cpufreq: Add cpu-boost driver

When certain bursty and important events take place, it might take a while
for the current cpufreq governor to notice the new load and react to it.
That would result in poor user experience. To alleviate this, the cpu-boost
driver boosts the frequency of a CPU for a short duration to maintain good
user experience while the governor catches up.

Specifically, this commit deals with ensuring that when "important" tasks
migrate from a fast CPU to a slow CPU, the frequency of the slow CPU is
boosted to be at least as high as the fast CPU for a short duration.

Since this driver enforces the boost by hooking into standard cpufreq
ADJUST notifiers, it has several advantages:
- More portable across kernel versions where the cpufreq internals might
  have been rewritten.
- Governor agnostic and hence works with multiple governors like
  conservative, ondemand, interactive, etc.
- Does not affect the sampling period/logic of existing governors.
- Can have the boost period adjusted independent of governor sampling
  period.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: Add a sync limit to cpu-boost

Perform frequency synchronization only when source CPU's frequency
is less than sync_threshold, else sync to the sync_threshold.

Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: Add Input Boost feature to the cpu-boost driver

On incoming input events boost the frequency of all online cpus
for at least input_boost_ms ms. This is accomplished by changing
the policy->min of all the online cpus to input_boost_freq.

Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: Disable cpu-boost by default

Disable cpu-boost by default, so that it can be turned ON only by
setting the module parameter boost_ms through command prompt when
required.

Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Fix queue_delayed_work_on() race with hotplug

Calling queue_delayed_work_on() on a CPU that's in the process of getting
hotplugged out can result in that CPU infinitely looping in
msm_pm_wait_cpu_shutdown(). If queue_delayed_work_on() is called after the
CPU is hotplugged out, it could wake up the CPU without going through the
hotplug path and cause instability. To avoid this, make sure the CPU is and
stays online while queuing a work on it.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Fix deadlock in wake_up of sync threads

If wake_up() is called on the current task on a CPU, the call will wait
until the current task is switched out before it wakes it up again and
returns.

The sync notifier for a CPU always runs on that CPU.

These two together can result in a deadlock if the sync notifier on CPU A
tries to wake up the sync thread of CPU A as it goes to sleep (is the
current task). A previous commit fixed this by adding a check to the sync
notifier to not wake up the sync thread of CPU A if it's the current task.

But this is still not sufficient to prevent deadlocks.

Sync thread of CPU A could be the current task on CPU B and sync thread of
CPU B could be the current task on CPU A.  At this point, if sync notifier
of CPU A and B try to wake up the sync threads of CPU A and B, it will
result in CPU A waiting for the current task in CPU B to get switched out
and CPU B waiting for the current task in CPU A to get switched out.  This
will result in a deadlock.

Prevent this scenario from happening by pinning the sync threads of each
CPU to run on that CPU. By doing this, we guarantee that sync notifiers
will only try to wake up sync threads running on that CPU. The fix added by
"cpufreq: cpu-boost: Resolve deadlock when waking up sync thread" ensures a
deadlock doesn't happen when a sync notifier tries to wake up a sync thread
running on that CPU.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Don't register for cpufreq notifiers too early

The cpufreq notifiers should be registered only after all the data
structures used in the notifier callbacks have been initialized. So, move
the cpufreq notifier registration to a later point in the init function.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Use interruptible wait to not affect load average

Using the function wait_event in cpu_boost puts the
process enter to 'D' state which contribute to the
high load average. This change will put the process
boost_sync in the 'S' state (interruptible sleep).

Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Use hotplug thread infrastructure

Before this patch, thread migration ran in uninterruptible threads.
Use the relatively new hotplug thread infrastructure with parked
threads to reduce cpu load (x4).

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Handle wakeup hints received for foreground tasks

A previous change modifies the notification conditions in the scheduler
to call the notifier chain even on foreground_thread wakeups for tasks
having load more than a threshold value.

If load_based_syncs is turned OFF then we do not need to perform
cpu boost for wakeup hints for foreground tasks from scheduler

Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Add unified hotplug and wake boost
cpufreq: cpu-boost: Export cpu boost status

* This will help hotplug drivers to know boost status
  of CPU and act accordingly.

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Export wakeup_boost

* This is needed to unify boost functions in cpu boost
  and hotplug drivers.

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: cpu-boost: Support separate input_boost_freq for
cpufreq: cpu-boost: Use one work to remove input boost for all CPUs

Currently each CPU queues up its own work for removing input boost.
This is not really required as boost removal for all the CPUs can
be done at the same time. So this patch uses a single work to
remove input boost for all the CPUs and updates the policy for
the online ones.

Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>