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Date: Sat, 16 Dec 2006 15:31:44 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
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To: "Joseph Koshy" <joseph.koshy@gmail.com>
References: <200612141437.28724.mldodson@houston.rr.com>
	<84dead720612150950p33c9c35erffe4adbab7227e68@mail.gmail.com>
Cc: freebsd-hackers@freebsd.org, mldodson@houston.rr.com
Subject: Re: "Syncing cpus" on a multi-cpu, dual core system
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    The TSCs for each individual cpu core can drift relative to each other,
    even on multi-core chips like AMD X2s.  This only effects code which
    uses the TSC, which isn't a whole lot.  They need to be synchronized
    with each other (by calculating the drift and correcting for it) when
    using the TSC to log events, such as KTR logging might do.  Since the
    TSC runs off the PLL, the drift rate will change based on the temperature
    of each core.

    I'm not sure whether the LAPIC timers can be depended upon to operate
    from the same physical clock source or not (i.e. whether they drift 
    relative to each other or not).  I haven't tested them for that.

						-Matt