Messages in this thread |  | | Date | Thu, 16 Jan 2014 10:46:22 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [QUERY]: Is using CPU hotplug right for isolating CPUs? |
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On Thu, 16 Jan 2014, Viresh Kumar wrote:
> On 15 January 2014 22:47, Frederic Weisbecker <fweisbec@gmail.com> wrote: > > Are you sure about that? NO_HZ_FULL shouldn't touch much hrtimers. > > Those are independant from the tick. > > > > Although some of them seem to rely on the softirq, but that seem to > > concern the tick hrtimer only. > > To make it clear I was talking about the hrtimer used by tick_sched_timer. > I have crossed checked which timers are active on isolated CPU from > /proc/timer_list and it gave on tick_sched_timer's hrtimer. > > In the attached trace (dft.txt), see these locations: > - Line 252: Time 302.573881: we scheduled the hrtimer for 300 seconds > ahead of current time. > - Line 254, 258, 262, 330, 334: We got interruptions continuously after > ~90 seconds and this looked to be a case of timer's counter overflow. > Isn't it? (I have removed some lines towards the end of this file to make > it shorter, though dft.dat is untouched)
Just do the math.
max reload value / timer freq = max time span
So:
0x7fffffff / 24MHz = 89.478485 sec
Nothing to do here except to get rid of the requirement to arm the timer at all.
Thanks,
tglx
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