Re: High scheduler wake up times

From: Shawn Bohrer
Date: Sun Jan 31 2010 - 15:51:20 EST

On Sun, Jan 31, 2010 at 10:28:46AM -0800, Arjan van de Ven wrote:
> can you run powertop during your workload? maybe you're getting hit by
> some C state exit latencies tilting the rounding over the top just too
> many times...

Running 50 of the example processes and powertop on, with the
performance cpu governor:

Cn Avg residency P-states (frequencies)
C0 (cpu running) (24.7%)
polling 0.0ms ( 0.0%)
C1 mwait 0.3ms ( 0.0%)
C3 mwait 0.8ms (75.3%)

Wakeups-from-idle per second : 980.1 interval: 10.0s
no ACPI power usage estimate available

Top causes for wakeups:
76.2% (45066.9) worker_process : sys_epoll_wait (process_timeout)
22.0% (13039.2) <kernel core> : hrtimer_start_range_ns (tick_sched_timer)
1.5% (892.7) kipmi0 : schedule_timeout_interruptible (process_timeout)
0.2% (105.0) <kernel core> : add_timer (smi_timeout)
0.0% ( 10.5) <interrupt> : ata_piix
0.0% ( 10.1) <kernel core> : ipmi_timeout (ipmi_timeout)

I also tried booting with processor.max_cstate=0 which causes powertop
to no longer show any cstate information but I assumed that would keep
me fixed at C0. Booting with processor.max_cstate=0 didn't seem to make
any difference.

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