linux/kernel/time
Venkatesh Pallipadi 83cd4fe27a sched: Change nohz idle load balancing logic to push model
In the new push model, all idle CPUs indeed go into nohz mode. There is
still the concept of idle load balancer (performing the load balancing
on behalf of all the idle cpu's in the system). Busy CPU kicks the nohz
balancer when any of the nohz CPUs need idle load balancing.
The kickee CPU does the idle load balancing on behalf of all idle CPUs
instead of the normal idle balance.

This addresses the below two problems with the current nohz ilb logic:
* the idle load balancer continued to have periodic ticks during idle and
  wokeup frequently, even though it did not have any rebalancing to do on
  behalf of any of the idle CPUs.
* On x86 and CPUs that have APIC timer stoppage on idle CPUs, this
  periodic wakeup can result in a periodic additional interrupt on a CPU
  doing the timer broadcast.

Also currently we are migrating the unpinned timers from an idle to the cpu
doing idle load balancing (when all the cpus in the system are idle,
there is no idle load balancing cpu and timers get added to the same idle cpu
where the request was made. So the existing optimization works only on semi idle
system).

And In semi idle system, we no longer have periodic ticks on the idle load
balancer CPU. Using that cpu will add more delays to the timers than intended
(as that cpu's timer base may not be uptodate wrt jiffies etc). This was
causing mysterious slowdowns during boot etc.

For now, in the semi idle case, use the nearest busy cpu for migrating timers
from an idle cpu.  This is good for power-savings anyway.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <1274486981.2840.46.camel@sbs-t61.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-06-09 10:34:52 +02:00
..
clockevents.c clockevent: Don't remove broadcast device when cpu is dead 2010-01-18 14:44:50 +01:00
clocksource.c clocksource: Add clocksource_register_hz/khz interface 2010-05-10 14:24:26 +02:00
jiffies.c clocksource: Cleanup clocksource selection 2009-08-15 10:55:46 +02:00
Kconfig Kconfig: eliminate "def_bool n" constructs 2008-10-16 11:21:31 -07:00
Makefile time: add function to convert between calendar time and broken-down time for universal use 2009-09-24 07:20:56 -07:00
ntp.c ntp: Make time_adjust static 2010-03-23 17:19:37 +01:00
tick-broadcast.c clockevents: Convert to raw_spinlock 2009-12-14 23:55:34 +01:00
tick-common.c clockevents: Convert to raw_spinlock 2009-12-14 23:55:34 +01:00
tick-internal.h clockevents: Make tick_device_lock static 2009-12-14 23:55:34 +01:00
tick-oneshot.c clockevents: Sanitize min_delta_ns adjustment and prevent overflows 2010-03-12 19:10:29 +01:00
tick-sched.c sched: Change nohz idle load balancing logic to push model 2010-06-09 10:34:52 +02:00
timecompare.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
timeconv.c time: add function to convert between calendar time and broken-down time for universal use 2009-09-24 07:20:56 -07:00
timekeeping.c Merge branch 'linus' into timers/core 2010-05-10 14:20:42 +02:00
timer_list.c sched: Intoduce get_cpu_iowait_time_us() 2010-05-09 19:35:27 +02:00
timer_stats.c hrtimers: Convert to raw_spinlocks 2009-12-14 23:55:34 +01:00