linux-kernel - Re: [PATCH v1] x86/sched: Print debug messages on hybrid asym capacity changes

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Message-ID: <CAJZ5v0hS2+a4HsWQbhg5XCWph+tGMDnPy5DHXJnFCd8WMW5tqQ@mail.gmail.com>
Date: Wed, 9 Jul 2025 14:02:47 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, x86 Maintainers <x86@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>, 
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH v1] x86/sched: Print debug messages on hybrid asym
 capacity changes

On Wed, Jul 9, 2025 at 1:46 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Jul 09, 2025 at 12:47:17PM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Subject: [PATCH v1] x86/sched: Print debug messages on hybrid asym capacity changes
> >
> > Make arch_set_cpu_capacity() print a debug message including the
> > capacity and maximum frequency ratio used in scale-invariant utilization
> > computations for a given CPU and in capacity-aware scheduling (CAS) or
> > energy-aware scheduling (EAS).
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >  arch/x86/kernel/cpu/aperfmperf.c |    4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > --- a/arch/x86/kernel/cpu/aperfmperf.c
> > +++ b/arch/x86/kernel/cpu/aperfmperf.c
> > @@ -416,6 +416,10 @@
> >                          div_u64(cap << SCHED_CAPACITY_SHIFT, max_cap));
> >               WRITE_ONCE(per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio,
> >                          div_u64(cap_freq << SCHED_CAPACITY_SHIFT, base_freq));
> > +
> > +             pr_debug("CPU%d: capacity = %lu, freq_ratio = %lu\n", cpu,
> > +                      per_cpu_ptr(arch_cpu_scale, cpu)->capacity,
> > +                      per_cpu_ptr(arch_cpu_scale, cpu)->freq_ratio);
> >       } else {
> >               WARN_ONCE(1, "Hybrid CPU capacity scaling not enabled");
> >       }
>
> There's already a printk in the calling function
> hybrid_set_cpu_capacity(), so now we get _2_ prints per CPU. That's a
> bit excessive, no?

Yeah, fair enough.

> Also, should this print be conditional on sched_debug_verbose?

It might, but it is dynamic debug anyway.