android-mainline-tracking branch @ 4.18
ANDROID: Add hold functionality to schedtune CPU boost
When tasks come and go from a runqueue quickly, this can lead to boost
being applied and removed quickly which sometimes means we cannot raise
the CPU frequency again when we need to (due to the rate limit on
frequency updates). This has proved to be a particular issue for RT tasks
and alternative methods have been used in the past to work around it.
This is an attempt to solve the issue for all task classes and cpufreq
governors by introducing a generic mechanism in schedtune to retain
the max boost level from task enqueue for a minimum period - defined
here as 50ms. This timeout was determined experimentally and is not
configurable.
A sched_feat guards the application of this to tasks - in the default
configuration, task boosting only applied to tasks which have RT
policy. Change SCHEDTUNE_BOOST_HOLD_ALL to true to apply it to all
tasks regardless of class.
It works like so:
Every task enqueue (in an allowed class) stores a cpu-local timestamp.
If the task is not a member of an allowed class (all or RT depending
upon feature selection), the timestamp is not updated.
The boost group will stay active regardless of tasks present until
50ms beyond the last timestamp stored. We also store the timestamp
of the active boost group to avoid unneccesarily revisiting the boost
groups when checking CPU boost level.
If the timestamp is more than 50ms in the past when we check boost then
we re-evaluate the boost groups for that CPU, taking into account the
timestamps associated with each group.
Idea based on rt-boost-retention patches from Joel.
Change-Id: I52cc2d2e82d1c5aa03550378c8836764f41630c1
Suggested-by: Joel Fernandes <joelaf@google.com>
Reviewed-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
[forward ported from android-4.9-eas-dev proposal]
(cherry picked from commit a485e8b7bf8e95759e600396feeb7bfb400b6e46)
[ - Trivial cherry-pick conflicts in include/trace/events/sched.h ]
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
3 files changed
