Messages in this thread | | | Subject | Re: [PATCH] sched: Support current clocksource handling in fallback sched_clock(). | From | Peter Zijlstra <> | Date | Tue, 26 May 2009 16:50:09 +0200 |
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On Tue, 2009-05-26 at 23:43 +0900, Paul Mundt wrote: > > Else you might want an additional criteria, like > > cyc2ns(1) (much less than) jiffies_to_usecs(1)*1000 > > (however you do that the best way) > > so you don't pick something > > that isn't substantially faster than the jiffy counter atleast? > > > This rather defeats the purpose of sched_clock() being fast. If we want > to add a flag that means this in to the clocksource instead of consulting > the rating, that is fine with me too. I know which clocksources I prefer > to use for a sched_clock() and they are all better than jiffies. The > semantics of how we tell sched_clock() that are not so important. Rating > seemed like a good choice from the documentation in struct clocksource at > least.
Am I confused or are we talking about fast HZ vs fast cycles?
sched_clock() should be fast cycles, that is, we don't want to read a clock that takes about 1000 cycles.
sched_clock() is about providing a high resolution clock that is fast (low cycle count) to acquire, and need not be strictly monotonic on smp.
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