From owner-freebsd-current@FreeBSD.ORG Fri Aug 13 16:49:21 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 99A2416A4CE for ; Fri, 13 Aug 2004 16:49:21 +0000 (GMT) Received: from duke.cs.duke.edu (duke.cs.duke.edu [152.3.140.1]) by mx1.FreeBSD.org (Postfix) with ESMTP id 1BABA43D53 for ; Fri, 13 Aug 2004 16:49:21 +0000 (GMT) (envelope-from gallatin@cs.duke.edu) Received: from grasshopper.cs.duke.edu (grasshopper.cs.duke.edu [152.3.145.30]) by duke.cs.duke.edu (8.12.10/8.12.10) with ESMTP id i7DGnKJt000870 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Fri, 13 Aug 2004 12:49:20 -0400 (EDT) Received: (from gallatin@localhost) by grasshopper.cs.duke.edu (8.12.9p2/8.12.9/Submit) id i7DGnF0C090731; Fri, 13 Aug 2004 12:49:15 -0400 (EDT) (envelope-from gallatin) From: Andrew Gallatin MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <16668.61707.474283.639200@grasshopper.cs.duke.edu> Date: Fri, 13 Aug 2004 12:49:15 -0400 (EDT) To: freebsd-current@freebsd.org X-Mailer: VM 6.75 under 21.1 (patch 12) "Channel Islands" XEmacs Lucid Subject: Is the TSC timecounter safe on SMP system? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Aug 2004 16:49:21 -0000 I have a system where the TSC timecounter is quite a bit more accurate (or perhaps its just much cheaper) than the ACPI timecounter. This is a single CPU, HTT system running an SMP kernel. A simple program which calls gettimeofday() in a tight loop, looking for the microseconds to change sees ~998,000 microsecond updates/sec with kern.timecounter.hardware=TSC, and 28,500 updates/sec with ACPI-safe. 1) Is it safe to switch to TSC? 2) If yes, would it be safe to switch to TSC if this was a real SMP system with multiple physical cpus? Thanks, Drew