From f341dc4d934a69ffbe6c21e3609ee725790188f1 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Mon, 21 Sep 2026 21:12:00 +0200 Subject: [PATCH] cpufreq: intel_pstate: Fix max_freq fallback in cpufreq_update_pressure() After commit d2d5c129d07e ("cpufreq: Make cpufreq_update_pressure() fall back to cpuinfo.max_freq"), cpufreq pressure appears in the CPU load balancer unexpectedly in some cases in which it was not present before, leading to confusion and uncertainty. Clearly, the scheduler assumes that cpufreq pressure will not be set unless the capacity reference frequency of the CPU is known, and the commit mentioned above violates that assumption. However, in some cases the capacity reference frequency of the CPU is in fact known even though arch_scale_freq_ref() returns 0 and in those cases it should be possible to set cpufreq pressure as appropriate. For this purpose, introduce a new cpufreq driver callback returning the CPU capacity reference frequency, .scale_freq_ref(), and make cpufreq_update_pressure() invoke it, if present, instead of falling back to cpuinfo.max_freq unconditionally. Add that callback to the intel_pstate driver and make it return 0 unless the scale-invariant capacity of the given CPU has been explicitly set, in which cases its reference frequency is always cpuinfo.max_freq. Fixes: d2d5c129d07e ("cpufreq: Make cpufreq_update_pressure() fall back to cpuinfo.max_freq") Reported-by: Jianyong Wu Closes: https://lore.kernel.org/linux-pm/20260915065747.1671965-1-wujianyong@hygon.cn/ Tested-by: Jianyong Wu Signed-off-by: Rafael J. Wysocki Tested-by: Ricardo Neri # Intel hybrid parts Tested-by: Chen Yu [ rjw: Add READ_ONCE() around a capacity_perf read ] Link: https://patch.msgid.link/12975163.O9o76ZdvQC@rafael.j.wysocki Signed-off-by: Rafael J. Wysocki --- drivers/cpufreq/cpufreq.c | 4 ++-- drivers/cpufreq/intel_pstate.c | 10 ++++++++++ include/linux/cpufreq.h | 3 +++ 3 files changed, 15 insertions(+), 2 deletions(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 96515880b4ac..54dde8419bdc 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -2590,8 +2590,8 @@ static void cpufreq_update_pressure(struct cpufreq_policy *policy) cpu = cpumask_first(policy->related_cpus); max_freq = arch_scale_freq_ref(cpu); - if (!max_freq) - max_freq = policy->cpuinfo.max_freq; + if (!max_freq && cpufreq_driver->scale_freq_ref) + max_freq = cpufreq_driver->scale_freq_ref(policy); capped_freq = policy->max; diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index ceb340f7a110..17158cb25dd8 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -1135,6 +1135,14 @@ static bool hybrid_clear_max_perf_cpu(void) return ret; } +static unsigned int intel_pstate_scale_freq_ref(struct cpufreq_policy *policy) +{ + if (READ_ONCE(all_cpu_data[policy->cpu]->capacity_perf)) + return policy->cpuinfo.max_freq; + + return 0; +} + static void intel_pstate_update_freq_limits(struct cpudata *cpu) { int scaling = cpu->pstate.scaling; @@ -3088,6 +3096,7 @@ static struct cpufreq_driver intel_pstate = { .offline = intel_pstate_cpu_offline, .online = intel_pstate_cpu_online, .update_limits = intel_pstate_update_limits, + .scale_freq_ref = intel_pstate_scale_freq_ref, .name = "intel_pstate", }; @@ -3411,6 +3420,7 @@ static struct cpufreq_driver intel_cpufreq = { .suspend = intel_cpufreq_suspend, .resume = intel_pstate_resume, .update_limits = intel_pstate_update_limits, + .scale_freq_ref = intel_pstate_scale_freq_ref, .name = "intel_cpufreq", }; diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 35ce665edfd8..d3d0d9d02aa4 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -420,6 +420,9 @@ struct cpufreq_driver { /* Will be called after the driver is fully initialized */ void (*ready)(struct cpufreq_policy *policy); + /* Return the capacity reference frequency for policy. */ + unsigned int (*scale_freq_ref)(struct cpufreq_policy *policy); + struct freq_attr **attr; /* platform specific boost support code */