linux-kernel - [REGRESSION 2.6.28-rc2-git3] lots of extra timer interrupts costing 2W

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Message-Id: <E1KvN6w-0002QE-E3@closure.thunk.org>
Date:	Wed, 29 Oct 2008 22:18:10 -0400
From:	"Theodore Ts'o" <tytso@....edu>
To:	linux-kernel@...r.kernel.org
Subject: [REGRESSION 2.6.28-rc2-git3] lots of extra timer interrupts costing 2W

I've noticed that sometime between 2.6.27-git7 and 2.6.28-rc2-git3,
powertop is reporting a huge number of excess timer interrupts on my
x61s laptop:

Wakeups-from-idle per second : 617.8    interval: 3.1s
no ACPI power usage estimate available

Top causes for wakeups:
  71.3% (543.7)       <interrupt> : extra timer interrupt 
  13.5% (103.0)     <kernel core> : hrtimer_start_expires (tick_sched_timer) 
   7.2% ( 55.0)      <kernel IPI> : Rescheduling interrupts 
   1.7% ( 13.0)    gnome-terminal : hrtimer_start_expires (hrtimer_wakeup) 
   1.4% ( 10.3)       <interrupt> : PS/2 keyboard/mouse/touchpad 
   1.1% (  8.3)       <interrupt> : ahci
   0.4% (  3.3)   multiload-apple : hrtimer_start_expires (hrtimer_wakeup)
   0.3% (  2.7)              Xorg : hrtimer_start (it_real_fn)


This is costing me an extra 2 Watts or so.   Does this ring a bell with
anyone, before I start trying to bisect this problem?

						- Ted
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