> The question is: "what assumptions can be made?" On the i386
> architecture, will all cycle counters start at the same moment, and
> will they be bound to the same oscillator? If not one has to
> calibrate each CPU, and remember the cycle counter of each CPU during
> timer interrupt. When getting the time one must find the cycle
> counter of the own CPU and subtract that counter at the last
> interrupt to get the difference. Other architectures maybe even worse.
the newest SMP patch does exactly this. _Most_ boards have synchron cycle
counters, but not all ... We explicitly synchronize the cycle counters at
early bootup time. So i think you should safely assume that they are
synchron.
> Colin Plumb suggested to synchronize the cycle counters on i386
> architecture, assuming they'll remain in sync. This would make the
> time code much easier, but break things terrible, if the counters
(yep, i've implemented this after Colin proved via user-space tools that
some systems are not synchron.) Also, it's guaranteed that the CPUs stay
synchron once synchronized.
-- mingo
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