Re: [PATCH 4/4] sched/fair: Proportional newidle balance

Peter Zijlstra
2026-01-29T09:24:20Z

On Thu, Jan 29, 2026 at 10:19:37AM +0100, Peter Zijlstra wrote:
> On Wed, Jan 28, 2026 at 03:48:13PM +0000, Mohamed Abuelfotoh, Hazem wrote:
>
> > Below are the hardware specs for both c7i.4xlarge & c7a.4xlarge.
> >
> > c7i.4xlarge
> >
> > CPU Model: Intel(R) Xeon(R) Platinum 8488C
> > Number of CPUs: 16
> > Memory: 32 GB
> > Number of sockets: 1
>
> But the 8488C is a 56 core part, with 112 threads. So you're handing out
> 8 core partitions of that thing, for 7 such instances on one machine?
>
> (Also, calling anything 16 core with 32GB 'large' is laughable, that's
> laptop territory.)

Also, are you employing Intel-CAT on these partitions to separate the
L3s?

(Not immediately relevant I suppose, but I was curious)

> > -------------------------------------------------------------------------
> >
> > c7a.4xlarge
> >
> > CPU Model: AMD EPYC 9R14
> > Number of CPUs: 16
> > Memory: 32 GB
> > Number of sockets: 1
>
> And that 9r14 is a 96 core part, 12 CCDs, 8 cores each. So you're again
> handing out partitions of that.
>
>
>
> For both cases, are these partitions fixed? Specifically in the AMD case,
> are you handing out exactly 1 CCDs per partition?
>
> Because if so, I'm mighty confused by the results. 8 cores, 16 threads
> is exactly one CCD worth of Zen4 and should therefore be a single L3 and
> behave exactly like the Intel thing.
>
> Something is missing here.