Date: Wed, 22 Sep 1999 07:55:36 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Luoqi Chen <luoqi@watermarkgroup.com> Cc: current@FreeBSD.ORG, smp@FreeBSD.ORG Subject: Re: Testers please! Message-ID: <32777.937979736@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 21 Sep 1999 20:25:08 EDT." <199909220025.UAA25595@lor.watermarkgroup.com>
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In message <199909220025.UAA25595@lor.watermarkgroup.com>, Luoqi Chen writes: >Second, the listed reason for not using TSC on SMP is the inability >to synchronize TSCs on all cpus. My question is, is it really necessary? Strictly speaking no, it isn't necessary, but unless they are in sync the timekeeping code gets very complex. See Dave "ntp" Mills code to hold them in sync. >TSC is initialized to 0 at hardware reset, which should happen to all CPUs >at the same time (invalid assumption?), in another words, all TSCs should be >automatically synchronized. They are not. The PLL is local to each cpu and every single clock-stop/start event has then inching away from each other because the on-chip VCO is very temperature dependent. Furthermore Linux people have found sufficiently many cases where the counters are not in sync after the BIOS is done. -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." FreeBSD -- It will take a long time before progress goes too far! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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