[PATCH 37/70] cpufreq: interactive: default go_hispeed_load 99%, doc updates

["Bálint Czobor" <czoborbalint@gmail.com>]

From: Todd Poynor <toddpoynor@google.com>

Update default go_hispeed_load from 85% to 99%.  Recent changes to the
governor now use a default target_load of 90%.  go_hispeed_load should
not be lower than the target load for hispeed_freq, which could lead
to oscillating speed decisions.  Other recent changes reduce the need
to dampen speed jumps on load spikes, while input event boosts from
userspace are the preferred method for anticipating load spikes with
UI impacts.

General update to the documentation to reflect recent changes.

Change-Id: I1b92f3091f42c04b10503cd1169a943b5dfd6faf
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Bálint Czobor <czoborbalint@gmail.com>
---
 Documentation/cpu-freq/governors.txt  |   64 ++++++++++++++++-----------------
 drivers/cpufreq/cpufreq_interactive.c |    2 +-
 2 files changed, 33 insertions(+), 33 deletions(-)

diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt
index b15f6d2..4d8ae34 100644
--- a/Documentation/cpu-freq/governors.txt
+++ b/Documentation/cpu-freq/governors.txt
@@ -224,23 +224,8 @@ sampling rate.
 
 The CPUfreq governor "interactive" is designed for latency-sensitive,
 interactive workloads. This governor sets the CPU speed depending on
-usage, similar to "ondemand" and "conservative" governors.  However,
-the governor is more aggressive about scaling the CPU speed up in
-response to CPU-intensive activity.
-
-Sampling the CPU load every X ms can lead to under-powering the CPU
-for X ms, leading to dropped frames, stuttering UI, etc.  Instead of
-sampling the cpu at a specified rate, the interactive 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 between exiting idle and
-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 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.
+usage, similar to "ondemand" and "conservative" governors, but with a
+different set of configurable behaviors.
 
 The tuneable values for this governor are:
 
@@ -262,36 +247,51 @@ values also usually appear in an ascending order. The default is
 target load 90% for all speeds.
 
 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.
+frequency before ramping down. Default is 80000 uS.
 
 hispeed_freq: An intermediate "hi speed" at which to initially ramp
 when CPU load hits the value specified in go_hispeed_load.  If load
 stays high for the amount of time specified in above_hispeed_delay,
-then speed may be bumped higher.  Default is maximum speed.
+then speed may be bumped higher.  Default is the maximum speed
+allowed by the policy at governor initialization time.
 
-go_hispeed_load: The CPU load at which to ramp to the intermediate "hi
-speed".  Default is 85%.
+go_hispeed_load: The CPU load at which to ramp to hispeed_freq.
+Default is 99%.
 
-above_hispeed_delay: Once speed is set to hispeed_freq, wait for this
-long before bumping speed higher in response to continued high load.
+above_hispeed_delay: When speed is at or above hispeed_freq, wait for
+this long before raising speed in response to continued high load.
 Default is 20000 uS.
 
-timer_rate: Sample rate for reevaluating cpu load when the system is
-not idle.  Default is 20000 uS.
-
-input_boost: If non-zero, boost speed of all CPUs to hispeed_freq on
-touchscreen activity.  Default is 0.
+timer_rate: Sample rate for reevaluating CPU load when the CPU is not
+idle.  A deferrable timer is used, such that the CPU will not be woken
+from idle to service this timer until something else needs to run.
+(The maximum time to allow deferring this timer when not running at
+minimum speed is configurable via timer_slack.)  Default is 20000 uS.
+
+timer_slack: Maximum additional time to defer handling the governor
+sampling timer beyond timer_rate when running at speeds above the
+minimum.  For platforms that consume additional power at idle when
+CPUs are running at speeds greater than minimum, this places an upper
+bound on how long the timer will be deferred prior to re-evaluating
+load and dropping speed.  For example, if timer_rate is 20000uS and
+timer_slack is 10000uS then timers will be deferred for up to 30msec
+when not at lowest speed.  A value of -1 means defer timers
+indefinitely at all speeds.  Default is 80000 uS.
 
 boost: If non-zero, immediately boost speed of all CPUs to at least
 hispeed_freq until zero is written to this attribute.  If zero, allow
 CPU speeds to drop below hispeed_freq according to load as usual.
+Default is zero.
 
-boostpulse: Immediately boost speed of all CPUs to hispeed_freq for
-min_sample_time, after which speeds are allowed to drop below
+boostpulse: On each write, immediately boost speed of all CPUs to
+hispeed_freq for at least the period of time specified by
+boostpulse_duration, after which speeds are allowed to drop below
 hispeed_freq according to load as usual.
 
+boostpulse_duration: Length of time to hold CPU speed at hispeed_freq
+on a write to boostpulse, before allowing speed to drop according to
+load as usual.  Default is 80000 uS.
+
 
 3. The Governor Interface in the CPUfreq Core
 =============================================
diff --git a/drivers/cpufreq/cpufreq_interactive.c b/drivers/cpufreq/cpufreq_interactive.c
index d22d162..fdc2a47 100644
--- a/drivers/cpufreq/cpufreq_interactive.c
+++ b/drivers/cpufreq/cpufreq_interactive.c
@@ -66,7 +66,7 @@ static spinlock_t speedchange_cpumask_lock;
 static unsigned int hispeed_freq;
 
 /* Go to hi speed when CPU load at or above this value. */
-#define DEFAULT_GO_HISPEED_LOAD 85
+#define DEFAULT_GO_HISPEED_LOAD 99
 static unsigned long go_hispeed_load;
 
 /* Target load.  Lower values result in higher CPU speeds. */
-- 
1.7.9.5