Messages in this thread | | | Subject | Re: BUG: using smp_processor_id() in preemptible [00000000] code: icedove-bin/5449 | From | Peter Zijlstra <> | Date | Thu, 27 May 2010 08:46:38 +0200 |
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On Wed, 2010-05-26 at 16:02 -0700, Andrew Morton wrote:
> How is anyone supposed to use this? What are the semantics of this > thing? What are the units of its return value? What is the base value > of its return value? Does it return different times on different CPUs? > I assume so, otherwise why does sched_clock_cpu() exist? <looks at > the sched_clock_cpu() documentation, collapses in giggles>
The point of the whole sched_clock_cpu() thing is to provide a fairly high resolution clock with bounded drift between cpus.
It also promises to be monotonic per cpu argument, that is, sched_clock_cpu(j) will, for a constant j always return a monotonic increasing timestamp.
It doesn't make much promises about its base (although people tend to want it to start at 0 on boot, but the users really shouldn't care).
sched_clock() doesn't promise either bounded drift between cpus nor monotonicity.
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