sched: reduce calculation effort in fix_small_imbalance

Date	Mon, 17 Jun 2013 21:00:22 +0800

Actually all below item could be repalced by scaled_busy_load_per_task
	(sds->busiest_load_per_task * SCHED_POWER_SCALE)
		/sds->busiest->sgp->power;

Signed-off-by: Lei Wen <leiwen@marvell.com>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: scale the busy and this queue's per-task load before compare

Date	Mon, 17 Jun 2013 21:00:23 +0800

Since for max_load and this_load, they are the value that already be
scaled. It is not reasonble to get a minimum value between the scaled
and non-scaled value, like below example.
	min(sds->busiest_load_per_task, sds->max_load);

Also add comment over in what condition, there would be cpu power gain
in move the load.

Signed-off-by: Lei Wen <leiwen@marvell.com>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: scale cpu load for judgment of group imbalance

Date	Mon, 17 Jun 2013 21:00:24 +0800

We cannot compare two load directly from two cpus, since the cpu power
over two cpu may vary largely.

Suppose we meet such two kind of cpus.
CPU A:
	No real time work, and there are 3 task, with rq->load.weight
being 512.
CPU B:
	Has real time work, and it take 3/4 of the cpu power, which
makes CFS only take 1/4, that is 1024/4=256 cpu power. And over its CFS
runqueue, there is only one task with weight as 128.

Since both cpu's CFS task take for half of the CFS's cpu power, it
should be considered as balanced in such case.

But original judgment like:
        if ((max_cpu_load - min_cpu_load) >= avg_load_per_task &&
            (max_nr_running - min_nr_running) > 1)
It makes (512-128)>=((512+128)/4), and lead to imbalance conclusion...
Make the load as scaled, to avoid such case.

Signed-off-by: Lei Wen <leiwen@marvell.com>

modified for Mako kernel from LKML reference
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: Consider max cost of idle balance per sched domain

Date    Thu, 29 Aug 2013 13:05:35 -0700

In this patch, we keep track of the max cost we spend doing idle load balancing
for each sched domain. If the avg time the CPU remains idle is less then the
time we have already spent on idle balancing + the max cost of idle balancing
in the sched domain, then we don't continue to attempt the balance. We also
keep a per rq variable, max_idle_balance_cost, which keeps track of the max
time spent on newidle load balances throughout all its domains. Additionally,
we swap sched_migration_cost used in idle_balance for rq->max_idle_balance_cost.

By using the max, we avoid overrunning the average. This further reduces the chance
we attempt balancing when the CPU is not idle for longer than the cost to balance.

I also limited the max cost of each domain to 5*sysctl_sched_migration_cost as
a way to prevent the max from becoming too inflated.

Signed-off-by: Jason Low <jason.low2@hp.com>

backported for Linux 3.4

Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: Periodically decay max cost of idle balance

This RFC patch builds on patch 2 and periodically decays that max value to
do idle balancing per sched domain.

Though we want to decay it fairly consistently, we may not want to lower it by
too much each time, especially since avg_idle is capped based on that value.
So I thought that decaying the value every second and lowering it by half a
percent each time appeared to be fairly reasonable.

This change would allow us to remove the limit we set on each domain's max cost
to idle balance. Also, since the max can be reduced now, we now have to
update rq->max_idle balance_cost more frequently. So after every idle balance,
we loop through the sched domain to find the max sd's newidle load balance cost
for any one domain. Then we will set rq->max_idle_balance_cost to that value.

Since we are now decaying the max cost to do idle balancing, that max cost can
also become not high enough. One possible explanation for why is that
besides the time spent on each newidle load balance, there are other costs
associated with attempting idle balancing. Idle balance also releases and
reacquires a spin lock. That cost is not counted when we keep track of each
domain's cost to do newidle load balance. Also, acquiring the rq locks can
potentially prevent other CPUs from running something useful. And after
migrating tasks, it might potentially have to pay the costs of cache misses and
refreshing tasks' cache.

Because of that, this patch also compares avg_idle with max cost to do idle
balancing + sched_migration_cost. While using the max cost helps reduce
overestimating the average idle, the sched_migration_cost can help account
for those additional costs of idle balancing.

Signed-off-by: Jason Low <jason.low2@hp.com>
[peterz: rewrote the logic, but kept the spirit]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
backported to Linux 3.4
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: change load balance number to h_nr_running of run queue

Date    Sun, 18 Aug 2013 16:25:15 +0800

Since rq->nr_running would include both migration and rt task, it is not
reasonable to seek to move nr_running number of task in the load_balance
function, since it only apply to cfs type.

Change it to cfs's h_nr_running, which could well present the task
number in current cfs queue.

Signed-off-by: Lei Wen <leiwen@marvell.com>
backported to Linux 3.4 by faux123
Signed-off-by: Paul Reioux <reioux@gmail.com>
kernel/sched/fair.c: fix merge derp

 from patch sched: change load balance number to h_nr_running of run queue

Signed-off-by: Paul Reioux <reioux@gmail.com>