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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%) |
Bug: 258723112
Change-Id: Ifea46051fb4b0554349aa50145130e38efa5f163
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>
(cherry picked from commit 9ce0f7c4bc)
[Build error due to different signature of sched_cpu_util()]
Signed-off-by: Qais Yousef <qyousef@google.com>
How do I submit patches to Android Common Kernels
-
BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
EXPORT_SYMBOL_GPL()require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export. - When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not not a persuasive case.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
-
LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.
Common Kernel patch requirements
- All patches must conform to the Linux kernel coding standards and pass
scripts/checkpatch.pl - Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
- If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch:
UPSTREAM:,BACKPORT:,FROMGIT:,FROMLIST:, orANDROID:. - All patches must have a
Change-Id:tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html) - If an Android bug has been assigned, there must be a
Bug:tag. - All patches must have a
Signed-off-by:tag by the author and the submitter
Additional requirements are listed below based on patch type
Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:
- If the patch is a cherry-pick from Linux mainline with no changes at all
- tag the patch subject with
UPSTREAM:. - add upstream commit information with a
(cherry picked from commit ...)line - Example:
- if the upstream commit message is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
UPSTREAM: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch requires any changes from the upstream version, tag the patch with
BACKPORT:instead ofUPSTREAM:.- use the same tags as
UPSTREAM: - add comments about the changes under the
(cherry picked from commit ...)line - Example:
- use the same tags as
BACKPORT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
[joe: Resolved minor conflict in drivers/foo/bar.c ]
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for other backports: FROMGIT:, FROMLIST:,
- If the patch has been merged into an upstream maintainer tree, but has not yet
been merged into Linux mainline
- tag the patch subject with
FROMGIT: - add info on where the patch came from as
(cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't uselinux-nextfor example). - if changes were required, use
BACKPORT: FROMGIT: - Example:
- if the commit message in the maintainer tree is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
FROMGIT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
(cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch has been submitted to LKML, but not accepted into any maintainer tree
- tag the patch subject with
FROMLIST: - add a
Link:tag with a link to the submittal on lore.kernel.org - add a
Bug:tag with the Android bug (required for patches not accepted into a maintainer tree) - if changes were required, use
BACKPORT: FROMLIST: - Example:
- tag the patch subject with
FROMLIST: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for Android-specific patches: ANDROID:
- If the patch is fixing a bug to Android-specific code
- tag the patch subject with
ANDROID: - add a
Fixes:tag that cites the patch with the bug - Example:
- tag the patch subject with
ANDROID: fix android-specific bug in foobar.c
This is the detailed description of the important fix
Fixes: 1234abcd2468 ("foobar: add cool feature")
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch is a new feature
- tag the patch subject with
ANDROID: - add a
Bug:tag with the Android bug (required for android-specific features)
- tag the patch subject with