Date: Fri, 23 Aug 2002 23:21:33 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: John Polstra <jdp@polstra.com> Cc: current@freebsd.org Subject: Re: how to compute the skew between TSC in SMP systems ? Message-ID: <30293.1030137693@critter.freebsd.dk> In-Reply-To: Your message of "Fri, 23 Aug 2002 14:14:08 PDT." <200208232114.g7NLE80E087984@vashon.polstra.com>
next in thread | previous in thread | raw e-mail | index | archive | help
In message <200208232114.g7NLE80E087984@vashon.polstra.com>, John Polstra write s: >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. Was this before or after APM, ACPI, SpeedStep and all the other crap ruined the TSC as a timecounting device ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?30293.1030137693>