| Age | Commit message (Collapse) | Author | Files | Lines |
|---|
|
Notice that it is not necessary to assign tick_intercept_sum in every
iteration of the first loop over idle states in teo_select(), because
the intercept_sum value does not change after the assignment in a
given iteration of the loop, so its value after the last iteration of
the loop can be used for computing the tick_intercept_sum value
directly.
Modify the code accordingly.
No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Because the cost of calling tick_nohz_get_sleep_length() may increase
in the future, reorder the code in menu_select() so it first uses the
statistics to determine the expected idle duration. If that value is
higher than RESIDENCY_THRESHOLD_NS, tick_nohz_get_sleep_length() will
be called to obtain the time till the closest timer and refine the
idle duration prediction if necessary.
This causes the governor to always take the full overhead of
get_typical_interval() with the assumption that the cost will be
amortized by skipping the tick_nohz_get_sleep_length() call in the
cases when the predicted idle duration is relatively very small.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Doug Smythies <dsmythies@telus.net>
|
|
Currently, if the target residency of the deepest idle state is less than
the tick period length, which is quite likely for HZ=100, and the deepest
idle state is about to be selected by the TEO idle governor, the decision
on whether or not to stop the scheduler tick is based entirely on the
time till the closest timer. This is often insufficient, because timers
may not be in heavy use and there may be a plenty of other CPU wakeup
events between the deepest idle state's target residency and the closest
tick.
Allow the governor to count those events by making the deepest idle
state's bin effectively end at TICK_NSEC and introducing an additional
"bin" for collecting "hit" events (ie. the ones in which the measured
idle duration falls into the same bin as the time till the closest
timer) with idle duration values past TICK_NSEC.
This way the "intercepts" metric for the deepest idle state's bin
becomes nonzero in general, and so it can influence the decision on
whether or not to stop the tick possibly increasing the governor's
accuracy in that respect.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
Tested-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
|
|
Make teo_select() avoid calling tick_nohz_get_sleep_length() if the
candidate idle state to return is state 0 or if state 0 is a polling
one and the target residency of the current candidate one is below
a certain threshold, in which cases it may be assumed that the CPU will
be woken up immediately by a non-timer wakeup source and the timers
are not likely to matter.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
Tested-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
|
|
Because the cost of calling tick_nohz_get_sleep_length() may increase
in the future, reorder the code in teo_select() so it first uses the
statistics to pick up a candidate idle state and applies the utilization
heuristic to it and only then calls tick_nohz_get_sleep_length() to
obtain the sleep length value and refine the selection if necessary.
This change by itself does not cause tick_nohz_get_sleep_length() to
be called less often, but it prepares the code for subsequent changes
that will do so.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
Tested-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
|
|
Because the utilized field in struct teo_cpu is only used locally in
teo_select(), replace it with a local variable in that function.
No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-and-tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
|
|
When teo_select() is going to return early in some special cases, make
it avoid stopping the tick if the idle state to be returned is shallow.
In particular, never stop the tick if state 0 is to be returned.
Link: https://lore.kernel.org/linux-pm/CAJZ5v0jJxHj65r2HXBTd3wfbZtsg=_StzwO1kA5STDnaPe_dWA@mail.gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-and-tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
|
|
The TEO governor takes CPU utilization into account by refining idle state
selection when the utilization is above a certain threshold. This is done by
choosing an idle state shallower than the previously selected one.
However, when doing this, the idle duration estimate needs to be
adjusted so as to prevent the scheduler tick from being stopped when the
candidate idle state is shallow, which may lead to excessive energy
usage if the CPU is not woken up quickly enough going forward.
Moreover, if the scheduler tick has been stopped already and the new
idle duration estimate is too small, the replacement candidate state
cannot be used.
Modify the relevant code to take the above observations into account.
Fixes: 9ce0f7c4bc64 ("cpuidle: teo: Introduce util-awareness")
Link: https://lore.kernel.org/linux-pm/CAJZ5v0jJxHj65r2HXBTd3wfbZtsg=_StzwO1kA5STDnaPe_dWA@mail.gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-and-tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
|
|
Modern interactive systems, such as recent Android phones, tend to have
power efficient shallow idle states. Selecting deeper idle states on a
device while a latency-sensitive workload is running can adversely
impact performance due to increased latency. Additionally, if the CPU
wakes up from a deeper sleep before its target residency as is often the
case, it results in a waste of energy on top of that.
