This change is based on the observation that it is not in fact necessary
to select a deep idle state every time the scheduler tick has been
stopped before the idle state selection takes place. Namely, if the
time till the closest timer (that is not the tick) is short enough,
a shallow idle state can be selected because the timer will kick the
CPU out of that state, so the damage from a possible overly optimistic
selection will be limited.
Update the menu governor in accordance with the above and use twice
the tick period length as the "safe timer range" for allowing the
original predicted_ns value to be used even if the tick has been
stopped.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/3341782.5fSG56mABF@rafael.j.wysocki
cpuidle systems where the governor has no choice because there's only
a single idle state are now handled by cpuidle core and bypass the
governor, so remove the related handling.
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
[ rjw: Rebase on top of the cpuidle changes merged recently ]
Link: https://patch.msgid.link/20260216185005.1131593-5-aboorvad@linux.ibm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
After commit 5484e31bbb ("cpuidle: menu: Skip tick_nohz_get_sleep_length()
call in some cases"), if the return value of get_typical_interval()
multiplied by NSEC_PER_USEC is not greater than RESIDENCY_THRESHOLD_NS,
the menu governor will skip computing the time till the closest timer.
If that happens when the tick has been stopped already, the selected
idle state may be too deep due to the subsequent check comparing
predicted_ns with TICK_NSEC and causing its value to be replaced with
the expected time till the closest timer, which is KTIME_MAX in that
case. That will cause the deepest enabled idle state to be selected,
but the time till the closest timer very well may be shorter than the
target residency of that state, in which case a shallower state should
be used.
Address this by making menu_select() always compute the time till the
closest timer when the tick has been stopped.
Also move the predicted_ns check mentioned above into the branch in
which the time till the closest timer is determined because it only
needs to be done in that case.
Fixes: 5484e31bbb ("cpuidle: menu: Skip tick_nohz_get_sleep_length() call in some cases")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/5959091.DvuYhMxLoT@rafael.j.wysocki
The unlikely() annotation on the early-return condition in menu_select()
is incorrect on systems with only one idle state (e.g., ARM64 servers
with a single ACPI LPI state). Branch profiling shows 100% misprediction
on such systems since drv->state_count <= 1 is always true.
On platforms where only state0 is available, this path is the common
case, not an unlikely edge case. Remove the misleading annotation to
let the branch predictor learn the actual behavior.
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260105-annotated_idle-v1-1-10ddf0771b58@debian.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
On virtualized PowerPC (pseries) systems, where only one polling state
(Snooze) and one deep state (CEDE) are available, selecting CEDE when
the predicted idle duration is less than the target residency of CEDE
state can hurt performance. In such cases, the entry/exit overhead of
CEDE outweighs the power savings, leading to unnecessary state
transitions and higher latency.
Menu governor currently contains a special-case rule that prioritizes
the first non-polling state over polling, even when its target residency
is much longer than the predicted idle duration. On PowerPC/pseries,
where the gap between the polling state (Snooze) and the first non-polling
state (CEDE) is large, this behavior causes performance regressions.
Refine that special case by adding an extra requirement: the first
non-polling state can only be chosen if its target residency is below
the defined RESIDENCY_THRESHOLD_NS. If this condition is not satisfied,
polling is allowed instead, avoiding suboptimal non-polling state
entries.
This change is limited to the single special-case rule for the first
non-polling state. The general non-polling state selection logic in the
menu governor remains unchanged.
