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

Peter Zijlstra
2026-01-29T09:19:55Z

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.)

> -------------------------------------------------------------------------
>
> 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.