Date: Fri, 23 Aug 2002 14:14:08 -0700 (PDT) From: John Polstra <jdp@polstra.com> To: current@freebsd.org Cc: phk@critter.freebsd.dk Subject: Re: how to compute the skew between TSC in SMP systems ? Message-ID: <200208232114.g7NLE80E087984@vashon.polstra.com> In-Reply-To: <29486.1030136549@critter.freebsd.dk> References: <29486.1030136549@critter.freebsd.dk>
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In article <29486.1030136549@critter.freebsd.dk>, Poul-Henning Kamp <phk@critter.freebsd.dk> wrote: > In message <20020823134410.A81962@iguana.icir.org>, Luigi Rizzo writes: > >does anyone have an idea on how to determine the skew between > >TSC content in the various processors on an SMP box ? > > On i386: It cannot be reliably done. Been there, tried that. Well ... you can come pretty close. The BSD/OS kernel has code (conditioned on option SMP_DEBUG) that manages to sync up all TSCs in an N-CPU system such that the measured difference between the extremes is less than 100 counts. John -- John Polstra John D. Polstra & Co., Inc. Seattle, Washington USA "Disappointment is a good sign of basic intelligence." -- Chögyam Trungpa To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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