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    SubjectRe: [PATCH] U300 sched_clock implementation
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    On Mon, 2009-06-01 at 09:46 +0200, Linus Walleij wrote:
    > 2009/5/25 Peter Zijlstra <peterz@infradead.org>:
    > > On Mon, 2009-05-25 at 14:13 +0200, Linus Walleij wrote:
    > >> 2009/5/24 Peter Zijlstra <peterz@infradead.org>:
    > >>
    > >> > On Sat, 2009-05-23 at 23:46 +0200, Linus Walleij wrote:
    > >> >
    > >> >> This overrides the global sched_clock() symbol in the Linux
    > >> >> scheduler with a local implementation which takes advantage of
    > >> >> the timesource in U300 giving a scheduling resolution of 1us. The
    > >> >> solution is the same as found in the OMAP2 core code.
    > >> >
    > >> > We assume sched_clock() to return time in ns (e-9) resolution.
    > >>
    > >> Yep okay and in this case:
    > >>
    > >> >> + ret = (unsigned long long) u300_get_cycles();
    > >> >> + ret = (ret * clocksource_u300_1mhz.mult_orig) >>
    > >> >> + clocksource_u300_1mhz.shift;
    > >> >> + return ret;
    > >>
    > >> (mult_orig >> shift) == 1000
    > >
    > > Ah, ok -- missed that little detail ;-)
    > >
    > >> So for each cycle in cyclecount register we return 1000 * cycles
    > >> i.e 1000ns.
    > >>
    > >> If it looks nicer we can of course simply:
    > >> return (unsigned long long) u300_get_cycles * 1000;
    > >>
    > >> But the question here is whether this resolution is enough for
    > >> sched_clock() or if it is irrelevant to override sched_clock()
    > >> if it cannot schedule with better precision than 1000 ns.
    > >
    > > No anything better than jiffies is good, 1us certainly is worth the
    > > trouble.
    >
    > Can I interpret this as Acked-by: Peter Zijlstra <peterz@infradead.org> ?

    I think its best if we continue with the patch Paul Mundt has been
    proposing.


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