At the moment, none of the available idle governors take any scheduling
information into account. They also tend to overestimate the idle
duration quite often, which causes them to select excessively deep idle
states, thus leading to increased wakeup latency and lower performance
with no power saving. For 'menu' while web browsing on Android for
instance, those types of wakeups ('too deep') account for over 24% of
all wakeups.
At the same time, on some platforms idle state 0 can be power efficient
enough to warrant wanting to prefer it over idle state 1. This is
because the power usage of the two states can be so close that
sufficient amounts of too deep state 1 sleeps can completely offset the
state 1 power saving to the point where it would've been more power
efficient to just use state 0 instead. This is, of course, for systems
where state 0 is not a polling state, such as arm-based devices.
Sleeps that happened in state 0 while they could have used state 1 ('too
shallow') only save less power than they otherwise could have. Too deep
sleeps, on the other hand, harm performance and nullify the potential
power saving from using state 1 in the first place. While taking this
into account, it is clear that on balance it is preferable for an idle
governor to have more too shallow sleeps instead of more too deep sleeps
on those kinds of platforms.
This patch specifically tunes TEO to prefer shallower idle states in
order to reduce wakeup latency and achieve better performance.
To this end, before selecting the next idle state it uses the avg_util
signal of a CPU's runqueue in order to determine to what extent the CPU
is being utilized. This util value is then compared to a threshold
defined as a percentage of the CPU's capacity (capacity >> 6 ie. ~1.5%
in the current implementation). If the util is above the threshold, the
index of the idle state selected by TEO metrics will be reduced by 1,
thus selecting a shallower state. If the util is below the threshold,
the governor defaults to the TEO metrics mechanism to try to select the
deepest available idle state based on the closest timer event and its
own correctness.
The main goal of this is to reduce latency and increase performance for
some workloads. Under some workloads it will result in an increase in
power usage (Geekbench 5) while for other workloads it will also result
in a decrease in power usage compared to TEO (PCMark Web, Jankbench,
Speedometer).
It can provide drastically decreased latency and performance benefits in
certain types of workloads that are sensitive to latency.
Example test results:
1. GB5 (better score, latency & more power usage)
| metric | menu | teo | teo-util-aware |
| ------------------------------------- | -------------- | ----------------- | ----------------- |
| gmean score | 2826.5 (0.0%) | 2764.8 (-2.18%) | 2865 (1.36%) |
| gmean power usage [mW] | 2551.4 (0.0%) | 2606.8 (2.17%) | 2722.3 (6.7%) |
| gmean too deep % | 14.99% | 9.65% | 4.02% |
| gmean too shallow % | 2.5% | 5.96% | 14.59% |
| gmean task wakeup latency (asynctask) | 78.16μs (0.0%) | 61.60μs (-21.19%) | 54.45μs (-30.34%) |
2. Jankbench (better score, latency & less power usage)
| metric | menu | teo | teo-util-aware |
| ------------------------------------- | -------------- | ----------------- | ----------------- |
| gmean frame duration | 13.9 (0.0%) | 14.7 (6.0%) | 12.6 (-9.0%) |
| gmean jank percentage | 1.5 (0.0%) | 2.1 (36.99%) | 1.3 (-17.37%) |
| gmean power usage [mW] | 144.6 (0.0%) | 136.9 (-5.27%) | 121.3 (-16.08%) |
| gmean too deep % | 26.00% | 11.00% | 2.54% |
| gmean too shallow % | 4.74% | 11.89% | 21.93% |
| gmean wakeup latency (RenderThread) | 139.5μs (0.0%) | 116.5μs (-16.49%) | 91.11μs (-34.7%) |
| gmean wakeup latency (surfaceflinger) | 124.0μs (0.0%) | 151.9μs (22.47%) | 87.65μs (-29.33%) |
Signed-off-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
[ rjw: Comment edits and white space adjustments ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Add a no_poll flag to teo_find_shallower_state() that will let the
function optionally not consider polling states.
This allows the caller to guard against the function inadvertently
resulting in TEO putting the CPU in a polling state when that
behaviour is undesirable.
Signed-off-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Rename two local variables in teo_select() so that their names better
reflect their purpose.
No functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
There are three mistakes in the loop in teo_select() that is looking
for an alternative candidate idle state. First, it should walk all
of the idle states shallower than the current candidate one,
including all of the disabled ones, but it terminates after the first
enabled idle state. Second, it should not terminate its last step
if idle state 0 is disabled (which is related to the first issue).
Finally, it may return the current alternative candidate idle state
prematurely if the time span criterion is not met by the idle state
under consideration at the moment.
To address the issues mentioned above, make the loop in question walk
all of the idle states shallower than the current candidate idle state
all the way down to idle state 0 and rearrange the checks in it.
