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

Mohamed Abuelfotoh, Hazem
2026-01-28T15:48:32Z

On 27/01/2026 08:44, Peter Zijlstra wrote:
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> On Sun, Jan 25, 2026 at 12:22:21PM +0000, Mohamed Abuelfotoh, Hazem wrote:
>> I can confirm that we are seeing a 4-11% performance regression in v6.12.66
>> on multiple benchmarks running on c7a.4xlarge AWS EC2 instances that are
>> powered by AMD EPYC 9R14-series CPU (code-named Genoa) and c7i.4xlarge which
>> is powered by 4th-Generation Intel Xeon Scalable processor (code-named
>> Sapphire Rapids).
>
> For those not speaking Amazon; what actual system setup is that Xeon? Is
> that single socket or multi-socket?
>
> Going by the name, the 4x would suggest a quad-socket Xeon, which are
> somewhat beastly, but if I google this 'c7i.4xlarge' identifier, I get a
> puny single socket 16cpu thing.
>
> What is it?

Hi Peter,

Apologize for the confusion, the "4x" is just an Amazon naming for EC2
instance sizing, basically number of CPUs & Memory and Network
Bandwidth. The naming has nothing to do with exact number of sockets
within the VM.

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

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c7a.4xlarge

CPU Model: AMD EPYC 9R14
Number of CPUs: 16
Memory: 32 GB
Number of sockets: 1