Re: [PATCH] sched/topology: Avoid spurious asymmetry from CPU capacity noise

[Christian Loehle]

On 3/24/26 07:39, Vincent Guittot wrote:
> On Tue, 24 Mar 2026 at 01:55, Andrea Righi <arighi@xxxxxxxxxx> wrote:
>>
>> On some platforms, the firmware may expose per-CPU performance
>> differences (e.g., via ACPI CPPC highest_perf) even when the system is
>> effectively symmetric. These small variations, typically due to silicon
>> binning, are reflected in arch_scale_cpu_capacity() and end up being
>> interpreted as real capacity asymmetry.
>>
>> As a result, the scheduler incorrectly enables SD_ASYM_CPUCAPACITY,
>> triggering asymmetry-specific behaviors, even though all CPUs have
>> comparable performance.
>>
>> Prevent this by treating CPU capacities within 20% of the maximum value
> 
> 20% is a bit high, my snapdragon rb5 has a mid CPU with a capacity of
> 871 but we still want to keep them different
> 
> Why would 5% not be enough?

I've also used 5%, or rather the existing capacity_greater() macro.

>[snip]