow.c
 ip_flow.h ip_input.c ip_output.c src/sys/sys mbuf.h src/sys/conf files
 src/sys/net if_arcsubr.c if_ef.c if_ethersubr.c if_fddisubr.c if_
X-BeenThere: cvs-all@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: CVS commit messages for the entire tree <cvs-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-all>,
	<mailto:cvs-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/cvs-all>
List-Post: <mailto:cvs-all@freebsd.org>
List-Help: <mailto:cvs-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-all>,
	<mailto:cvs-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 16 Nov 2003 19:52:03 -0000


On Sun, 16 Nov 2003, Luigi Rizzo wrote:

> On Sun, Nov 16, 2003 at 07:19:53AM -0500, Jeff Roberson wrote:
> ...
> > > might result in the second timing call being executed before
> > > the section of code in the middle is complete. There is
> > > some nonintuitive instruction (which i now forget) to flush the
> > > execution pipeline which can be used around the section of
> > > code you want to time.
> >
> > Reading the tsc is also a serializing instruction.  I often use it to
> > accurately measure things that take as few as 20 cycles
>
> no, according to the intel documentation it is not, and i
> myself have seen bogus results which clearly indicate that it
> is not. There was a thread on the freebsd mailing lists a few
> months ago.
>

I double checked, you're right.  It probably works out for me because
clobbering two registers is enough of a hazard to prevent too much
serialization.

Cheers,
Jeff


> 	cheers
> 	luigi
>