linux-kernel - Re: High scheduler wake up times

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Date:	Sun, 31 Jan 2010 14:50:43 -0600
From:	Shawn Bohrer <shawn.bohrer@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: High scheduler wake up times

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 2.6.32.7, 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.

Thanks,
Shawn
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