[v3,0/4] PM: QoS: Restore DEV_PM_QOS_MIN/MAX_FREQUENCY

Message

Leonard Crestez Nov. 25, 2019, 4:42 p.m. UTC

Support for frequency limits in dev_pm_qos was removed when cpufreq was
switched to freq_qos, this series attempts to restore it by
reimplementing on top of freq_qos.

Discussion about removal is here:
https://lore.kernel.org/linux-pm/[e-mail]/T/#u

The cpufreq core switched away because it needs contraints at the level
of a "cpufreq_policy" which cover multiple cpus so dev_pm_qos coupling
to struct device was not useful. Cpufreq could only use dev_pm_qos by
implementing an additional layer of aggregation anyway.

However in the devfreq subsystem scaling is always performed on a per-device
basis so dev_pm_qos is a very good match. Support for dev_pm_qos in devfreq
core is here:

	https://patchwork.kernel.org/cover/11252409/

That series is RFC mostly because it needs these PM core patches.
Earlier versions got entangled in some locking cleanups but those are
not strictly necessary to get dev_pm_qos functionality.

In theory if freq_qos is extended to handle conflicting min/max values then
this sharing would be valuable. Right now freq_qos just ties two unrelated
pm_qos aggregations for min and max freq.

---
This is implemented by embeding a freq_qos_request inside dev_pm_qos_request:
the data field was already an union in order to deal with flag requests.

The internal freq_qos_apply is exported so that it can be called from
dev_pm_qos apply_constraints.

The dev_pm_qos_constraints_destroy function has no obvious equivalent in
freq_qos and the whole approach of "removing requests" is somewhat dubios:
request objects should be owned by consumers and the list of qos requests
should be empty when the target device is deleted.

Changes since v2:
* #define PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE FREQ_QOS_MAX_DEFAULT_VALUE
* #define FREQ_QOS_MAX_DEFAULT_VALUE S32_MAX (in new patch)
* Add initial kunit test for freq_qos, validating the MAX_DEFAULT_VALUE found
by Matthias.
Link to v2: https://patchwork.kernel.org/cover/11250413/

First two patches can be applied separated

Changes since v1:
* Don't rename or EXPORT_SYMBOL_GPL the freq_qos_apply function; just
drop the static marker.
Link to v1: https://patchwork.kernel.org/cover/11212887/

Leonard Crestez (4):
  PM / QoS: Initial kunit test
  PM / QOS: Redefine FREQ_QOS_MAX_DEFAULT_VALUE to S32_MAX
  PM / QoS: Reorder pm_qos/freq_qos/dev_pm_qos structs
  PM / QoS: Restore DEV_PM_QOS_MIN/MAX_FREQUENCY

 drivers/base/Kconfig          |   4 ++
 drivers/base/power/Makefile   |   1 +
 drivers/base/power/qos-test.c | 116 ++++++++++++++++++++++++++++++++++
 drivers/base/power/qos.c      |  69 ++++++++++++++++++--
 include/linux/pm_qos.h        |  86 ++++++++++++++-----------
 kernel/power/qos.c            |   4 +-
 6 files changed, 237 insertions(+), 43 deletions(-)
 create mode 100644 drivers/base/power/qos-test.c