From owner-cvs-src@FreeBSD.ORG Thu Oct 20 05:53:21 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 827AF16A41F; Thu, 20 Oct 2005 05:53:21 +0000 (GMT) (envelope-from bde@zeta.org.au) Received: from mailout1.pacific.net.au (mailout1.pacific.net.au [61.8.0.84]) by mx1.FreeBSD.org (Postfix) with ESMTP id D547043D62; Thu, 20 Oct 2005 05:53:20 +0000 (GMT) (envelope-from bde@zeta.org.au) Received: from mailproxy1.pacific.net.au (mailproxy1.pacific.net.au [61.8.0.86]) by mailout1.pacific.net.au (8.13.4/8.13.4/Debian-3) with ESMTP id j9K5rGV8005487; Thu, 20 Oct 2005 15:53:16 +1000 Received: from katana.zip.com.au (katana.zip.com.au [61.8.7.246]) by mailproxy1.pacific.net.au (8.13.4/8.13.4/Debian-3) with ESMTP id j9K5rEG5013000; Thu, 20 Oct 2005 15:53:15 +1000 Date: Thu, 20 Oct 2005 15:53:15 +1000 (EST) From: Bruce Evans X-X-Sender: bde@delplex.bde.org To: John Baldwin In-Reply-To: <200510181101.03956.jhb@freebsd.org> Message-ID: <20051020154709.U99720@delplex.bde.org> References: <200510172310.j9HNAVPL013057@repoman.freebsd.org> <20051018094402.A29138@grasshopper.cs.duke.edu> <200510181101.03956.jhb@freebsd.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed 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 05:53:21 -0000 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. Bruce