Messages in this thread | | | Date | Thu, 11 Nov 2010 13:31:52 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [PATCH] RFC: nomadik: expand timesource to 63 bits |
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On Thu, 11 Nov 2010, Thomas Gleixner wrote:
> 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.
You still have to make sure you get out of idle before 16 secs has passed.
Nicolas
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