From owner-freebsd-current@FreeBSD.ORG  Mon Dec  6 17:58:28 2010
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 28F561065670;
	Mon,  6 Dec 2010 17:58:28 +0000 (UTC) (envelope-from avg@freebsd.org)
Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140])
	by mx1.freebsd.org (Postfix) with ESMTP id 40AFA8FC08;
	Mon,  6 Dec 2010 17:58:26 +0000 (UTC)
Received: from odyssey.starpoint.kiev.ua (alpha-e.starpoint.kiev.ua
	[212.40.38.101])
	by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id TAA13487;
	Mon, 06 Dec 2010 19:58:25 +0200 (EET) (envelope-from avg@freebsd.org)
Message-ID: <4CFD2441.5090408@freebsd.org>
Date: Mon, 06 Dec 2010 19:58:25 +0200
From: Andriy Gapon <avg@freebsd.org>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US;
	rv:1.9.2.12) Gecko/20101029 Lightning/1.0b2 Thunderbird/3.1.6
MIME-Version: 1.0
To: Jung-uk Kim <jkim@freebsd.org>
References: <4CF92852.20705@freebsd.org> <201012031938.12684.jkim@FreeBSD.org>
	<4CFA220A.30405@freebsd.org> <201012061243.08577.jkim@FreeBSD.org>
In-Reply-To: <201012061243.08577.jkim@FreeBSD.org>
X-Enigmail-Version: 1.1.2
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Cc: freebsd-current@freebsd.org
Subject: Re: non-invariant tsc and cputicker
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 06 Dec 2010 17:58:28 -0000

on 06/12/2010 19:42 Jung-uk Kim said the following:
> Sigh...  Please see the history of calcru() in 
> sys/kern/kern_resource.c.  Most important ones are:
> 
> http://svn.freebsd.org/viewvc/base?view=revision&revision=155444
> http://svn.freebsd.org/viewvc/base?view=revision&revision=155534
> 
> Basically, we chose efficiency over accuracy and you are suggesting 
> going backwards.

Well, I guess that it depends.

Looking at r155444 - the time is still going to be accounted in ticks (but
timecounter ticks).  BTW, I think that this quote says something: "On more modern
hardware no change in performance is seen." and that was ~5 years ago.

Looking at r155534 - the only change that is going to get undone is using TSC for
the accounting ticks, and that is only for machines with non-invariant TSC.  And I
think that all sufficiently modern machines have invariant TSC and, in Intel's
words, that's an architectural path going forward.

So, I don't think that I propose a dramatic change.
-- 
Andriy Gapon