sched/nohz: Fix rq->cpu_load[] calculations

While investigating why the load-balancer did funny I found that the
rq->cpu_load[] tables were completely screwy.. a bit more digging
revealed that the updates that got through were missing ticks followed
by a catchup of 2 ticks.

The catchup assumes the cpu was idle during that time (since only nohz
can cause missed ticks and the machine is idle etc..) this means that
esp. the higher indices were significantly lower than they ought to
be.

The reason for this is that its not correct to compare against jiffies
on every jiffy on any other cpu than the cpu that updates jiffies.

This patch cludges around it by only doing the catch-up stuff from
nohz_idle_balance() and doing the regular stuff unconditionally from
the tick.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: pjt@google.com
Cc: Venkatesh Pallipadi <venki@google.com>
Link: http://lkml.kernel.org/n/tip-tp4kj18xdd5aj4vvj0qg55s2@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
modified for Linux 3.0 from Linux 3.4+ by faux123
sched/fair: Improve the ->group_imb logic

Group imbalance is meant to deal with situations where affinity masks
and sched domains don't align well, such as 3 cpus from one group and
6 from another. In this case the domain based balancer will want to
put an equal amount of tasks on each side even though they don't have
equal cpus.

Currently group_imb is set whenever two cpus of a group have a weight
difference of at least one avg task and the heaviest cpu has at least
two tasks. A group with imbalance set will always be picked as busiest
and a balance pass will be forced.
The problem is that even if there are no affinity masks this stuff can
trigger and cause weird balancing decisions, eg. the observed
behaviour was that of 6 cpus, 5 had 2 and 1 had 3 tasks, due to the
difference of 1 avg load (they all had the same weight) and nr_running
being >1 the group_imbalance logic triggered and did the weird thing
of pulling more load instead of trying to move the 1 excess task to
the other domain of 6 cpus that had 5 cpu with 2 tasks and 1 cpu with
1 task.
Curb the group_imbalance stuff by making the nr_running condition
weaker by also tracking the min_nr_running and using the difference in
nr_running over the set instead of the absolute max nr_running.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-9s7dedozxo8kjsb9kqlrukkf@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
modified for Linux 3.0 from Linux 3.4+ by faux123
sched: Folding nohz load accounting more accurate

After patch 453494c3d4 (sched: Fix nohz load accounting -- again!), we can fold
the idle into calc_load_tasks_idle between the last cpu load calculating and
calc_global_load calling. However problem still exits between the first cpu
load calculating and the last cpu load calculating. Every time when we do load
calculating, calc_load_tasks_idle will be added into calc_load_tasks, even if
the idle load is caused by calculated cpus. This problem is also described in
the following link:

https://lkml.org/lkml/2012/5/24/419

This bug can be found in our work load. The average running processes number
is about 15, but the load only shows about 4.

The patch provides a solution, by taking calculated load cpus' idle away from
 real effective idle. First adds a cpumask to record those cpus that alread
calculated their load, and then adds a calc_unmask_cpu_load_idle to record
thoses not marked cpus' go-idle load. Calc_unmask_cpu_load_idle takes place
of calc_load_tasks_idle to be added into calc_load_tasks every 5HZ when cpu
calculate its load. Go-idle load on those cpus which load alread has been calculated
will only be added into calc_load_tasks_idle, no in calc_unmask_cpu_load_idle.

Reported-by: Sha Zhengju <handai.szj@xxxxxxxxx>
Signed-off-by: Charles Wang <muming.wq@xxxxxxxxxx>
modified for HTC One X kernel from Linux 3.4+ by faux123
sched: clock wrap bug in 2.6.35-stable kills scheduling

On Mon, 2012-06-25 at 11:45 +0200, Peter Zijlstra wrote:
> On Sun, 2012-06-24 at 19:32 +0200, Thomas Lange wrote:
> > Bug was introduced in 2.6.35.12 and is still present in linux-2.6.35.y HEAD.
>
> Ok, so nobody cares about that.. what does something recent like 3.5-rc4
> do?
>
> If that's fixed, find the patch that fixes it. If not, we'll have a
> look.

If anything, I think something like the below ought to cure things.
sched: don't call task_group() many times in set_task_rq()

It improves perfomance, especially if autogroup enabled.

The size of set_task_rq() was 0x180 and now it is 0xa0.

Signed-off-by: Andrew Vagin <avagin@openvz.org>