cpufreq: interactive: New 'interactive' governor
authorMike Chan <mike@android.com>
Tue, 22 Jun 2010 18:26:45 +0000 (11:26 -0700)
committerDan Willemsen <dwillemsen@nvidia.com>
Thu, 1 Dec 2011 05:38:25 +0000 (21:38 -0800)
commitd85bd86bd9db50e3f9a3ac568756c53ce6453c6a
tree7994bbd259f71dbcaac7a39f16ff02dd74cb0c2e
parenteb283c5eee37992538eddc2ef25ab6fdf7114a19
cpufreq: interactive: New 'interactive' governor

This governor is designed for latency-sensitive workloads, such as
interactive user interfaces.  The interactive governor aims to be
significantly more responsive to ramp CPU quickly up when CPU-intensive
activity begins.

Existing governors sample CPU load at a particular rate, typically
every X ms.  This can lead to under-powering UI threads for the period of
time during which the user begins interacting with a previously-idle system
until the next sample period happens.

The 'interactive' governor uses a different approach. Instead of sampling
the CPU at a specified rate, the governor will check whether to scale the
CPU frequency up soon after coming out of idle.  When the CPU comes out of
idle, a timer is configured to fire within 1-2 ticks.  If the CPU is very
busy from exiting idle to when the timer fires then we assume the CPU is
underpowered and ramp to MAX speed.

If the CPU was not sufficiently busy to immediately ramp to MAX speed, then
the governor evaluates the CPU load since the last speed adjustment,
choosing the highest value between that longer-term load or the short-term
load since idle exit to determine the CPU speed to ramp to.

A realtime thread is used for scaling up, giving the remaining tasks the
CPU performance benefit, unlike existing governors which are more likely to
schedule rampup work to occur after your performance starved tasks have
completed.

The tuneables for this governor are:
/sys/devices/system/cpu/cpufreq/interactive/min_sample_time:
The minimum amount of time to spend at the current frequency before
ramping down. This is to ensure that the governor has seen enough
historic CPU load data to determine the appropriate workload.
Default is 80000 uS.
/sys/devices/system/cpu/cpufreq/interactive/go_maxspeed_load
The CPU load at which to ramp to max speed.  Default is 85.

Change-Id: Ib2b362607c62f7c56d35f44a9ef3280f98c17585
Signed-off-by: Mike Chan <mike@android.com>
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Bug: 3152864
Documentation/cpu-freq/governors.txt
drivers/cpufreq/Kconfig
drivers/cpufreq/Makefile
drivers/cpufreq/cpufreq_interactive.c [new file with mode: 0644]
include/linux/cpufreq.h