Subject: Re: [PATCH] cpufreq: cppc: discard out-of-range delivered_perf samples

From: Breno Leitao <[email-masked]>
Date: Tue, 5 May 2026 05:52:21 -0700

Hello Jeremy,

On Fri, May 01, 2026 at 12:41:45PM -0500, Jeremy Linton wrote:
> A little jitter over, is probably expected. If that is what is happening
> then clamping to highest_perf makes sense instead.

Based on my analysis of the code, interrupts appear to remain enabled
during the delay, which could introduce significant jitter if an IRQ
fires during that window.

I'd be interested in testing this under an IRQ storm to quantify the
actual impact on the measurements.

> But then, this is really
> a sampling problem so does it go away if you double the udelay slightly.
> Maybe the udelay value should be proportional to the reference_perf value?

That's a reasonable approach. What would you suggest for the
implementation?

I considered making it a kernel or module parameter, but I'm not certain
that's the best solution, since the "user" might not know what to
set/use.

Thanks for your review,
--breno