Performance improvement observed with pgbench on PowerPC (pseries)
system:
+---------------------------+------------+------------+------------+
| Metric | Baseline | Patched | Change (%) |
+---------------------------+------------+------------+------------+
| Transactions/sec (TPS) | 495,210 | 536,982 | +8.45% |
| Avg latency (ms) | 0.163 | 0.150 | -7.98% |
+---------------------------+------------+------------+------------+
CPUIdle state usage:
+--------------+--------------+-------------+
| Metric | Baseline | Patched |
+--------------+--------------+-------------+
| Total usage | 12,735,820 | 13,918,442 |
| Above usage | 11,401,520 | 1,598,210 |
| Below usage | 20,145 | 702,395 |
+--------------+--------------+-------------+
Above/Total and Below/Total usage percentages:
+------------------------+-----------+---------+
| Metric | Baseline | Patched |
+------------------------+-----------+---------+
| Above % (Above/Total) | 89.56% | 11.49% |
| Below % (Below/Total) | 0.16% | 5.05% |
| Total cpuidle miss (%) | 89.72% | 16.54% |
+------------------------+-----------+---------+
The results indicate that restricting CEDE selection to cases where
its residency matches the predicted idle time reduces mispredictions,
lowers unnecessary state transitions, and improves overall throughput.
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
[ rjw: Changelog edits, rebase ]
Link: https://patch.msgid.link/20251006013954.17972-1-aboorvad@linux.ibm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
A throughput regression of 11% introduced by commit 779b1a1cb1 ("cpuidle:
governors: menu: Avoid selecting states with too much latency") has been
reported and it is related to the case when the menu governor checks if
selecting a proper idle state instead of a polling one makes sense.
In particular, it is questionable to do so if the exit latency of the
idle state in question exceeds the predicted idle duration, so add a
check for that, which is sufficient to make the reported regression go
away, and update the related code comment accordingly.
Fixes: 779b1a1cb1 ("cpuidle: governors: menu: Avoid selecting states with too much latency")
Closes: https://lore.kernel.org/linux-pm/004501dc43c9$ec8aa930$c59ffb90$@telus.net/
Reported-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/12786727.O9o76ZdvQC@rafael.j.wysocki
It is reported that commit 85975daeaa ("cpuidle: menu: Avoid discarding
useful information") led to a performance regression on Intel Jasper Lake
systems because it reduced the time spent by CPUs in idle state C7 which
is correlated to the maximum frequency the CPUs can get to because of an
average running power limit [1].
Before that commit, get_typical_interval() would have returned UINT_MAX
whenever it had been unable to make a high-confidence prediction which
had led to selecting the deepest available idle state too often and
both power and performance had been inadequate as a result of that on
some systems. However, this had not been a problem on systems with
relatively aggressive average running power limits, like the Jasper Lake
systems in question, because on those systems it was compensated by the
ability to run CPUs faster.
It was addressed by causing get_typical_interval() to return a number
based on the recent idle duration information available to it even if it
could not make a high-confidence prediction, but that clearly did not
take the possible correlation between idle power and available CPU
capacity into account.
For this reason, revert most of the changes made by commit 85975daeaa,
except for one cosmetic cleanup, and add a comment explaining the
rationale for returning UINT_MAX from get_typical_interval() when it
is unable to make a high-confidence prediction.
Fixes: 85975daeaa ("cpuidle: menu: Avoid discarding useful information")
Closes: https://lore.kernel.org/linux-pm/36iykr223vmcfsoysexug6s274nq2oimcu55ybn6ww4il3g3cv@cohflgdbpnq7/ [1]
Reported-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/3663603.iIbC2pHGDl@rafael.j.wysocki
Reduce the indentation level in the main loop of menu_select() by
rearranging some checks and assignments in it.
No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/2389215.ElGaqSPkdT@rafael.j.wysocki
Occasionally, the exit latency of the idle state selected by the menu
governor may exceed the PM QoS CPU wakeup latency limit. Namely, if the
scheduler tick has been stopped already and predicted_ns is greater than
the tick period length, the governor may return an idle state whose exit
latency exceeds latency_req because that decision is made before
checking the current idle state's exit latency.
For instance, say that there are 3 idle states, 0, 1, and 2. For idle
states 0 and 1, the exit latency is equal to the target residency and
the values are 0 and 5 us, respectively. State 2 is deeper and has the
exit latency and target residency of 200 us and 2 ms (which is greater
than the tick period length), respectively.
Say that predicted_ns is equal to TICK_NSEC and the PM QoS latency
limit is 20 us. After the first two iterations of the main loop in
menu_select(), idx becomes 1 and in the third iteration of it the target
residency of the current state (state 2) is greater than predicted_ns.
State 2 is not a polling one and predicted_ns is not less than TICK_NSEC,
so the check on whether or not the tick has been stopped is done. Say
that the tick has been stopped already and there are no imminent timers
(that is, delta_tick is greater than the target residency of state 2).
In that case, idx becomes 2 and it is returned immediately, but the exit
latency of state 2 exceeds the latency limit.
Address this issue by modifying the code to compare the exit latency of
the current idle state (idle state i) with the latency limit before
comparing its target residency with predicted_ns, which allows one
more exit_latency_ns check that becomes redundant to be dropped.
However, after the above change, latency_req cannot take the predicted_ns
value any more, which takes place after commit 38f83090f5 ("cpuidle:
menu: Remove iowait influence"), because it may cause a polling state
to be returned prematurely.
In the context of the previous example say that predicted_ns is 3000 and
the PM QoS latency limit is still 20 us. Additionally, say that idle
state 0 is a polling one. Moving the exit_latency_ns check before the
target_residency_ns one causes the loop to terminate in the second
iteration, before the target_residency_ns check, so idle state 0 will be
returned even though previously state 1 would be returned if there were
no imminent timers.
For this reason, remove the assignment of the predicted_ns value to
latency_req from the code.
Fixes: 5ef499cd57 ("cpuidle: menu: Handle stopped tick more aggressively")
Cc: 4.17+ <stable@vger.kernel.org> # 4.17+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/5043159.31r3eYUQgx@rafael.j.wysocki
Marc has reported that commit 85975daeaa ("cpuidle: menu: Avoid
discarding useful information") caused the number of wakeup interrupts
to increase on an idle system [1], which was not expected to happen
after merely allowing shallower idle states to be selected by the
governor in some cases.
However, on the system in question, all of the idle states deeper than
WFI are rejected by the driver due to a firmware issue [2]. This causes
the governor to only consider the recent interval duriation data
corresponding to attempts to enter WFI that are successful and the
recent invervals table is filled with values lower than the scheduler
tick period. Consequently, the governor predicts an idle duration
below the scheduler tick period length and avoids stopping the tick
more often which leads to the observed symptom.
Address it by modifying the governor to update the recent intervals
table also when entering the previously selected idle state fails, so
it knows that the short idle intervals might have been the minority
had the selected idle states been actually entered every time.
Fixes: 85975daeaa ("cpuidle: menu: Avoid discarding useful information")
Link: https://lore.kernel.org/linux-pm/86o6sv6n94.wl-maz@kernel.org/ [1]
Link: https://lore.kernel.org/linux-pm/7ffcb716-9a1b-48c2-aaa4-469d0df7c792@arm.com/ [2]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/2793874.mvXUDI8C0e@rafael.j.wysocki
Directly assign the last bucket value instead of calling which_bucket()
when next_timer_ns equals KTIME_MAX, the largest possible value that
always falls into the last bucket.
This avoids unnecessary calculations and enhances performance.
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Zhongqiu Han <quic_zhonhan@quicinc.com>
Link: https://patch.msgid.link/20250405135308.1854342-1-quic_zhonhan@quicinc.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
The documentation of the menu cpuidle governor needs to be updated
to match the code behavior after some changes made recently.
No functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/4998484.31r3eYUQgx@rjwysocki.net
[ rjw: More specific subject, two typos fixed in the changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
When giving up on making a high-confidence prediction,
get_typical_interval() always returns UINT_MAX which means that the
next idle interval prediction will be based entirely on the time till
the next timer. However, the information represented by the most
recent intervals may not be completely useless in those cases.
Namely, the largest recent idle interval is an upper bound on the
recently observed idle duration, so it is reasonable to assume that
the next idle duration is unlikely to exceed it. Moreover, this is
still true after eliminating the suspected outliers if the sample
set still under consideration is at least as large as 50% of the
maximum sample set size.