Fixes: 77577558f25d ("cpuidle: teo: Rework most recent idle duration values treatment")
Reported-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Fix following coccicheck warning:
drivers/cpuidle/governors/teo.c:315:10-11: Unneeded semicolon
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
There are two descriptions of the TEO (Timer Events Oriented) cpuidle
governor in the kernel source tree, one in the C file containing its
code and one in cpuidle.rst which is part of admin-guide.
Instead of trying to keep them both in sync and in order to reduce
text duplication, include the governor description from the C file
directly into cpuidle.rst.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
The TEO (Timer Events Oriented) cpuidle governor uses several most
recent idle duration values for a given CPU to refine the idle state
selection in case the previous long-term trends have not been
followed recently and a new trend appears to be forming. That is
done by computing the average of the most recent idle duration
values falling below the time till the next timer event ("sleep
length"), provided that they are the majority of the most recent
idle duration values taken into account, and using it as the new
expected idle duration value.
However, idle state selection based on that value may not be optimal,
because the average does not really indicate which of the idle states
with target residencies less than or equal to it is likely to be the
best fit.
Thus, instead of computing the average, make the governor carry out
computations based on the distribution of the most recent idle
duration values among the bins corresponding to different idle
states. Namely, if the majority of the most recent idle duration
values taken into consideration are less than the current sleep
length (which means that the CPU is likely to wake up early), find
the idle state closest to the "candidate" one "matching" the sleep
length whose target residency is less than or equal to the majority
of the most recent idle duration values that have fallen below the
current sleep length (which means that it is likely to be "shallow
enough" this time).
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Two aspects of the current main idle state selection logic in the
TEO (Timer Events Oriented) cpuidle governor are quite questionable.
First of all, the "hits" and "misses" metrics used by it are only
updated for a given idle state if the time till the next timer event
("sleep length") is between the target residency of that state and
the target residency of the next one. Consequently, they are likely
to become stale if the sleep length tends to fall outside that
interval which increases the likelihood of subomtimal idle state
selection.
Second, the decision on whether or not to select the idle state
"matching" the sleep length is based on the metrics collected for
that state alone, whereas in principle the metrics collected for
the other idle states should be taken into consideration when that
decision is made. For example, if the measured idle duration is less
than the target residency of the idle state "matching" the sleep
length, then it is also less than the target residency of any deeper
idle state and that should be taken into account when considering
whether or not to select any of those states, but currently it is
not.
In order to address the above shortcomings, modify the main idle
state selection logic in the TEO governor to take the metrics
collected for all of the idle states into account when deciding
whether or not to select the one "matching" the sleep length.
Moreover, drop the "misses" metric that becomes redundant after the
above change and rename the "early_hits" metric to "intercepts" so
that its role is better reflected by its name (the idea being that
if a CPU wakes up earlier than indicated by the sleep length, then
it must be a result of a non-timer interrupt that "intercepts" the
CPU).
Also rename the states[] array in struct struct teo_cpu to
state_bins[] to avoid confusing it with the states[] array in
struct cpuidle_driver and update the documentation to match the
new code (and make it more comprehensive while at it).
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Initialize local variables in teo_select() where they are declared.
No functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Rename a local variable in teo_update() so that its purpose is better
reflected by its name and use one more local variable in the loop
over the CPU idle states in that function to make the code somewhat
easier to read.
No functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Modify the TEO governor to take possible negative return values of
tick_nohz_get_next_hrtimer() into account by changing the data type
of some variables used by it to s64 which allows it to carry out
computations without potentially problematic data type conversions
into u64.
Also change the computations in teo_select() so that the negative
values themselves are handled in a natural way to avoid adding extra
negative value checks to that function.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
If the time till the next timer event is shorter than the target
residency of the first idle state (state 0), the TEO governor does
not update its metrics for any idle states, but arguably it should
record a "hit" for idle state 0 in that case, so modify it to do
that.
Accordingly, also make it record an "early hit" for idle state 0 if
the measured idle duration is less than its target residency, which
allows one branch more to be dropped from teo_update().
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Fix a simple bug in rotating array index.
Fixes: b26bf6ab716f ("cpuidle: New timer events oriented governor for tickless systems")
Signed-off-by: Ikjoon Jang <ikjn@chromium.org>
Cc: 5.1+ <stable@vger.kernel.org> # 5.1+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
There are three places in teo_select() where a given amount of time
is compared with TICK_NSEC if tick_nohz_tick_stopped() returns true,
which is a bit of duplicated code.
Avoid that code duplication by defining a helper function to do the
check and using it in all of the places in question.
