From owner-cvs-src@FreeBSD.ORG Thu Oct 20 14:28:27 2005 Return-Path: X-Original-To: cvs-src@freebsd.org Delivered-To: cvs-src@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 472D616A420; Thu, 20 Oct 2005 14:28:27 +0000 (GMT) (envelope-from jhb@freebsd.org) Received: from mv.twc.weather.com (mv.twc.weather.com [65.212.71.225]) by mx1.FreeBSD.org (Postfix) with ESMTP id 39CE743D88; Thu, 20 Oct 2005 14:28:22 +0000 (GMT) (envelope-from jhb@freebsd.org) Received: from [10.50.41.234] (Not Verified[10.50.41.234]) by mv.twc.weather.com with NetIQ MailMarshal (v6, 0, 3, 8) id ; Thu, 20 Oct 2005 10:44:30 -0400 From: John Baldwin To: Bruce Evans Date: Thu, 20 Oct 2005 09:59:19 -0400 User-Agent: KMail/1.8.2 References: <200510172310.j9HNAVPL013057@repoman.freebsd.org> <200510181101.03956.jhb@freebsd.org> <20051020154709.U99720@delplex.bde.org> In-Reply-To: <20051020154709.U99720@delplex.bde.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200510200959.21234.jhb@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, Andrew Gallatin , cvs-all@freebsd.org, David Xu Subject: Re: cvs commit: src/sys/amd64/amd64 cpu_switch.S machdep.c X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 20 Oct 2005 14:28:27 -0000 On Thursday 20 October 2005 01:53 am, Bruce Evans wrote: > On Tue, 18 Oct 2005, John Baldwin wrote: > > On Tuesday 18 October 2005 09:44 am, Andrew Gallatin wrote: > >> It is a shame we can't find a way to use the TSC as a timecounter on > >> SMP systems. It seems that about 40% of the context switch time is > >> spent just waiting for the PIO read of the ACPI-fast or i8254 to > >> return. > > > > You can try it by just setting the kern.timecounter.smp_tsc=1 tunable on > > boot. > > There is no need for this. Just set the timecounter using sysctl after > booting (and quickly switch it back if it doesn't work). > > This tuneable, like most, shouldn't exist. It may be a relic from > when the TSC wasn't put in the list of available timecounters in the > SMP case. It is now put in the list with a negative "quaility", but > the sysctl to set the timecounter correctly not restricted by the > quality. Ah, I didn't realize the sysctl let you use negative quality timecounters. The tunable does serve to automate it for remote machines I guess since it doesn't pessimize the quality on SMP. -- John Baldwin <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org