Re: [discuss] Re: [PATCH] Allow all Opteron processors to change pstate at same time

From: Andi Kleen
Date: Wed Jul 26 2006 - 14:57:06 EST

> In contrast, the same machine running with TSC and standard
> PN! sees massive drift, upwards of an hour, within an hour.

Do you see the same drift when you lock date on a single CPU
with taskset?

> If the TSCnow! patch reduces measured drift down to a second
> a week, would you consider that acceptable?

No because even one second a week will break timing badly
over time.

I believe the only good solution unless hardware helps would
be to use per CPU TSC offsets as discussed earlier. Even that
is a bit risky because there can be still very small drifts,
but they should be limited by a clock tick error max and
might work out.


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