Accordingly, make get_typical_interval() return the current maximum
recent interval value in that case instead of UINT_MAX.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reported-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Link: https://patch.msgid.link/7770672.EvYhyI6sBW@rjwysocki.net
Currently, get_typical_interval() attempts to eliminate outliers at the
high end of the sample set only (probably in order to bias the prediction
toward lower values), but this it problematic because if the outliers are
present at the low end of the sample set, discarding the highest values
will not help to reduce the variance.
Since the presence of outliers at the low end of the sample set is
generally as likely as their presence at the high end of the sample
set, modify get_typical_interval() to treat samples at the largest
distances from the average (on both ends of the sample set) as outliers.
This should increase the likelihood of making a meaningful prediction
in some cases.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reported-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Link: https://patch.msgid.link/2301940.iZASKD2KPV@rjwysocki.net
To prepare get_typical_interval() for subsequent changes, rearrange
the use of the data point threshold in it a bit and initialize that
threshold to UINT_MAX which is more consistent with its data type.
No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Link: https://patch.msgid.link/8490144.T7Z3S40VBb@rjwysocki.net
Use the observation that one loop is sufficient to compute the average
of an array of values and their variance to eliminate one of the loops
from get_typical_interval().
While at it, make get_typical_interval() consistently use u64 as the
64-bit unsigned integer data type and rearrange some white space and the
declarations of local variables in it (to make them follow the reverse
X-mas tree pattern).
No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Link: https://patch.msgid.link/3339073.aeNJFYEL58@rjwysocki.net
Local variable min in get_typical_interval() is updated, but never
accessed later, so drop it.
No functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Link: https://patch.msgid.link/13699686.uLZWGnKmhe@rjwysocki.net
Remove CPU iowaiters influence on idle state selection.
Remove the menu notion of performance multiplier which increased with
the number of tasks that went to iowait sleep on this CPU and haven't
woken up yet.
Relying on iowait for cpuidle is problematic for a few reasons:
1. There is no guarantee that an iowaiting task will wake up on the
same CPU.
2. The task being in iowait says nothing about the idle duration, we
could be selecting shallower states for a long time.
3. The task being in iowait doesn't always imply a performance hit
with increased latency.
4. If there is such a performance hit, the number of iowaiting tasks
doesn't directly correlate.
5. The definition of iowait altogether is vague at best, it is
sprinkled across kernel code.
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20240905092645.2885200-2-christian.loehle@arm.com
[ rjw: Minor edits in the changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
The performance impact of loadavg was removed with commit a7fe5190c0
("cpuidle: menu: Remove get_loadavg() from the performance multiplier")
With only iowait remaining the description can be simplified, remove
also the no longer needed includes.
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
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>
The word `these' in a comment is repeated, so drop one.
Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Make the menu governor check the tick_nohz_get_next_hrtimer()
return value so as to avoid dealing with negative "sleep length"
values and make it use that value directly when the tick is stopped.
While at it, rename local variable delta_next in menu_select() to
delta_tick which better reflects its purpose.
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>
After commit 554c8aa8ec ("sched: idle: Select idle state before
stopping the tick") the menu governor 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, make the menu governor allow the tick to be
stopped only if the idle duration predicted by it is beyond the tick
boundary, except when the shallowest idle state is selected upfront
and it is not a "polling" one.
Fixes: 554c8aa8ec ("sched: idle: Select idle state before stopping the tick")
Link: https://lore.kernel.org/lkml/79b247b3-e056-610e-9a07-e685dfdaa6c9@gmail.com/
Reported-by: Thomas Lindroth <thomas.lindroth@gmail.com>
Tested-by: Thomas Lindroth <thomas.lindroth@gmail.com>
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>
Based on 1 normalized pattern(s):
this code is licenced under the gpl version 2 as described in the
copying file that acompanies the linux kernel
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 1 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190528171439.466585205@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The variance computation in get_typical_interval() may overflow if
the square of the value of diff exceeds the maximum for the int64_t
data type value which basically is the case when it is of the order
of UINT_MAX.
