Re: [PATCH v2 00/13] sched/fair/schedutil: Better manage system response time

[Tom Gebhardt]

Hi Qais,

I tested your v2 12/13 (sched/fair: Call update_util_est() after
dequeue_entities()) and RFC 13/13 (sched/pelt: Always allow load updates)
on ARM (Raspberry Pi 5, Cortex-A76, 4-core), combined with Peter
Zijlstra's ttwu series (rebased to 7.0.y by marioroy).

Both patches applied cleanly on top of rpi-7.0.y + 10 ttwu patches
without conflicts.

Results using stress-ng 0.15.06 pipe stressor (4 workers, 20s):

  Kernel                              Clock      pipe bogo ops/s   D vs. 6.6
  ----------------------------------  ---------  ----------------  ----------
  6.6.78-v8-16k+                      2800 MHz        2 487 746    +/-0% (ref)
  7.0.0-v8-16k+ stock                 2400 MHz        1 694 011    -31.9%
  7.0.0-v8-16k+ stock                 2800 MHz        1 851 567    -25.6%
  7.0.0 + ttwu only (10 patches)      2400 MHz        1 836 006    -26.2%
  7.0.0 + ttwu only (10 patches)      2800 MHz        1 934 076    -22.3%
  7.0.0 + ttwu + your 2 Qais patches  2400 MHz        1 996 002    -19.8%
  7.0.0 + ttwu + your 2 Qais patches  2800 MHz        2 342 144     -5.9%

The ttwu-only set recovers ~3-4% of the regression on ARM. Adding your
two patches brings a much larger improvement -- especially under
overclocking, where the combined set recovers roughly 94% of the 6.6
baseline. The remaining ~6% gap may be related to ARM-specific
DELAY_DEQUEUE interactions.

Device: Raspberry Pi 5 (8 GB, C1-stepping), Bookworm arm64, rpi-7.0.y.
Background: https://github.com/raspberrypi/linux/issues/7308

Thanks for the series -- the ARM results look very promising.

Tom