Re: [PATCH 0/6] sched: Expose writable interface for preferred CPUs mask

[Yury Norov <ynorov@nvidia.com>]

On Tue, Nov 10, 2026 at 04:15:31PM +1300, Maxim Kuvyrkov wrote:
> > On Nov 2, 2026, at 08:21, Yury Norov <ynorov@nvidia.com> wrote:
> > 
> > The preferred CPU mask currently lets the steal governor reduce vCPU
> > demand when physical CPUs are contended. This series adds manual control,
> > opening more use cases.
> > 
> > For example, setting CPUs aside for selected fair tasks at runtime while
> > steering other fair tasks toward the remaining CPUs.
> 
> Hi Yury,
> 
> I've been trying to do this with crutches in user-space for a long time.  Thanks for implementing this in the kernel, and with a convenient user interface.
> 
> > 
> > A user can mark a CPU non-preferred and pin a workload to it. Fair tasks
> > whose affinity includes preferred CPUs are steered away, while tasks
> > whose allowed CPUs contain no preferred CPU can still run there. The CPU
> > stays online, task affinity is preserved, and the selection can be
> > reversed without rebooting:
> > 
> >    # rmmod steal_governor
> >    # echo 0 > /sys/devices/system/cpu/cpu3/preferred
> >    # taskset -c 3 ./my_workload
> >    # echo 1 > /sys/devices/system/cpu/cpu3/preferred
> 
> My use-case (being a compiler optimization engineer) is to pin benchmarks to specific cores, and stop the system from using those cores even when the cores are idle.  This prevents L1/L2 cache pollution and makes performance numbers more stable.

Hi Maxim,

Thank you for the feedback.

I agree, this trick with pinning a workload to an non-preferred CPU
looks promising for benchmarking purposes, and probably for more.

I'm going to split this series to the cleanup and follow-up parts.
In the follow-up, I'll focus on this writable interface. I'll keep
you in CC there.

Thanks,
Yury