However, data points so far in the future don't matter for idle
state selection anyway, so change the initial threshold value in
get_typical_interval() to INT_MAX which will cause more "outlying"
data points to be discarded without affecting the selection result.
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
- Fix build regression in the intel_pstate driver that doesn't
build without CONFIG_ACPI after recent changes (Dominik Brodowski).
- One of the heuristics in the menu cpuidle governor is based on a
function returning 0 most of the time, so drop it and clean up
the scheduler code related to it (Daniel Lezcano).
- Prevent the arm_big_little cpufreq driver from being used on ARM64
which is not suitable for it and drop the arm_big_little_dt driver
that is not used any more (Sudeep Holla).
- Prevent the hung task watchdog from triggering during resume from
system-wide sleep states by disabling it before freezing tasks and
enabling it again after they have been thawed (Vitaly Kuznetsov).
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Merge tag 'pm-4.20-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
Pull more power management updates from Rafael Wysocki:
"These remove a questionable heuristic from the menu cpuidle governor,
fix a recent build regression in the intel_pstate driver, clean up ARM
big-Little support in cpufreq and fix up hung task watchdog's
interaction with system-wide power management transitions.
Specifics:
- Fix build regression in the intel_pstate driver that doesn't build
without CONFIG_ACPI after recent changes (Dominik Brodowski).
- One of the heuristics in the menu cpuidle governor is based on a
function returning 0 most of the time, so drop it and clean up the
scheduler code related to it (Daniel Lezcano).
- Prevent the arm_big_little cpufreq driver from being used on ARM64
which is not suitable for it and drop the arm_big_little_dt driver
that is not used any more (Sudeep Holla).
- Prevent the hung task watchdog from triggering during resume from
system-wide sleep states by disabling it before freezing tasks and
enabling it again after they have been thawed (Vitaly Kuznetsov)"
* tag 'pm-4.20-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
kernel: hung_task.c: disable on suspend
cpufreq: remove unused arm_big_little_dt driver
cpufreq: drop ARM_BIG_LITTLE_CPUFREQ support for ARM64
cpufreq: intel_pstate: Fix compilation for !CONFIG_ACPI
cpuidle: menu: Remove get_loadavg() from the performance multiplier
sched: Factor out nr_iowait and nr_iowait_cpu
There are several definitions of those functions/macros in places that
mess with fixed-point load averages. Provide an official version.
[akpm@linux-foundation.org: fix missed conversion in block/blk-iolatency.c]
Link: http://lkml.kernel.org/r/20180828172258.3185-5-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Suren Baghdasaryan <surenb@google.com>
Tested-by: Daniel Drake <drake@endlessm.com>
Cc: Christopher Lameter <cl@linux.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <jweiner@fb.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Enderborg <peter.enderborg@sony.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vinayak Menon <vinmenon@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The function get_loadavg() returns almost always zero. To be more
precise, statistically speaking for a total of 1023379 times passing
in the function, the load is equal to zero 1020728 times, greater than
100, 610 times, the remaining is between 0 and 5.
In 2011, the get_loadavg() was removed from the Android tree because
of the above [1]. At this time, the load was:
unsigned long this_cpu_load(void)
{
struct rq *this = this_rq();
return this->cpu_load[0];
}
In 2014, the code was changed by commit 372ba8cb46 (cpuidle: menu: Lookup CPU
runqueues less) and the load is:
void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
{
struct rq *rq = this_rq();
*nr_waiters = atomic_read(&rq->nr_iowait);
*load = rq->load.weight;
}
with the same result.
Both measurements show using the load in this code path does no matter
anymore. Removing it.
[1] 4dedd9f124
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
If the minimum interval taken into account in the average computation
loop in get_typical_interval() is less than the expected idle
duration determined so far, the resultant average cannot be greater
than that value as well and the entire return result of the function
is going to be discarded anyway going forward.