No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
If the current state with the maximum "early hits" metric in
teo_select() is also the one "matching" the expected idle duration,
it will be used as the candidate one for selection even if its
"misses" metric is greater than its "hits" metric, which is not
correct.
In that case, the candidate state should be shallower than the
current one and its "early hits" metric should be the maximum
among the idle states shallower than the current one.
To make that happen, modify teo_select() to save the index of
the state whose "early hits" metric is the maximum for the
range of states below the current one and go back to that state
if it turns out that the current one should be rejected.
Fixes: 159e48560f51 ("cpuidle: teo: Fix "early hits" handling for disabled idle states")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
One purpose of the computations in teo_update() is to determine
whether or not the (saved) time till the next timer event and the
measured idle duration fall into the same "bin", so avoid using
values that include the cpuidle overhead to obtain the latter.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Currently, the cpuidle subsystem uses microseconds as the unit of
time which (among other things) causes the idle loop to incur some
integer division overhead for no clear benefit.
In order to allow cpuidle to measure time in nanoseconds, add two
new fields, exit_latency_ns and target_residency_ns, to represent the
exit latency and target residency of an idle state in nanoseconds,
respectively, to struct cpuidle_state and initialize them with the
help of the corresponding values in microseconds provided by drivers.
Additionally, change cpuidle_governor_latency_req() to return the
idle state exit latency constraint in nanoseconds.
Also meeasure idle state residency (last_residency_ns in struct
cpuidle_device and time_ns in struct cpuidle_driver) in nanoseconds
and update the cpuidle core and governors accordingly.
However, the menu governor still computes typical intervals in
microseconds to avoid integer overflows.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
|
|
There are two reasons why CPU idle states may be disabled: either
because the driver has disabled them or because they have been
disabled by user space via sysfs.
In the former case, the state's "disabled" flag is set once during
the initialization of the driver and it is never cleared later (it
is read-only effectively). In the latter case, the "disable" field
of the given state's cpuidle_state_usage struct is set and it may be
changed via sysfs. Thus checking whether or not an idle state has
been disabled involves reading these two flags every time.
In order to avoid the additional check of the state's "disabled" flag
(which is effectively read-only anyway), use the value of it at the
init time to set a (new) flag in the "disable" field of that state's
cpuidle_state_usage structure and use the sysfs interface to
manipulate another (new) flag in it. This way the state is disabled
whenever the "disable" field of its cpuidle_state_usage structure is
nonzero, whatever the reason, and it is the only place to look into
to check whether or not the state has been disabled.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
|
|
The TEO governor uses idle duration "bins" defined in accordance with
the CPU idle states table provided by the driver, so that each "bin"
covers the idle duration range between the target residency of the
idle state corresponding to it and the target residency of the closest
deeper idle state. The governor collects statistics for each bin
regardless of whether or not the idle state corresponding to it is
currently enabled.
In particular, the "early hits" metric measures the likelihood of a
situation in which the idle duration measured after wakeup falls into
to given bin, but the time till the next timer (sleep length) falls
into a bin corresponding to one of the deeper idle states. It is
used when the "hits" and "misses" metrics indicate that the state
"matching" the sleep length should not be selected, so that the state
with the maximum "early hits" value is selected instead of it.
If the idle state corresponding to the given bin is disabled, it
cannot be selected and if it turns out to be the one that should be
selected, a shallower idle state needs to be used instead of it.
Nevertheless, the metrics collected for the bin corresponding to it
are still valid and need to be taken into account as though that
state had not been disabled.
As far as the "early hits" metric is concerned, teo_select() tries to
take disabled states into account, but the state index corresponding
to the maximum "early hits" value computed by it may be incorrect.
Namely, it always uses the index of the previous maximum "early hits"
state then, but there may be enabled idle states closer to the
disabled one in question. In particular, if the current candidate
state (whose index is the idx value) is closer to the disabled one
and the "early hits" value of the disabled state is greater than the
current maximum, the index of the current candidate state (idx)
should replace the "maximum early hits state" index.
Modify the code to handle that case correctly.
Fixes: b26bf6ab716f ("cpuidle: New timer events oriented governor for tickless systems")
Reported-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 5.1+ <stable@vger.kernel.org> # 5.1+
|
|
The TEO governor uses idle duration "bins" defined in accordance with
the CPU idle states table provided by the driver, so that each "bin"
covers the idle duration range between the target residency of the
idle state corresponding to it and the target residency of the closest
deeper idle state. The governor collects statistics for each bin
regardless of whether or not the idle state corresponding to it is
currently enabled.
