Re: [PATCH v2 0/2] CPPC: reduce FFH feedback-counter sampling skew on arm64
Will Deacon <[email protected]>
| Newsgroups | org.kernel.vger.linux-acpi,dev.linux.lists.acpica-devel,org.infradead.lists.linux-arm-kernel,org.kernel.vger.linux-kernel |
|---|---|
| Message-ID | <[email protected]> |
On Wed, 08 Jul 2026 16:28:16 +0800, Pengjie Zhang wrote:
> The legacy CPPC feedback-counter path reads the delivered and reference
> performance counters separately.
>
> On arm64 systems using AMU-backed CPPC FFH counters, each FFH read is
> served through a cross-CPU counter read helper. Reading the counters
> separately therefore widens the sampling window between them and can
> skew the delivered/reference ratio used by cpuinfo_cur_freq. Under heavy
> load, the skew is observable as transient values that may exceed the
> platform maximum, as discussed in [1] and [2].
>
> [...]
Applied to arm64 (for-next/acpi), thanks!
[1/2] ACPI: CPPC: add paired FFH feedback-counter read hook
https://git.kernel.org/arm64/c/9aa7df520523
[2/2] arm64: topology: read CPPC FFH feedback counters in one operation
https://git.kernel.org/arm64/c/42971d5329d9
Cheers,
--
Will
https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev