Date: Sat, 16 Dec 2006 15:31:44 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Joseph Koshy" <joseph.koshy@gmail.com> Cc: freebsd-hackers@freebsd.org, mldodson@houston.rr.com Subject: Re: "Syncing cpus" on a multi-cpu, dual core system Message-ID: <200612162331.kBGNViQ9035504@apollo.backplane.com> References: <200612141437.28724.mldodson@houston.rr.com> <84dead720612150950p33c9c35erffe4adbab7227e68@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200612162331.kBGNViQ9035504>