nohz regression with upstream git

[Venki Pallipadi <venkatesh.pallipadi@intel.com>]

Thomas,

I am seeing a nohz regression on one of my dual core mobile test boxes.
With 2.6.27 tickless idle works fine.
With latest git, I see ~2000 interrupts per second (HZ=1000), even when idle.

git bisect points towards

commit fb02fbc14d17837b4b7b02dbb36142c16a7bf208
Author: Thomas Gleixner <tglx@linutronix.de>
Date:   Fri Oct 17 10:01:23 2008 +0200

    NOHZ: restart tick device from irq_enter()


And good powertop data

PowerTOP 1.10    (C) 2007, 2008 Intel Corporation 

Collecting data for 15 seconds 


Cn	          Avg residency
C0 (cpu running)        ( 0.1%)
polling		  0.0ms ( 0.0%)
C1		  0.0ms ( 0.0%)
C3		 18.6ms (99.9%)
P-states (frequencies)
  2.21 Ghz     0.0%
  2.21 Ghz     0.0%
  1.60 Ghz     0.0%
   800 Mhz   100.0%
Wakeups-from-idle per second : 53.9	interval: 15.0s
no ACPI power usage estimate available
Top causes for wakeups:
  65.5% ( 32.6)       <interrupt> : extra timer interrupt 
  16.7% (  8.3)      <kernel IPI> : Rescheduling interrupts 
   3.3% (  1.7)            kacpid : schedule_timeout (process_timeout) 
   2.8% (  1.4)       <interrupt> : ata_piix, uhci_hcd:usb4 
   2.3% (  1.1)       <interrupt> : eth1 
   2.0% (  1.0)     <kernel core> : enqueue_task_rt (sched_rt_period_timer) 
   1.9% (  0.9)     <kernel core> : schedule_delayed_work_on (delayed_work_timer_fn) 
   1.1% (  0.5)     <kernel core> : neigh_table_init_no_netlink (neigh_periodic_timer) 
   1.1% (  0.5)     <kernel core> : e1000_intr_msi (e1000_watchdog) 
   0.7% (  0.3)      <kernel IPI> : Function call interrupts 
   0.4% (  0.2)          events/1 : __netdev_watchdog_up (dev_watchdog) 
   0.4% (  0.2)          sendmail : schedule_timeout (process_timeout) 
   0.4% (  0.2)     <kernel core> : page_writeback_init (wb_timer_fn) 
   0.3% (  0.1)        kerneloops : schedule_timeout (process_timeout) 
   0.3% (  0.1)        kerneloops : do_nanosleep (hrtimer_wakeup) 
   0.1% (  0.1)              sshd : sk_reset_timer (tcp_write_timer) 
   0.1% (  0.1)          events/1 : queue_delayed_work (delayed_work_timer_fn) 
   0.1% (  0.1)             mount : start_this_handle (commit_timeout) 
   0.1% (  0.1)     <kernel core> : queue_delayed_work (delayed_work_timer_fn) 
   0.1% (  0.1)   hald-addon-stor : schedule_timeout (process_timeout) 
   0.1% (  0.1)     <kernel core> : neigh_add_timer (neigh_timer_handler) 
   0.1% (  0.1)     <kernel core> : sk_reset_timer (tcp_delack_timer) 



and bad powertop data


PowerTOP 1.10    (C) 2007, 2008 Intel Corporation 

Collecting data for 15 seconds 


Cn	          Avg residency
C0 (cpu running)        ( 5.6%)
polling		  0.0ms ( 0.0%)
C1		  1.2ms ( 0.0%)
C3		  0.5ms (94.4%)
P-states (frequencies)
  2.21 Ghz     0.0%
  2.21 Ghz     0.0%
  1.60 Ghz     0.0%
   800 Mhz   100.0%
Wakeups-from-idle per second : 1919.6	interval: 15.0s
no ACPI power usage estimate available
Top causes for wakeups:
  99.0% (1902.4)       <interrupt> : extra timer interrupt 
   0.3% (  6.1)      <kernel IPI> : Rescheduling interrupts 
   0.3% (  5.6)       <interrupt> : acpi 
   0.1% (  1.4)       <interrupt> : ata_piix, uhci_hcd:usb4 
   0.1% (  1.1)       <interrupt> : ata_piix, ehci_hcd:usb1, uhci_hcd:usb6 
   0.1% (  1.1)       <interrupt> : eth1 
   0.1% (  1.0)     <kernel core> : enqueue_task_rt (sched_rt_period_timer) 
   0.0% (  0.9)     <kernel core> : schedule_delayed_work_on (delayed_work_timer_fn) 
   0.0% (  0.5)    NetworkManager : e1000_intr_msi (e1000_watchdog) 
   0.0% (  0.5)     <kernel core> : neigh_table_init_no_netlink (neigh_periodic_timer) 
   0.0% (  0.2)     <kernel core> : page_writeback_init (wb_timer_fn) 
   0.0% (  0.2)          events/1 : __netdev_watchdog_up (dev_watchdog) 
   0.0% (  0.2)          sendmail : schedule_timeout (process_timeout) 
   0.0% (  0.1)        kerneloops : schedule_timeout (process_timeout) 
   0.0% (  0.1)          events/0 : sk_reset_timer (tcp_delack_timer) 
   0.0% (  0.1)              sshd : sk_reset_timer (tcp_write_timer) 
   0.0% (  0.1)          events/0 : neigh_add_timer (neigh_timer_handler) 
   0.0% (  0.1)          rsyslogd : schedule_timeout (process_timeout) 
   0.0% (  0.1)           rpcbind : schedule_timeout (process_timeout) 
   0.0% (  0.1)             mount : start_this_handle (commit_timeout) 
   0.0% (  0.1)              hald : schedule_timeout (process_timeout) 
   0.0% (  0.1)             crond : do_nanosleep (hrtimer_wakeup) 
   0.0% (  0.1)     <kernel core> : queue_delayed_work (delayed_work_timer_fn) 
   0.0% (  0.1)   hald-addon-stor : schedule_timeout (process_timeout) 


Not sure what is so specific about this platform that causes this problem.
Its a regular Centrino 2 development box.

I will poke more at this tomorrow. But, wanted to pass the info on to you
before calling it a night.

Let me know if you need any more info on this.

Thanks,
Venki