In message <[EMAIL PROTECTED]>, Luoqi Chen writes:

>Second, the listed reason for not using TSC on SMP is the inability
>to synchronize TSCs on all cpus. My question is, is it really necessary?

Strictly speaking no, it isn't necessary, but unless they are in sync
the timekeeping code gets very complex.  See Dave "ntp" Mills code to
hold them in sync.

>TSC is initialized to 0 at hardware reset, which should happen to all CPUs
>at the same time (invalid assumption?), in another words, all TSCs should be
>automatically synchronized.

They are not.  The PLL is local to each cpu and every single
clock-stop/start event has then inching away from each other because
the on-chip VCO is very temperature dependent.  Furthermore Linux
people have found sufficiently many cases where the counters are
not in sync after the BIOS is done.

Poul-Henning Kamp             FreeBSD coreteam member
[EMAIL PROTECTED]               "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!

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