In particular, the "hits" and "misses" metrics measure the likelihood
of a situation in which both the time till the next timer (sleep
length) and the idle duration measured after wakeup fall into the
given bin. Namely, if the "hits" value is greater than the "misses"
one, that situation is more likely than the one in which the sleep
length falls into the given bin, but the idle duration measured after
wakeup falls into a bin corresponding to one of the shallower idle
states.
If the idle state corresponding to the given bin is disabled, it
cannot be selected and if it turns out to be the one that should be
selected, a shallower idle state needs to be used instead of it.
Nevertheless, the metrics collected for the bin corresponding to it
are still valid and need to be taken into account as though that
state had not been disabled.
For this reason, make teo_select() always use the "hits" and "misses"
values of the idle duration range that the sleep length falls into
even if the specific idle state corresponding to it is disabled and
if the "hits" values is greater than the "misses" one, select the
closest enabled shallower idle state in that case.
Fixes: b26bf6ab716f ("cpuidle: New timer events oriented governor for tickless systems")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 5.1+ <stable@vger.kernel.org> # 5.1+
|
|
Rename a local variable in teo_select() in preparation for subsequent
code modifications, no intentional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 5.1+ <stable@vger.kernel.org> # 5.1+
|
|
Prevent disabled CPU idle state with target residencies beyond the
anticipated idle duration from being taken into account by the TEO
governor.
Fixes: b26bf6ab716f ("cpuidle: New timer events oriented governor for tickless systems")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 5.1+ <stable@vger.kernel.org> # 5.1+
|
|
Notice that setting measured_us to UINT_MAX in teo_update() earlier
doesn't change the behavior of the following code, so do that and
eliminate a redundant check used for setting measured_us to UINT_MAX.
This change is not expected to alter functionality.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
The TEO goveror prevents the scheduler tick from being stopped (unless
stopped already) if there is a PM QoS latency constraint for the given
CPU and the target residency of the deepest idle state matching that
constraint is below the tick boundary.
However, that is problematic if CPUs with PM QoS latency constraints
are idle for long times, because it effectively causes the tick to
run on them all the time which is wasteful. [It is also confusing
and questionable if they are full dynticks CPUs.]
To address that issue, modify the TEO governor to carry out the
entire search for the most suitable idle state (from the target
residency perspective) even if a latency constraint is present,
to allow it to determine the expected idle duration in all cases.
Also, when using the last several measured idle duration values
to refine the idle state selection, make it compare those values
with the current expected idle duration value (instead of
comparing them with the target residency of the idle state
selected so far) which should prevent the tick from being
retained when it makes sense to stop it sometimes (especially
in the presence of PM QoS latency constraints).
Fixes: b26bf6ab716f ("cpuidle: New timer events oriented governor for tickless systems")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Since this field is shared by all governors, move it to
cpuidle device structure.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
The venerable menu governor does some things that are quite
questionable in my view.
First, it includes timer wakeups in the pattern detection data and
mixes them up with wakeups from other sources which in some cases
causes it to expect what essentially would be a timer wakeup in a
time frame in which no timer wakeups are possible (because it knows
the time until the next timer event and that is later than the
expected wakeup time).
Second, it uses the extra exit latency limit based on the predicted
idle duration and depending on the number of tasks waiting on I/O,
even though those tasks may run on a different CPU when they are
woken up. Moreover, the time ranges used by it for the sleep length
correction factors depend on whether or not there are tasks waiting
on I/O, which again doesn't imply anything in particular, and they
are not correlated to the list of available idle states in any way
whatever.
Also, the pattern detection code in menu may end up considering
values that are too large to matter at all, in which cases running
it is a waste of time.
A major rework of the menu governor would be required to address
these issues and the performance of at least some workloads (tuned
specifically to the current behavior of the menu governor) is likely
to suffer from that. It is thus better to introduce an entirely new
governor without them and let everybody use the governor that works
better with their actual workloads.
The new governor introduced here, the timer events oriented (TEO)
governor, uses the same basic strategy as menu: it always tries to
find the deepest idle state that can be used in the given conditions.
However, it applies a different approach to that problem.
First, it doesn't use "correction factors" for the time till the
closest timer, but instead it tries to correlate the measured idle
duration values with the available idle states and use that
information to pick up the idle state that is most likely to "match"
the upcoming CPU idle interval.
Second, it doesn't take the number of "I/O waiters" into account at
all and the pattern detection code in it avoids taking timer wakeups
into account. It also only uses idle duration values less than the
current time till the closest timer (with the tick excluded) for that
purpose.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
|
