Re: [PATCH v2 4/4] sched/rt: Split cpupri_vec->cpumask to per NUMA node to reduce contention

[Chen, Yu C]

Hello Prateek,

On 4/8/2026 11:06 AM, K Prateek Nayak wrote:
> Hello Tim,
>
> On 4/8/2026 2:05 AM, Tim Chen wrote:
> > > And regarding your other question about the calculation of arch_sbm_shift,
> > > I'm trying to understand why there is a subtraction of 1, should it be:
> > > -       arch_sbm_shift = x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN] - 1;
> > > +       arch_sbm_shift = x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN - 1];
> >
> > Perhaps something like
> >
> > 	arch_sbm_shift = min(sizeof(unsigned long),
> > 			     topology_get_domain_shift(TOPO_TILE_DOMAIN));
> >
> > to take care of both AMD system and the 64 bit leaf bitmask limit?
>
> Ack! But do we want to separate CPUs on same LLC domain across
> different cachelines in 64 CPU chunks or should we use the rest
> of the padding to represent them?

I just saw your email and I had the same question.

> I'm collecting some performance numbers to see if makes any
> difference under high contention but have you seen benefits of
> sharding the mask further when there are hundreds of CPU on the
> same LLC?

We haven't tried breaking it down further. One possible approach
is to partition it at L2 scope, the benefit of which may depend on
the workload.


thanks,
Chenyu