In that case, it is a waste of time to carry out the remaining
computations in get_typical_interval(), so avoid that by returning
early if the minimum interval is not below the expected idle duration.
No intentional changes of behavior.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Since the correction factor cannot be greater than RESOLUTION * DECAY,
the result of the predicted_us computation in menu_select() cannot be
greater than data->next_timer_us, so it is not necessary to compare
the "typical interval" value coming from get_typical_interval() with
data->next_timer_us separately.
It is sufficient to copmare predicted_us with the return value of
get_typical_interval() directly, so do that and drop the now
redundant expected_interval variable.
No intentional changes of behavior.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
After some recent menu governor changes, the promotion of the
"polling" state to a physical one is mostly controlled by the
latency limit (resulting from the "interactivity" factor) and
not by the time to the closest timer event, so it should be
sufficient to check the exit latency of that state for this
purpose (of course, its target residency still needs to be
within the next timer event range for energy-efficiency).
Also, the physical state the "polling" one is promoted to need not
be the next one in principle (in case the next state is disabled,
for example).
For these reasons, simplify the checks made to decide whether or
not to promote the "polling" state to a physical one and update
the target idle duration when it is promoted in case the residency
of the new state turns out to be above the tick boundary (in which
case there is no reason to stop the tick).
Tested-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
It is better to always update data->bucket before returning from
menu_select() to avoid updating the correction factor for a stale
bucket, so combine the latency_req == 0 special check with the more
general check below.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
If the next timer event (not including the tick) is closer than the
target residency of the second state or the PM QoS latency constraint
is below its exit latency, state[0] will be used regardless of any
other factors, so skip the computations in menu_select() then and
return 0 straight away from it.
Still, do that after the bucket has been determined to avoid
updating the correction factor for a stale bucket.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
It is not necessary to update data->last_state_idx in menu_select()
as it only is used in menu_update() which only runs when
data->needs_update is set and that is set only when updating
data->last_state_idx in menu_reflect().
Accordingly, drop the update of data->last_state_idx from
menu_select() and get rid of the (now redundant) "out" label
from it.
No intentional behavior changes.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Rearrange the code in menu_select() so that the loop over idle states
always starts from 0 and get rid of the first_idx variable.
While at it, add two empty lines to separate conditional statements
from one another.
No intentional behavior changes.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Since menu_select() can only set first_idx to 1 if the exit latency
of the second state is not greater than the latency limit, it should
first determine that limit. Thus first_idx should be computed after
the "interactivity" factor has been taken into account.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewedy-by: Daniel Lezcano <daniel.lezcano@linaro.org>
If the CPU exits the "polling" state due to the time limit in the
loop in poll_idle(), this is not a real wakeup and it just means
that the "polling" state selection was not adequate. The governor
mispredicted short idle duration, but had a more suitable state been
selected, the CPU might have spent more time in it. In fact, there
is no reason to expect that there would have been a wakeup event
earlier than the next timer in that case.
Handling such cases as regular wakeups in menu_update() may cause the
menu governor to make suboptimal decisions going forward, but ignoring
them altogether would not be correct either, because every time
menu_select() is invoked, it makes a separate new attempt to predict
the idle duration taking distinct time to the closest timer event as
input and the outcomes of all those attempts should be recorded.
For this reason, make menu_update() always assume that if the
"polling" state was exited due to the time limit, the next proper
wakeup event for the CPU would be the next timer event (not
including the tick).
Fixes: a37b969a61 "cpuidle: poll_state: Add time limit to poll_idle()"
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
The predicted_us field in struct menu_device is only accessed in
menu_select(), so replace it with a local variable in that function.
With that, stop using expected_interval instead of predicted_us to
store the new predicted idle duration value if it is set to the
selected state's target residency which is quite confusing.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
cpuidle_get_last_residency() is just a wrapper for retrieving
the last_residency member of struct cpuidle_device. It's also
weirdly the only wrapper function for accessing cpuidle_* struct
member (by my best guess is it could be a leftover from v2.x).
