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[v1,0/5] cpufreq/sched: Improve synchronization of policy limits updates with schedutil

Message ID 3364921.aeNJFYEL58@rjwysocki.net
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Series cpufreq/sched: Improve synchronization of policy limits updates with schedutil | expand

Message

Rafael J. Wysocki April 14, 2025, 8:39 p.m. UTC 
Hi Everyone,

This series of patches has been inspired by the discussion following a bug
report regarding the patch at

https://lore.kernel.org/lkml/20241212015734.41241-2-sultan@kerneltoast.com/

and its attempted unsuccessful resolution:

https://lore.kernel.org/linux-pm/20250410024439.20859-1-sultan@kerneltoast.com/

which basically leads to the conclusion that cpufreq policy limits updates are
not sufficiently synchronized with the scheditil governor, especially in the
fast switching case in which running the driver callback is the only way to
make the new policy limits take effect.

The purpose of this series is to address this concern.

Patch [1/5] is a fix for the issue introduced by the patch linked above (please
see the patch changelog for details), for 6.15-rc.  The remaining patches are
for 6.16.

Patch [2/5] adds memory barriers in two places in schedutil along with some
WRITE_ONCE()/READ_ONCE() annotations to ensure that policy limits updates will
not be missed due to reordering of instructions.

Patch [3/5] is a preparatory function rename with no functional impact.

Patch [4/5] updates the cpufreq core to avoid situations in which
cpufreq_driver_resolve_freq(), called by schedutil, may see intermediate
values of policy->min and policy->max and makes that function address the
unlikely case in which it may see policy->min > policy->max.

Patch [5/5] cleans up the code after the previous changes.

Please see individual patch changelogs for details.

Thanks!