Re: high res timestamps and SMP

From: Mikael Pettersson
Date: Thu Nov 20 2003 - 05:22:18 EST


john stultz writes:
> On Wed, 2003-11-19 at 14:40, Chris Friesen wrote:
> > We have a requirement to have high-res timestamps available on SMP systems.
...
> o PPC has a nice in-cpu time-base register (ppc folks, feel free to
> smack or correct me on this) which is driven off the bus-clock and is
> synced in hardware.

Last time I checked, all 32-bit PowerPC chips ran that clock at 1/4
of the bus clock speed.

That may be adequate for time-of-day and I/O delays and such, but
it's worthless for timestamps or performance measurements.

It's possible to count core clocks via a performance counter, but
I don't know if they are synced between CPUs.
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