[RFC PATCH v2 0/2] sched/fair migration reduction features

[Mathieu Desnoyers]

Hi,

This series introduces two new scheduler features: UTIL_FITS_CAPACITY
and SELECT_BIAS_PREV. When used together, they achieve a 41% speedup of
a hackbench workload which leaves some idle CPU time on a 192-core AMD
EPYC.

The main metrics which are significantly improved are:

- cpu-migrations are reduced by 80%,
- CPU utilization is increased by 17%.

Feedback is welcome. I am especially interested to learn whether this
series has positive or detrimental effects on performance of other
workloads.

The main changes since v1 are to take into account feedback from Chen Yu
and keep a 20% margin of unused utilization in the capacity fit, and use
scale_rt_capacity() which is more precise.

Thanks,

Mathieu

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Swapnil Sapkal <Swapnil.Sapkal@xxxxxxx>
Cc: Aaron Lu <aaron.lu@xxxxxxxxx>
Cc: Chen Yu <yu.c.chen@xxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxx>
Cc: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Cc: Gautham R . Shenoy <gautham.shenoy@xxxxxxx>
Cc: x86@xxxxxxxxxx

Mathieu Desnoyers (2):
  sched/fair: Introduce UTIL_FITS_CAPACITY feature (v2)
  sched/fair: Introduce SELECT_BIAS_PREV to reduce migrations

 kernel/sched/fair.c     | 68 ++++++++++++++++++++++++++++++++++++-----
 kernel/sched/features.h | 12 ++++++++
 kernel/sched/sched.h    |  5 +++
 3 files changed, 77 insertions(+), 8 deletions(-)

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2.39.2