android_kernel_oneplus_msm8998/Documentation/cpu-freq/governors.txt

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CPU frequency and voltage scaling code in the Linux(TM) kernel
L i n u x C P U F r e q
C P U F r e q G o v e r n o r s
- information for users and developers -
Dominik Brodowski <linux@brodo.de>
some additions and corrections by Nico Golde <nico@ngolde.de>
Clock scaling allows you to change the clock speed of the CPUs on the
fly. This is a nice method to save battery power, because the lower
the clock speed, the less power the CPU consumes.
Contents:
---------
1. What is a CPUFreq Governor?
2. Governors In the Linux Kernel
2.1 Performance
2.2 Powersave
2.3 Userspace
2.4 Ondemand
2.5 Conservative
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
2010-06-22 11:26:45 -07:00
2.6 Interactive
3. The Governor Interface in the CPUfreq Core
1. What Is A CPUFreq Governor?
==============================
Most cpufreq drivers (except the intel_pstate and longrun) or even most
cpu frequency scaling algorithms only offer the CPU to be set to one
frequency. In order to offer dynamic frequency scaling, the cpufreq
core must be able to tell these drivers of a "target frequency". So
cpufreq: Implement light weight ->target_index() routine Currently, the prototype of cpufreq_drivers target routines is: int target(struct cpufreq_policy *policy, unsigned int target_freq, unsigned int relation); And most of the drivers call cpufreq_frequency_table_target() to get a valid index of their frequency table which is closest to the target_freq. And they don't use target_freq and relation after that. So, it makes sense to just do this work in cpufreq core before calling cpufreq_frequency_table_target() and simply pass index instead. But this can be done only with drivers which expose their frequency table with cpufreq core. For others we need to stick with the old prototype of target() until those drivers are converted to expose frequency tables. This patch implements the new light weight prototype for target_index() routine. It looks like this: int target_index(struct cpufreq_policy *policy, unsigned int index); CPUFreq core will call cpufreq_frequency_table_target() before calling this routine and pass index to it. Because CPUFreq core now requires to call routines present in freq_table.c CONFIG_CPU_FREQ_TABLE must be enabled all the time. This also marks target() interface as deprecated. So, that new drivers avoid using it. And Documentation is updated accordingly. It also converts existing .target() to newly defined light weight .target_index() routine for many driver. Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no> Acked-by: Jesper Nilsson <jesper.nilsson@axis.com> Acked-by: Linus Walleij <linus.walleij@linaro.org> Acked-by: Russell King <linux@arm.linux.org.uk> Acked-by: David S. Miller <davem@davemloft.net> Tested-by: Andrew Lunn <andrew@lunn.ch> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rjw@rjwysocki.net>
2013-10-25 19:45:48 +05:30
these specific drivers will be transformed to offer a "->target/target_index"
call instead of the existing "->setpolicy" call. For "longrun", all
stays the same, though.
How to decide what frequency within the CPUfreq policy should be used?
That's done using "cpufreq governors". Two are already in this patch
-- they're the already existing "powersave" and "performance" which
set the frequency statically to the lowest or highest frequency,
respectively. At least two more such governors will be ready for
addition in the near future, but likely many more as there are various
different theories and models about dynamic frequency scaling
around. Using such a generic interface as cpufreq offers to scaling
governors, these can be tested extensively, and the best one can be
selected for each specific use.
Basically, it's the following flow graph:
CPU can be set to switch independently | CPU can only be set
within specific "limits" | to specific frequencies
"CPUfreq policy"
consists of frequency limits (policy->{min,max})
and CPUfreq governor to be used
/ \
/ \
/ the cpufreq governor decides
/ (dynamically or statically)
/ what target_freq to set within
/ the limits of policy->{min,max}
/ \
/ \
cpufreq: Implement light weight ->target_index() routine Currently, the prototype of cpufreq_drivers target routines is: int target(struct cpufreq_policy *policy, unsigned int target_freq, unsigned int relation); And most of the drivers call cpufreq_frequency_table_target() to get a valid index of their frequency table which is closest to the target_freq. And they don't use target_freq and relation after that. So, it makes sense to just do this work in cpufreq core before calling cpufreq_frequency_table_target() and simply pass index instead. But this can be done only with drivers which expose their frequency table with cpufreq core. For others we need to stick with the old prototype of target() until those drivers are converted to expose frequency tables. This patch implements the new light weight prototype for target_index() routine. It looks like this: int target_index(struct cpufreq_policy *policy, unsigned int index); CPUFreq core will call cpufreq_frequency_table_target() before calling this routine and pass index to it. Because CPUFreq core now requires to call routines present in freq_table.c CONFIG_CPU_FREQ_TABLE must be enabled all the time. This also marks target() interface as deprecated. So, that new drivers avoid using it. And Documentation is updated accordingly. It also converts existing .target() to newly defined light weight .target_index() routine for many driver. Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no> Acked-by: Jesper Nilsson <jesper.nilsson@axis.com> Acked-by: Linus Walleij <linus.walleij@linaro.org> Acked-by: Russell King <linux@arm.linux.org.uk> Acked-by: David S. Miller <davem@davemloft.net> Tested-by: Andrew Lunn <andrew@lunn.ch> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rjw@rjwysocki.net>
2013-10-25 19:45:48 +05:30
Using the ->setpolicy call, Using the ->target/target_index call,
the limits and the the frequency closest
"policy" is set. to target_freq is set.
