lib: add generic strnlen_user() function

This adds a new generic optimized strnlen_user() function that uses the
<asm/word-at-a-time.h> infrastructure to portably do efficient string
handling.

In many ways, strnlen is much simpler than strncpy, and in particular we
can always pre-align the words we load from memory.  That means that all
the worries about alignment etc are a non-issue, so this one can easily
be used on any architecture.  You obviously do have to do the
appropriate word-at-a-time.h macros.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Paul Reioux <reioux@gmail.com>
ARM: use generic strnlen_user and strncpy_from_user functions

This patch implements the word-at-a-time interface for ARM using the
same algorithm as x86. We use the fls macro from ARMv5 onwards, where
we have a clz instruction available which saves us a mov instruction
when targetting Thumb-2. For older CPUs, we use the magic 0x0ff0001
constant. Big-endian configurations make use of the implementation from
asm-generic.

With this implemented, we can replace our byte-at-a-time strnlen_user
and strncpy_from_user functions with the optimised generic versions.

Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
modified for Mako from LKML reference

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

Conflicts:

	arch/arm/lib/Makefile
sched: Optimize build_sched_domains() for saving first SD node for a cpu

Date	Tue, 4 Jun 2013 16:50:18 +0530

We are saving first scheduling domain for a cpu in build_sched_domains() by
iterating over the nested sd->child list. We don't actually need to do it this
way.

*per_cpu_ptr(d.sd, i) is guaranteed to be NULL in the beginning as we have
called __visit_domain_allocation_hell() which does a memset to zero for struct
s_data.

So, save pointer to first SD while running the iteration loop over tl's.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: Optimize build_sched_domains() for saving first SD node for a cpu

We are saving first scheduling domain for a cpu in build_sched_domains() by
iterating over the nested sd->child list. We don't actually need to do it this
way.

tl will be equal to sched_domain_topology for the first iteration and so we can
set *per_cpu_ptr(d.sd, i) based on that.  So, save pointer to first SD while
running the iteration loop over tl's.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: Remove unused params of build_sched_domain()

Date	Tue, 4 Jun 2013 16:50:19 +0530

build_sched_domain() never uses parameter struct s_data *d and so passing it is
useless.

Remove it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: Use cached value of span instead of calling sched_domain_span()

Date	Tue, 11 Jun 2013 16:32:43 +0530

In the beginning of build_sched_groups() we called sched_domain_span() and
cached its return value in span. Few statements later we are calling it again to
get the same pointer.

Lets use the cached value instead as it hasn't changed in between.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: don't call get_group() for covered cpus

Date	Tue, 11 Jun 2013 16:32:44 +0530

In build_sched_groups() we don't need to call get_group() for cpus which are
already covered in previous iterations. So, call get_group() after checking if
cpu is covered or not.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: remove WARN_ON(!sd) from init_sched_groups_power()

Date	Tue, 11 Jun 2013 16:32:45 +0530

sd can't be NULL in init_sched_groups_power() and so checking it for NULL isn't
useful. In case it is required, then also we need to rearrange the code a bit as
we already accessed invalid pointer sd to get sg: sg = sd->groups.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Paul Reioux <reioux@gmail.com>
sched: Reduce overestimating rq->avg_idle

Date	Thu, 29 Aug 2013 13:05:34 -0700

When updating avg_idle, if the delta exceeds some max value, then avg_idle
gets set to the max, regardless of what the previous avg was. This can cause
avg_idle to often be overestimated.

This patch modifies the way we update avg_idle by always updating it with the
function call to update_avg() first. Then, if avg_idle exceeds the max, we set
it to the max.

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Rik van Riel <riel@redhat.com>

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: remove redundant update_runtime notifier

migration_call() will do all the things that update_runtime() does.
So it seems update_runtime() is a redundant notifier, remove it.

Furthermore, there is potential risk that the current code will catch
BUG_ON at line 687 of rt.c when do cpu hotplug while there are realtime
threads running because of enable runtime twice.

Change-Id: I0fdad8d5a1cebb845d3f308b205dbd6517c3e4de
Cc: bitbucket@online.de
Signed-off-by: Neil Zhang <zhangwm@marvell.com>
Reviewed-on: http://git-master/r/215596
(cherry picked from commit 8f646de983f24361814d9a6ca679845fb2265807)
Reviewed-on: http://git-master/r/223067
Reviewed-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
Tested-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
Reviewed-by: Paul Walmsley <pwalmsley@nvidia.com>
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Diwakar Tundlam <dtundlam@nvidia.com>
sched: reinitialize rq->next_balance when a CPU is hot-added

Reinitialize rq->next_balance when a CPU is hot-added.  Otherwise,
scheduler domain rebalancing may be skipped if rq->next_balance was
set to a future time when the CPU was last active, and the
newly-re-added CPU is in idle_balance().  As a result, the
newly-re-added CPU will remain idle with no tasks scheduled until the
softlockup watchdog runs - potentially 4 seconds later.  This can
waste energy and reduce performance.

This behavior can be observed in some SoC kernels, which use CPU
hotplug to dynamically remove and add CPUs in response to load.  In
one case that triggered this behavior,

0. the system started with all cores enabled, running multi-threaded
   CPU-bound code;

1. the system entered some single-threaded code;

2. a CPU went idle and was hot-removed;

3. the system started executing a multi-threaded CPU-bound task;

4. the CPU from event 2 was re-added, to respond to the load.

The time interval between events 2 and 4 was approximately 300
milliseconds.

Of course, ideally CPU hotplug would not be used in this manner,
but this patch does appear to fix a real bug.

Nvidia folks: this patch is submitted as at least a partial fix for
bug 1243368 ("[sched] Load-balancing not happening correctly after
cores brought online")

Change-Id: Iabac21e110402bb581b7db40c42babc951d378d0
Signed-off-by: Paul Walmsley <pwalmsley@nvidia.com>
Cc: Peter Boonstoppel <pboonstoppel@nvidia.com>
Reviewed-on: http://git-master/r/208927
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Peter Zu <pzu@nvidia.com>
Reviewed-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
GVS: Gerrit_Virtual_Submit
Tested-by: Peter Zu <pzu@nvidia.com>
Reviewed-by: Yu-Huan Hsu <yhsu@nvidia.com>
sched/cpuidle: reduce IPI storm. Backport upstream 3.16 scheduler updates

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

Conflicts:
	kernel/sched/core.c
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: 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>
sched: change cpu_avg_load_per_task using h_nr_running

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

Since cpu_avg_load_per_task is used only by cfs scheduler, its meaning
should present the average cfs type task load in the current run queue.
Thus we change it to h_nr_running for well presenting its meaning.

Signed-off-by: Lei Wen <leiwen@marvell.com>
Signed-off-by: Paul Reioux <reioux@gmail.com>