From owner-freebsd-hackers@FreeBSD.ORG Wed Jun 1 05:40:37 2011 Return-Path: Delivered-To: freebsd-hackers@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 96403106564A; Wed, 1 Jun 2011 05:40:37 +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 B4E8F8FC0C; Wed, 1 Jun 2011 05:40:36 +0000 (UTC) Received: from porto.starpoint.kiev.ua (porto-e.starpoint.kiev.ua [212.40.38.100]) by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id IAA26536; Wed, 01 Jun 2011 08:40:34 +0300 (EEST) (envelope-from avg@FreeBSD.org) Received: from localhost ([127.0.0.1]) by porto.starpoint.kiev.ua with esmtp (Exim 4.34 (FreeBSD)) id 1QReAU-000KAf-H2; Wed, 01 Jun 2011 08:40:34 +0300 Message-ID: <4DE5D0D1.1030903@FreeBSD.org> Date: Wed, 01 Jun 2011 08:40:33 +0300 From: Andriy Gapon User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US; rv:1.9.2.17) Gecko/20110503 Lightning/1.0b2 Thunderbird/3.1.10 MIME-Version: 1.0 To: Jung-uk Kim References: <201105241356.45543.jkim@FreeBSD.org> <4DE4CE82.4030301@FreeBSD.org> <201105311616.31256.jkim@FreeBSD.org> In-Reply-To: <201105311616.31256.jkim@FreeBSD.org> X-Enigmail-Version: 1.1.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: freebsd-hackers@FreeBSD.org Subject: Re: [RFC] Enabling invariant TSC timecounter on SMP X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 01 Jun 2011 05:40:37 -0000 on 31/05/2011 23:16 Jung-uk Kim said the following: > On Tuesday 31 May 2011 07:18 am, Andriy Gapon wrote: >> on 24/05/2011 20:56 Jung-uk Kim said the following: >>> I think it's about time to enable invariant TSC timecounter on >>> SMP by default. Please see the attached patch. It is also >>> available from here: >>> >>> http://people.freebsd.org/~jkim/tsc_smp_test4.diff >>> >>> avg convinced me enough that it should be an opt-out feature >>> going forward. :-) >> >> Not sure if I really did that. >> My position is this: >> - if we think that TSC is SMP-safe then it should have the best >> priority >> - we should do our best to auto-guess if TSC is SMP-safe >> unless a user explicitly overrides that property (either via >> explicit testing or by making guesses based on CPU model or etc) > > I am sorry if I misunderstood your intention. However, I added > explicit boot-time TSC sanity check (to do our best to auto-guess) > and I think TSC is fairly SMP-safe. Hence, I thought that it is > about time for the change. In this case - yes. But I remember that you were thinking about either improving or simplifying that check or both. >>> Comments? >> >> Perhaps I missed it, but I don't remember the "lowres" part of the >> patch being discussed. > > No, it wasn't discussed with you. Do you see any problem with that > code? I don't see any obvious problem, but I also don't understand rationale of using smaller max_freq for the ncpus > 1 case. Maybe these two logical changes should be done as two separate commits. -- Andriy Gapon