On Thu, 2021-04-29 at 09:12 +0200, Vincent Guittot wrote:

Hi Scott,

On Thu, 29 Apr 2021 at 01:28, Scott Wood [off-list ref] wrote:

quoted

These patches mitigate latency caused by newidle_balance() on large
systems when PREEMPT_RT is enabled, by enabling interrupts when the lock
is dropped, and exiting early at various points if an RT task is
runnable
on the current CPU.

On a system with 128 CPUs, these patches dropped latency (as measured by
a 12 hour rteval run) from 1045us to 317us (when applied to
5.12.0-rc3-rt3).

The patch below has been queued for v5.13 and removed the update of
blocked load what seemed to be the major reason for long preempt/irq
off during newly idle balance:
https://lore.kernel.org/lkml/20210224133007.28644-1-vincent.guittot@linaro.org/ (local)

I would be curious to see how it impacts your cases

I still get 1000+ ms latencies with those patches applied.

-Scott