[PATCH 0/3] sched/tick: Decouple sched_tick() from HZ

[Qais Yousef]

Previous attempt to make HZ 1000 the default [1] to help with scheduler
responsiveness didn't get merged. But maybe for the best, as I think this idea
of decoupling sched_tick() from HZ makes more sense. We shouldn't need to make
a choice between how often timers should trigger vs how often should the
scheduler update its stats/take decisions.

With HRTICK now is default on, preemption checks are less of problem. But tasks
could need to migrate (specifically on HMP systems) and frequencies could need
updating for solo long running tasks.

The conversion is half complete. We need to invent a new jiffy (piffy?) and
move existing load balancing logic (and potentially other users if they want
to) to speed them up. BUT, with push load balancer patches circulating around,
I am not sure it is worth while or desired to speed it since we have a better
faster mechanism to keep the system balanced without the need for the 'heavy
handed' full load balance to trigger. The push lb can benefit from this ptick
too to ensure more responsiveness.

[1] https://lore.kernel.org/lkml/20250226000810.459547-1-qyousef@xxxxxxxxxxx/

Qais Yousef (3):
  sched/tick: Decouple sched_tick() from HZ
  sched/tick: Move TICK_NSEC users to PTICK_NSEC
  sched/tick: Turn on PTICK by default

 kernel/sched/clock.c             |  4 +-
 kernel/sched/core.c              | 78 +++++++++++++++++++++++++++++---
 kernel/sched/cpufreq_schedutil.c |  2 +-
 kernel/sched/fair.c              |  6 +--
 kernel/sched/features.h          |  8 ++++
 kernel/sched/sched.h             |  7 +++
 6 files changed, 93 insertions(+), 12 deletions(-)

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2.34.1