Date: Thu, 17 May 2001 17:44:28 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Matt Dillon <dillon@earth.backplane.com> Cc: Terry Lambert <tlambert2@mindspring.com>, dave <dleimbac@earthlink.net>, freebsd-questions@FreeBSD.ORG, arch@FreeBSD.ORG Subject: Re: Gettimeofday Again... Message-ID: <Pine.BSF.4.21.0105171727150.15884-100000@besplex.bde.org> In-Reply-To: <200105161743.f4GHhEl72847@earth.backplane.com>
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On Wed, 16 May 2001, Matt Dillon wrote: > I just ran the test using the default timecounter on a 4.3 box (P3). > timercounter.method was 0, timecounter.hardware was i8254. In > that case the itimer was about 4 times faster. So this was using > the 'slow' itimer as you indicate below. Unfortunately, 4.3 (like all 4.x) defaults to the pessimized configuration of always using the i8254 for no good reason. This is because apm is configured in GENERIC, and clock.c disables the TSC if apm is configured even if apm is disabled (as it is by default). -current achives the same pessimization by enabling apm by default although clock.c is smarter. > 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). Efficiency is not the only advantage of the TSC timecounter. It has a higher resolution and is more robust if interrupt latency is high. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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