It is assured that it
is within policy->{min,max}
2. Governors In the Linux Kernel
================================
2.1 Performance
---------------
The CPUfreq governor "performance" sets the CPU statically to the
highest frequency within the borders of scaling_min_freq and
scaling_max_freq.
2.2 Powersave
-------------
The CPUfreq governor "powersave" sets the CPU statically to the
lowest frequency within the borders of scaling_min_freq and
scaling_max_freq.
2.3 Userspace
-------------
The CPUfreq governor "userspace" allows the user, or any userspace
program running with UID "root", to set the CPU to a specific frequency
by making a sysfs file "scaling_setspeed" available in the CPU-device
directory.
2.4 Ondemand
------------
The CPUfreq governor "ondemand" sets the CPU depending on the
current usage. To do this the CPU must have the capability to
switch the frequency very quickly. There are a number of sysfs file
accessible parameters:
sampling_rate: measured in uS (10^-6 seconds), this is how often you
want the kernel to look at the CPU usage and to make decisions on
what to do about the frequency. Typically this is set to values of
around '10000' or more. It's default value is (cmp. with users-guide.txt):
transition_latency * 1000
Be aware that transition latency is in ns and sampling_rate is in us, so you
get the same sysfs value by default.
Sampling rate should always get adjusted considering the transition latency
To set the sampling rate 750 times as high as the transition latency
in the bash (as said, 1000 is default), do:
echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \
>ondemand/sampling_rate
sampling_rate_min:
The sampling rate is limited by the HW transition latency:
transition_latency * 100
Or by kernel restrictions:
nohz: Rename CONFIG_NO_HZ to CONFIG_NO_HZ_COMMON We are planning to convert the dynticks Kconfig options layout into a choice menu. The user must be able to easily pick any of the following implementations: constant periodic tick, idle dynticks, full dynticks. As this implies a mutual exclusion, the two dynticks implementions need to converge on the selection of a common Kconfig option in order to ease the sharing of a common infrastructure. It would thus seem pretty natural to reuse CONFIG_NO_HZ to that end. It already implements all the idle dynticks code and the full dynticks depends on all that code for now. So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ. On the other hand we want to stay backward compatible: if CONFIG_NO_HZ is set in an older config file, we want to enable CONFIG_NO_HZ_IDLE by default. But we can't afford both at the same time or we run into a circular dependency: 1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select CONFIG_NO_HZ 2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLE We might be able to support that from Kconfig/Kbuild but it may not be wise to introduce such a confusing behaviour. So to solve this, create a new CONFIG_NO_HZ_COMMON option which gathers the common code between idle and full dynticks (that common code for now is simply the idle dynticks code) and select it from their referring Kconfig. Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ to it for backward compatibility. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@linaro.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Namhyung Kim <namhyung.kim@lge.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
2011-08-10 23:21:01 +02:00
If CONFIG_NO_HZ_COMMON is set, the limit is 10ms fixed.
If CONFIG_NO_HZ_COMMON is not set or nohz=off boot parameter is used, the
limits depend on the CONFIG_HZ option:
HZ=1000: min=20000us (20ms)
HZ=250: min=80000us (80ms)
HZ=100: min=200000us (200ms)
The highest value of kernel and HW latency restrictions is shown and
used as the minimum sampling rate.
up_threshold: defines what the average CPU usage between the samplings
of 'sampling_rate' needs to be for the kernel to make a decision on
whether it should increase the frequency. For example when it is set
to its default value of '95' it means that between the checking
intervals the CPU needs to be on average more than 95% in use to then
decide that the CPU frequency needs to be increased.