Anyhow, since the only two users (the ladder and menu governors)
can access dev->last_residency directly, and it's more intuitive to
do it that way, let's just get rid of the wrapper.
This patch tidies up CPU idle code a bit without functional changes.
Signed-off-by: Fieah Lim <kw@fieahl.im>
[ rjw: Changelog cleanup ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
The case addressed by commit 5ef499cd57 (cpuidle: menu: Handle
stopped tick more aggressively) in the stopped tick case is present
when the tick has not been stopped yet too. Namely, if only two CPU
idle states, shallow state A with target residency significantly
below the tick boundary and deep state B with target residency
significantly above it, are available and the predicted idle
duration is above the tick boundary, but below the target residency
of state B, state A will be selected and the CPU may spend indefinite
amount of time in it, which is not quite energy-efficient.
However, if the tick has not been stopped yet and the governor is
about to select a shallow idle state for the CPU even though the idle
duration predicted by it is above the tick boundary, it should be
fine to wake up the CPU early, so the tick can be retained then and
the governor will have a chance to select a deeper state when it runs
next time.
[Note that when this really happens, it will make the idle duration
predictor believe that the CPU might be idle longer than predicted,
which will make it more likely to predict longer idle durations going
forward, but that will also cause deeper idle states to be selected
going forward, on average, which is what's needed here.]
Fixes: 87c9fe6ee4 (cpuidle: menu: Avoid selecting shallow states with stopped tick)
Reported-by: Leo Yan <leo.yan@linaro.org>
Cc: 4.17+ <stable@vger.kernel.org> # 4.17+: 5ef499cd57 (cpuidle: menu: Handle ...)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Commit 87c9fe6ee4 (cpuidle: menu: Avoid selecting shallow states
with stopped tick) missed the case when the target residencies of
deep idle states of CPUs are above the tick boundary which may cause
the CPU to get stuck in a shallow idle state for a long time.
Say there are two CPU idle states available: one shallow, with the
target residency much below the tick boundary and one deep, with
the target residency significantly above the tick boundary. In
that case, if the tick has been stopped already and the expected
next timer event is relatively far in the future, the governor will
assume the idle duration to be equal to TICK_USEC and it will select
the idle state for the CPU accordingly. However, that will cause the
shallow state to be selected even though it would have been more
energy-efficient to select the deep one.
To address this issue, modify the governor to always use the time
till the closest timer event instead of the predicted idle duration
if the latter is less than the tick period length and the tick has
been stopped already. Also make it extend the search for a matching
idle state if the tick is stopped to avoid settling on a shallow
state if deep states with target residencies above the tick period
length are available.
In addition, make it always indicate that the tick should be stopped
if it has been stopped already for consistency.
Fixes: 87c9fe6ee4 (cpuidle: menu: Avoid selecting shallow states with stopped tick)
Reported-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: 4.17+ <stable@vger.kernel.org> # 4.17+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
The comment to explain why the menu governor uses idle state 1
instead of idle state 0 as the first one sometimes is stale (among
other things it mentions a user setting not present any more),
so update it.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
There is some code duplication related to the PM QoS handling between
the existing cpuidle governors, so move that code to a common helper
function and call that from the governors.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
PM_QOS_RESUME_LATENCY_NO_CONSTRAINT is defined as the 32-bit integer
maximum, so it is not necessary to test the return value of
dev_pm_qos_raw_read_value() against it directly in the menu and
ladder cpuidle governors.
Drop these redundant checks.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
If the scheduler tick has been stopped already and the governor
selects a shallow idle state, the CPU can spend a long time in that
state if the selection is based on an inaccurate prediction of idle
time. That effect turns out to be relevant, so it needs to be
mitigated.
To that end, modify the menu governor to discard the result of the
idle time prediction if the tick is stopped and the predicted idle
time is less than the tick period length, unless the tick timer is
going to expire soon.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
