[PATCH v7 0/4] sched/psi: Allow unprivileged PSI polling

[Domenico Cerasuolo]

PSI offers 2 mechanisms to get information about a specific resource
pressure. One is reading from /proc/pressure/<resource>, which gives
average pressures aggregated every 2s. The other is creating a pollable
fd for a specific resource and cgroup.

The trigger creation requires CAP_SYS_RESOURCE, and gives the
possibility to pick specific time window and threshold, spawing an RT
thread to aggregate the data.

Systemd would like to provide containers the option to monitor pressure
on their own cgroup and sub-cgroups. For example, if systemd launches a
container that itself then launches services, the container should have
the ability to poll() for pressure in individual services. But neither
the container nor the services are privileged.

The series is implemented in 4 steps in order to reduce the noise of
the change.

V7:
- fix code style in psi trigger create/destroy aggregators paths

V6:
- fix trigger creation logic now using proper locks

V5:
- few suggested code style changes in psi.c and psy_types.h
- fix trigger destruction logic now using proper locks

V4:
- fixed psi_open leftover usage in IRQ accounting (patch 4/4)

V3:
- restored renaming patch (#2 of 4) as suggested in review
- rebased #3 and #4 on the renaming commit

V2:
- removed renaming patch (previous 2/4) and applied suggested solution
- changed update_triggers side effect removal as suggested in review
- rebased core patch on other V2 changes

Domenico Cerasuolo (4):
  sched/psi: rearrange polling code in preparation
  sched/psi: rename existing poll members in preparation
  sched/psi: extract update_triggers side effect
  sched/psi: allow unprivileged polling of N*2s period

 Documentation/accounting/psi.rst |   4 +
 include/linux/psi.h              |   2 +-
 include/linux/psi_types.h        |  43 +--
 kernel/cgroup/cgroup.c           |   2 +-
 kernel/sched/psi.c               | 443 +++++++++++++++++--------------
 5 files changed, 276 insertions(+), 218 deletions(-)

-- 
2.34.1