ignore_nice_load: this parameter takes a value of '0' or '1'. When
set to '0' (its default), all processes are counted towards the
'cpu utilisation' value. When set to '1', the processes that are
run with a 'nice' value will not count (and thus be ignored) in the
overall usage calculation. This is useful if you are running a CPU
intensive calculation on your laptop that you do not care how long it
takes to complete as you can 'nice' it and prevent it from taking part
in the deciding process of whether to increase your CPU frequency.
sampling_down_factor: this parameter controls the rate at which the
kernel makes a decision on when to decrease the frequency while running
at top speed. When set to 1 (the default) decisions to reevaluate load
are made at the same interval regardless of current clock speed. But
when set to greater than 1 (e.g. 100) it acts as a multiplier for the
scheduling interval for reevaluating load when the CPU is at its top
speed due to high load. This improves performance by reducing the overhead
of load evaluation and helping the CPU stay at its top speed when truly
busy, rather than shifting back and forth in speed. This tunable has no
effect on behavior at lower speeds/lower CPU loads.
powersave_bias: this parameter takes a value between 0 to 1000. It
defines the percentage (times 10) value of the target frequency that
will be shaved off of the target. For example, when set to 100 -- 10%,
when ondemand governor would have targeted 1000 MHz, it will target
1000 MHz - (10% of 1000 MHz) = 900 MHz instead. This is set to 0
(disabled) by default.
When AMD frequency sensitivity powersave bias driver --
drivers/cpufreq/amd_freq_sensitivity.c is loaded, this parameter
defines the workload frequency sensitivity threshold in which a lower
frequency is chosen instead of ondemand governor's original target.
The frequency sensitivity is a hardware reported (on AMD Family 16h
Processors and above) value between 0 to 100% that tells software how
the performance of the workload running on a CPU will change when
frequency changes. A workload with sensitivity of 0% (memory/IO-bound)
will not perform any better on higher core frequency, whereas a
workload with sensitivity of 100% (CPU-bound) will perform better
higher the frequency. When the driver is loaded, this is set to 400
by default -- for CPUs running workloads with sensitivity value below
40%, a lower frequency is chosen. Unloading the driver or writing 0
will disable this feature.
2.5 Conservative
----------------
The CPUfreq governor "conservative", much like the "ondemand"
governor, sets the CPU depending on the current usage. It differs in
behaviour in that it gracefully increases and decreases the CPU speed
rather than jumping to max speed the moment there is any load on the
CPU. This behaviour more suitable in a battery powered environment.
The governor is tweaked in the same manner as the "ondemand" governor
through sysfs with the addition of:
freq_step: this describes what percentage steps the cpu freq should be
increased and decreased smoothly by. By default the cpu frequency will
increase in 5% chunks of your maximum cpu frequency. You can change this
value to anywhere between 0 and 100 where '0' will effectively lock your
CPU at a speed regardless of its load whilst '100' will, in theory, make
it behave identically to the "ondemand" governor.
down_threshold: same as the 'up_threshold' found for the "ondemand"
governor but for the opposite direction. For example when set to its
default value of '20' it means that if the CPU usage needs to be below
20% between samples to have the frequency decreased.
sampling_down_factor: similar functionality as in "ondemand" governor.
But in "conservative", it controls the rate at which the kernel makes
a decision on when to decrease the frequency while running in any
speed. Load for frequency increase is still evaluated every
sampling rate.
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
2010-06-22 11:26:45 -07:00
2.6 Interactive
---------------
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, but with a
different set of configurable behaviors.
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
2010-06-22 11:26:45 -07:00
The tuneable values for this governor are:
target_loads: CPU load values used to adjust speed to influence the
current CPU load toward that value. In general, the lower the target
load, the more often the governor will raise CPU speeds to bring load
below the target. The format is a single target load, optionally
followed by pairs of CPU speeds and CPU loads to target at or above
those speeds. Colons can be used between the speeds and associated
target loads for readability. For example:
85 1000000:90 1700000:99
targets CPU load 85% below speed 1GHz, 90% at or above 1GHz, until
1.7GHz and above, at which load 99% is targeted. If speeds are
specified these must appear in ascending order. Higher target load
values are typically specified for higher speeds, that is, target load
values also usually appear in an ascending order. The default is
target load 90% for all speeds.
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
2010-06-22 11:26:45 -07:00
min_sample_time: The minimum amount of time to spend at the current
frequency before ramping down. Default is 80000 uS.
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
2010-06-22 11:26:45 -07:00
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 the maximum speed
allowed by the policy at governor initialization time.
go_hispeed_load: The CPU load at which to ramp to hispeed_freq.
Default is 99%.
above_hispeed_delay: When speed is at or above hispeed_freq, wait for
this long before raising speed in response to continued high load.
