Messages in this thread | | | Date | Thu, 11 Nov 2010 12:05:03 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] RFC: nomadik: expand timesource to 63 bits |
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On Thu, 11 Nov 2010, Linus Walleij wrote:
> Thomas Gleixner wrote: > > > There is only one caveat. When nohz is on and you sleep longer than 16 > > seconds then the limitation we have in place does not work anymore, as > > it would say that the long sleep time is less than the 63bit > > wraparound time. With 32bit clocksource it limits the sleep correclty > > to avoid the clocksource wrap issue. > > Hm! So the .mask has that side effect (as I suspected), and with > this the sleep will be limited to what time you can get into 63 bits > (2200 years). And we sure want NOHZ... > > But if I complement the solution with the keepwarm() timer from > Orion doing just a dummy read() on the clocksource every say 15 secs > it will work even if the system sleeps for so long.
Well, you don't need the keepwarm() timer, if you just call sched_clock() in the idle wakeup path, so the magic in the NOHZ code will ensure that you reread the thing timely.
Thanks,
tglx
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