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

[Mete Durlu]

Hi Shrikanth,

> > > 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.
>
> Sorry, i don't follow.
>
> Did you mean pin to preferred CPUs? Why would anyone want to run their
> workload only on non-preferred CPUs? By definition, they are not meant to
> be used as much as possible. and It is benchmarking.

I think they want to prevent anything else *besides* their workload
from running on these CPUs by marking them non-preferred and then
pinning their workload there.
Sort of like like dynamically configurable isolated CPUs.

IMO this fits 1-1 with what Yury is describing with this patchset.

Thanks,
-Mete