The format is a single delay value, optionally followed by pairs of
CPU speeds and the delay to use at or above those speeds. Colons can
be used between the speeds and associated delays for readability. For
example:
80000 1300000:200000 1500000:40000
uses delay 80000 uS until CPU speed 1.3 GHz, at which speed delay
200000 uS is used until speed 1.5 GHz, at which speed (and above)
delay 40000 uS is used. If speeds are specified these must appear in
ascending order. Default is 20000 uS.
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
2010-06-22 11:26:45 -07:00
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: 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.
align_windows: If non-zero, align governor timer window to fire at
multiples of number of jiffies timer_rate converts to.
use_sched_load: If non-zero, query scheduler for CPU busy time,
instead of collecting it directly in governor. This would allow
scheduler to adjust the busy time of each CPU to account for known
information such as migration. If non-zero, this also implies governor
sampling windows are aligned across CPUs, with same timer_rate,
regardless what align_windows is set to. Default is zero.
use_migration_notif: If non-zero, schedule hrtimer to fire in 1ms
to reevaluate frequency of notified CPU, unless the hrtimer is already
pending. If zero, ignore scheduler notification. Default is zero.
max_freq_hysteresis: Each time freq evaluation chooses policy->max,
next max_freq_hysteresis is considered as hysteresis period. During
this period, frequency target will not drop below hispeed_freq, no
matter how light actual workload is. If CPU load of any sampling
window exceeds go_hispeed_load during this period, governor will
directly increase frequency back to policy->max. Default is 0 uS.
ignore_hispeed_on_notif: If non-zero, do not apply hispeed related
logic if frequency evaluation is triggered by scheduler notification.
This includes ignoring go_hispeed_load, hispeed_freq in frequency
selection, and ignoring above_hispeed_delay that prevents frequency
ramp up. For evaluation triggered by timer, hispeed logic is still
always applied. ignore_hispeed_on_notif has no effect if
use_migration_notif is set to zero. Default is zero.
fast_ramp_down: If non-zero, do not apply min_sample_time if
frequency evaluation is triggered by scheduler notification. For
evaluation triggered by timer, min_sample_time is still always
enforced. fast_ramp_down has no effect if use_migration_notif is
set to zero. Default is zero.
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
2010-06-22 11:26:45 -07:00
enable_prediction: If non-zero, two frequencies will be calculated
during each sampling period: one based on busy time in previous sampling
period (f_prev), and the other based on prediction provided by scheduler
(f_pred). Max of both will be selected as final frequency. Hispeed
related logic, including both frequency selection and delay is ignored
if enable_prediction is set. If only f_pred but not f_prev picked
policy->max, max_freq_hysteresis period is not started/extended.
use_sched_load must be turned on before enabling this feature.
Default is zero.
3. The Governor Interface in the CPUfreq Core
=============================================
A new governor must register itself with the CPUfreq core using
"cpufreq_register_governor". The struct cpufreq_governor, which has to
be passed to that function, must contain the following values:
governor->name - A unique name for this governor
governor->governor - The governor callback function
governor->owner - .THIS_MODULE for the governor module (if
appropriate)
The governor->governor callback is called with the current (or to-be-set)
cpufreq_policy struct for that CPU, and an unsigned int event. The
following events are currently defined:
CPUFREQ_GOV_START: This governor shall start its duty for the CPU
policy->cpu
CPUFREQ_GOV_STOP: This governor shall end its duty for the CPU
policy->cpu
CPUFREQ_GOV_LIMITS: The limits for CPU policy->cpu have changed to
policy->min and policy->max.
If you need other "events" externally of your driver, _only_ use the
cpufreq_governor_l(unsigned int cpu, unsigned int event) call to the
CPUfreq core to ensure proper locking.
The CPUfreq governor may call the CPU processor driver using one of
these two functions:
int cpufreq_driver_target(struct cpufreq_policy *policy,
unsigned int target_freq,
unsigned int relation);
int __cpufreq_driver_target(struct cpufreq_policy *policy,
unsigned int target_freq,
unsigned int relation);
target_freq must be within policy->min and policy->max, of course.
What's the difference between these two functions? When your governor
still is in a direct code path of a call to governor->governor, the
per-CPU cpufreq lock is still held in the cpufreq core, and there's
no need to lock it again (in fact, this would cause a deadlock). So
use __cpufreq_driver_target only in these cases. In all other cases
(for example, when there's a "daemonized" function that wakes up
every second), use cpufreq_driver_target to lock the cpufreq per-CPU
lock before the command is passed to the cpufreq processor driver.