Re: [PATCH] RFC: nomadik: expand timesource to 63 bits

Nicolas Pitre
2010-11-12T19:18:36Z

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On Fri, 12 Nov 2010, Linus Walleij wrote:

> Thomas Gleixner wrote:
> > On Fri, 12 Nov 2010, Linus Walleij wrote:
> >> Uwe Kleine-König wrote:
> >>
> >>> Instead of implementing sched_clock for each architecture seperatly,
> >>> wouldn't it be nice to have a generic sched_clock that uses the
> >>> architecture's clocksource? I tried to implement that some time ago,
> >>> but tglx shoot it down because of locking problems.
> >> I was and still am a big fan of this approach, I am willing to help
> >> testing it if you want to dust off this patch set...
> >
> > sched_clock is not necessarily the same as the current clocksource.
>
> IIRC Uwe:s approach was that if and only if you would want to use
> the clocksource for sched_clock() you provide a special flag on
> the clocksource, and it will be attempted to be used for sched_clock().
>
> Incidentally the dual use of a single free-running timer as both
> single clocksource and sched_clock() baseline seem to creep up in
> a lot of embedded platforms...

Sure, but the computations and associated cost around that free running
timer are not the same in both cases.

Nicolas