Re: [PATCH v3 1/2] arm64: topology: fix arch_freq_get_on_cpu() overflow above 4.19 GHz

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 10.09.26 08:34, Oleg Keri wrote:

[...]

> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index d28438f8b83f..0eca321ff113 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -245,8 +245,7 @@ int arch_freq_get_on_cpu(int cpu)
>  	 * (see amu_scale_freq_tick for details)
>  	 */
>  	scale = arch_scale_freq_capacity(cpu);
> -	freq = scale * arch_scale_freq_ref(cpu);
> -	freq >>= SCHED_CAPACITY_SHIFT;
> +	freq = (scale * arch_scale_freq_ref(cpu)) >> SCHED_CAPACITY_SHIFT;
>  	return freq;
>  }

In task scheduler code we use cap_scale(v, s) for CPU capacity related
scaling.

We could move its definition from private task scheduler include file
kernel/sched/sched.h to include/linux/topology.h to be able to use it
also outside the task scheduler?

Only compile tested on arm64 and x86.

-->8--

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 0eca321ff113..180a7aa97752 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -186,7 +186,6 @@ int arch_freq_get_on_cpu(int cpu)
      struct amu_cntr_sample *amu_sample;
      unsigned int start_cpu = cpu;
      unsigned long last_update;
-     unsigned int freq = 0;
      u64 scale;

      if (!amu_fie_cpu_supported(cpu) || !arch_scale_freq_ref(cpu))
@@ -245,8 +244,7 @@ int arch_freq_get_on_cpu(int cpu)
      * (see amu_scale_freq_tick for details)
      */
      scale = arch_scale_freq_capacity(cpu);
-     freq = (scale * arch_scale_freq_ref(cpu)) >> SCHED_CAPACITY_SHIFT;
-     return freq;
+     return cap_scale(arch_scale_freq_ref(cpu), scale);
 }

 static void amu_fie_setup(const struct cpumask *cpus)
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 709a2dcf4c73..0a4ee12a98d5 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -351,4 +351,6 @@ static inline unsigned long
topology_get_cpu_scale(int cpu)

 void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity);

+#define cap_scale(v, s)               ((v)*(s) >> SCHED_CAPACITY_SHIFT)
+
 #endif /* _LINUX_TOPOLOGY_H */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 6c3ad70e58b8..45796fccdc84 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -236,8 +236,6 @@ static inline int task_has_dl_policy(struct
task_struct *p)
        return dl_policy(p->policy);
 }

-#define cap_scale(v, s)               ((v)*(s) >> SCHED_CAPACITY_SHIFT)
-
 static inline void update_avg(u64 *avg, u64 sample)
 {
        s64 diff = sample - *avg;