Re: [PATCH v11 0/8] timers: Exclude isolated cpus from timer migration

["John B. Wyatt IV" <jwyatt@redhat.com>]

On Fri, Aug 08, 2025 at 06:01:34PM +0200, Gabriele Monaco wrote:
> The timer migration mechanism allows active CPUs to pull timers from
> idle ones to improve the overall idle time. This is however undesired
> when CPU intensive workloads run on isolated cores, as the algorithm
> would move the timers from housekeeping to isolated cores, negatively
> affecting the isolation.
> 
> Exclude isolated cores from the timer migration algorithm, extend the
> concept of unavailable cores, currently used for offline ones, to
> isolated ones:
> * A core is unavailable if isolated or offline;
> * A core is available if non isolated and online;

Hello Gabriele,

I tested your v11 patchset against 6.17-rc1-rt1 to see if it was the same issue with rtla-onoise getting latencies in the 20,000-40000 us on RHEL 10.2. It seems to have resolved the issue. Adding my tested-by tags and test results.

rtla osnoise top -c 1 -e sched:sched_switch -s 20 -T 1 -t -d 30m -q

CPU Period       Runtime        Noise  % CPU Aval   Max Noise   Max Single          HW          NMI          IRQ      Softirq       Thread
  1 #1799     1799000003      3382675    99.81196        2840            9        1578            0      1799012            0        24369

Tested-by: John B. Wyatt IV <jwyatt@redhat.com>
Tested-by: John B. Wyatt IV <sageofredondo@gmail.com>

-- 
Sincerely,
John Wyatt
Software Engineer, Core Kernel
Red Hat