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Subject[PATCH v2 0/9] Fix relationship between uclamp and fits_capacity()
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Relationship between uclamp and fits_capacity() is currently broken. Mostly due
to how uclamp should interact with migration margin and capacity pressure. But
also due not all users were converted to consider uclamp before calling
fits_capacity(). Namely cpu_overutilized().

The meat of the series is patch 1 where we introduce a new function,
util_fits_cpu(), that takes uclamp into account. The new function should
replace all call sits to fits_capacity(), which what subsequent patches do.
Except for patch 7 where we fix handling of early exit condition in
find_energy_efficient_cpu(AKA feec()) that must be uclamp aware too.

util_fits_cpu() will revert back to a simple call to fits_capacity() if uclamp
is not being used on the system.

Last two patches still need testing and verification, but they address the
various thermal handling issues raised in v1. We can re-order the patches, but
added at the end to facilitate review at this stage. Hope the approach and the
logic make sense.

I'll be on holidays, so if I don't respond to review comments fast enough,
apologies in advance.

Changes in v2:

* use uclamp_rq_is_idle() in uclamp_rq_util_with() (Xuewen)

* Simplify logic in update_sg_wakeup_stats() when converting
task_fits_cpu() (Vincent)

* Better handling of thermal pressure (Vincent)

- We consider thermal pressure for uclamp_min in patch 1
- 2 new patches to handle capacity inversion which improves handling
when:

+ There're multiple big cpus on separate perf domains.
+ A task is boosted by uclamp_min and inspite of thermal
pressure, the big cpu is still the best placement.

e.g: p0->util_avg = 300, p0->uclamp_min = 1024

This task should stay on big CPU until thermal pressure is in
capacity inversion.

v1 discussion: https://lore.kernel.org/lkml/20220629194632.1117723-1-qais.yousef@arm.com/

Thanks for all reviewers on v1!


Qais Yousef (9):
sched/uclamp: Fix relationship between uclamp and migration margin
sched/uclamp: Make task_fits_capacity() use util_fits_cpu()
sched/uclamp: Fix fits_capacity() check in feec()
sched/uclamp: Make select_idle_capacity() use util_fits_cpu()
sched/uclamp: Make asym_fits_capacity() use util_fits_cpu()
sched/uclamp: Make cpu_overutilized() use util_fits_cpu()
sched/uclamp: Cater for uclamp in find_energy_efficient_cpu()'s early
exit condition
sched/fair: Detect capacity inversion
sched/fair: Consider capacity inversion in util_fits_cpu()

kernel/sched/core.c | 10 +-
kernel/sched/fair.c | 290 ++++++++++++++++++++++++++++++++++++++-----
kernel/sched/sched.h | 70 ++++++++++-
3 files changed, 329 insertions(+), 41 deletions(-)

--
2.25.1

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