From owner-freebsd-arch Thu May 17 5:23:49 2001 Delivered-To: freebsd-arch@freebsd.org Received: from mailman.zeta.org.au (mailman.zeta.org.au [203.26.10.16]) by hub.freebsd.org (Postfix) with ESMTP id ADD8337B422; Thu, 17 May 2001 05:23:44 -0700 (PDT) (envelope-from bde@zeta.org.au) Received: from bde.zeta.org.au (bde.zeta.org.au [203.2.228.102]) by mailman.zeta.org.au (8.9.3/8.8.7) with ESMTP id WAA06692; Thu, 17 May 2001 22:23:41 +1000 Date: Thu, 17 May 2001 22:22:13 +1000 (EST) From: Bruce Evans X-Sender: bde@besplex.bde.org To: Mike Smith Cc: freebsd-questions@FreeBSD.ORG, arch@FreeBSD.ORG Subject: Re: Gettimeofday Again... In-Reply-To: <200105170813.f4H8DhE01424@mass.dis.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Thu, 17 May 2001, Mike Smith wrote: > > > I don't change the timercounter method defaults, and I sure hope you > > > aren't advocating that people change their timecounter defaults. If > > > the TSC is a reasonable default, the system should figure it out and > > > use it without requiring intervention. > > > > It's only a reasonable default if apm (or possibly acpica) is configured > > (and used). > > The TSC is never a reasonable default; there is no good way to be certain > that the TSC is and/or will remain stable. Even with ACPI, you can't be > entirely sure. This must be why Linux uses it by default ;-). See linux/arch/i386/config.in, option CONFIG_X86_TSC. Linux-2.4.1 still only uses it to give an offset from the last i8254 clock interrupt, like FreeBSD used to do 3+ years ago before timecounters. This may limit the errors from the TSC frequency changing to between -10 and 0 msec (hopefully the frequency is calibrated when it is as large as possible; then if it slows down down you underestimate the offset). Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message