Re: [PATCH] sched: Support current clocksource handling infallback sched_clock().

From: Peter Zijlstra
Date: Wed May 27 2009 - 02:59:23 EST

On Tue, 2009-05-26 at 16:00 -0700, john stultz wrote:

> Sure, I guess what I'm trying to pull out here is that should we try to
> create some OK_FOR_SCHED_CLOCK flag for clocksources, and then we try to
> make this generic so other arches can add that flag and be done, what is
> the guidance we want to give to arch maintainers for setting that flag?
> 1) Has to be very very fast. Can we put a number on this? 50ns to read?

I'd express it in cpu cycles, but not sure, the very fastest the arch
has :-) Just tell people this is in their scheduling hot-path and they
might understand.

> 2) How long does it have to be monotonic for?

Forever? (per cpu)

> Is it ok if it wraps every few seconds?

No, if it wraps it needs to wrap on u64.

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