sched: using avg_idle to detect bursty wakeup

Sleeping task has no utiliation, when they were bursty waked up, the
zero utilization make scheduler out of balance, like aim7 benchmark.

rq->avg_idle is 'to used to accommodate bursty loads in a dirt simple
dirt cheap manner' -- Mike Galbraith.

With this cheap and smart bursty indicator, we can find the wake up
burst, and use nr_running as instant utilization in this scenario.

For other scenarios, we still use the precise CPU utilization to
judage if a domain is eligible for power scheduling.

Thanks for Mike Galbraith's idea!

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: packing transitory tasks in wakeup power balancing

If the waked task is transitory enough, it will has a chance to be
packed into a cpu which is busy but still has time to care it.

For powersaving policy, only the history util < 25% task has chance to
be packed. If there is no cpu eligible to handle it, will use a idlest
cpu in leader group.

Morten Rasmussen catch a type bug. And PeterZ reminder to consider
rt_util. thanks you!

Inspired-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: add power/performance balance allow flag

If a sched domain is idle enough for regular power balance, LBF_POWER_BAL
will be set, LBF_PERF_BAL will be clean. If a sched domain is busy,
their value will be set oppositely.

If the domain is suitable for power balance, but balance should not
be down by this cpu(this cpu is already idle or full), both of flags
are cleared to wait a suitable cpu to do power balance.
That mean no any balance, neither power balance nor performance balance
will be done on this cpu.

Above logical will be implemented by incoming patches.

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: pull all tasks from source group

In power balance, we hope some sched groups are fully empty to save
CPU power of them. So, we want to move any tasks from them.

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: no balance for prefer_sibling in power scheduling

In power aware scheduling, we don't want to balance 'prefer_sibling'
groups just because local group has capacity.
If the local group has no tasks at the time, that is the power
balance hope so.

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: add new members of sd_lb_stats

Added 4 new members in sb_lb_stats, that will be used in incomming
power aware balance.

group_min; 	//least utliszation group in domain
min_load_per_task; //load_per_task in group_min
leader_util;	// sum utilizations of group_leader
min_util;	// sum utilizations of group_min

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: power aware load balance

This patch enabled the power aware consideration in load balance.

As mentioned in the power aware scheduler proposal, Power aware
scheduling has 2 assumptions:
1, race to idle is helpful for power saving
2, less active sched_groups will reduce power consumption

The first assumption make performance policy take over scheduling when
any scheduler group is busy.
The second assumption make power aware scheduling try to pack disperse
tasks into fewer groups.

The enabling logical summary here:
1, Collect power aware scheduler statistics during performance load
balance statistics collection.
2, If the balance cpu is eligible for power load balance, just do it
and forget performance load balance. If the domain is suitable for
power balance, but the cpu is inappropriate(idle or full), stop both
power/performance balance in this domain. If using performance balance
or any group is busy, do performance balance.

Above logical is mainly implemented in update_sd_lb_power_stats(). It
decides if a domain is suitable for power aware scheduling. If so,
it will fill the dst group and source group accordingly.

This patch reused some of Suresh's power saving load balance code.

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: lazy power balance

When active task number in sched domain waves around the power friendly
scheduling creteria, scheduling will thresh between the power friendly
balance and performance balance, bring unnecessary task migration.
The typical benchmark is 'make -j x'.

To remove such issue, introduce a u64 perf_lb_record variable to record
performance load balance history. If there is no performance LB for
continuing 32 times load balancing, or no LB for 8 times max_interval ms,
or only 4 times performance LB in last 64 times load balancing, then we
accept a power friendly LB. Otherwise, give up this time power friendly
LB chance, do nothing.

With this patch, the worst case for power scheduling -- kbuild, gets
similar performance/watts value among different policy.

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: don't do power balance on share cpu power domain

Packing tasks among such domain can't save power, just performance
losing. So no power balance on them.

Signed-off-by: Alex Shi <alex.shi@intel.com>
sched: make sure select_tas_rq_fair get a cpu

Problem:

select_task_rq_fair() returns a target CPU/ waking CPU if no balancing is
required. However with the current power aware scheduling in this path, an
invalid CPU might be returned.

If get_cpu_for_power_policy() fails to find a new_cpu for the forked task,
then there is a possibility that the new_cpu could continue to be -1, till
the end of the select_task_rq_fair() if the search for a new cpu ahead in
this function also fails. Since this scenario is unexpected by
the callers of  select_task_rq_fair(),this needs to be fixed.

Fix:

Do not intermix the variables meant to reflect the target CPU of power save
and performance policies. If the target CPU of powersave is successful in being
found, return it. Else allow the performance policy to take a call on the
target CPU.

The above scenario was caught when a kernel crash resulted with a bad data access
interrupt, during a kernbench run on a 2 socket,16 core machine,with each core
having SMT-4

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Alex Shi <alex.shi@intel.com>