Date: Thu, 10 Apr 2008 21:45:41 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Maxim Sobolev <sobomax@FreeBSD.org> Cc: gnn@FreeBSD.org, Kris Kennaway <kris@FreeBSD.org>, current@FreeBSD.org Subject: Re: TSC Timecounter and multi-core/SMP Message-ID: <1248.1207863941@critter.freebsd.dk> In-Reply-To: Your message of "Thu, 10 Apr 2008 13:52:28 MST." <47FE7E0C.4070801@FreeBSD.org>
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In message <47FE7E0C.4070801@FreeBSD.org>, Maxim Sobolev writes: >Kris Kennaway wrote: >> gnn@freebsd.org wrote: >>> Howdy, >>> >>> Is the TSC timecounter synchronized across multiple cores and/or >>> processors? A quick search seems to indicate it's not but I'd like to >>> find a definitive reference on the TSC. >> >> Modern Intel systems tend to be synchronized, in my experience. > >I really doubt they are. As far as I know newest milti-core chips can >modulate frequency of even suspend individual cores independently of >each other, which would make such synchronization difficult to maintain >if the power management is on. P4 (and I think most newer chips) have a TSC that runs independent of the cpu clock frequency, and supposedly, always at constant rate. -- 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.
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