On Wed, 28 Feb 2018, Felipe Balbi wrote: > Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes: > > Enable the hrtimer and scheduling tracepoints. That should give you a hint > > what's going on. > > Thanks, that does give me a lot more information. So here you go: > > rtctest-1348 [003] d..2 313.766141: hrtimer_start: hrtimer=00000000667ce595 function=rtc_pie_update_irq expires=313573983010 softexpires=313573983010 mode=REL > <idle>-0 [003] d.h1 313.767189: hrtimer_expire_entry: hrtimer=00000000667ce595 function=rtc_pie_update_irq now=313574053764 > > We still have a 70754 nS deviation. After changing to absolute time, > the deviation remains: > > <idle>-0 [000] dNh2 29.303251: hrtimer_start: hrtimer=000000006858b496 function=rtc_pie_update_irq expires=28765551360 softexpires=28765551360 mode=ABS > <idle>-0 [000] d.h1 29.303565: hrtimer_expire_entry: hrtimer=000000006858b496 function=rtc_pie_update_irq now=28765621916 Changing REL/ABS in the kernel does not make a difference because periodic mode just forwards by period so even if the first timer is started with REL it results in a absolute timeline. What I meant is the user space measurement as it cannot figure out when the first event was supposed to happen so it's hard to calculate latency information. The interesting information is that the timer fires late and the system is idle. Now the question is in which idle state did the machine go? Wake up from deeper C-states can be slow. On my laptop the wakeup latencies are: POLL 0 C1 2 C1E 10 C3 33 C6 133 C7S 166 C8 300 C9 600 C10 2600 All numbers in micro seconds! What happens if you load the system or restrict C-States? Thanks, tglx
