On Mon, 8 Jan 2024 at 17:35, Dietmar Eggemann [off-list ref] wrote:

On 08/01/2024 14:48, Vincent Guittot wrote:

quoted

Provide to the scheduler a feedback about the temporary max available
capacity. Unlike arch_update_thermal_pressure, this doesn't need to be
filtered as the pressure will happen for dozens ms or more.

Is this then related to the 'medium pace system pressure' you mentioned
in your OSPM '23 talk?

quoted

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 drivers/cpufreq/cpufreq.c | 36 ++++++++++++++++++++++++++++++++++++
 include/linux/cpufreq.h   | 10 ++++++++++
 2 files changed, 46 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 44db4f59c4cc..fa2e2ea26f7f 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c

@@ -2563,6 +2563,40 @@ int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu)
 }
 EXPORT_SYMBOL(cpufreq_get_policy);

+DEFINE_PER_CPU(unsigned long, cpufreq_pressure);
+
+/**
+ * cpufreq_update_pressure() - Update cpufreq pressure for CPUs
+ * @policy: cpufreq policy of the CPUs.
+ *
+ * Update the value of cpufreq pressure for all @cpus in the policy.
+ */
+static void cpufreq_update_pressure(struct cpufreq_policy *policy)
+{
+     unsigned long max_capacity, capped_freq, pressure;
+     u32 max_freq;
+     int cpu;
+
+     /*
+      * Handle properly the boost frequencies, which should simply clean
+      * the thermal pressure value.

               ^^^^^^^
IMHO, this is a copy & paste error from topology_update_thermal_pressure()?

quoted

+      */
+     if (max_freq <= capped_freq) {

max_freq seems to be uninitialized.

argh yes, I made crap while cleaning up
both max_freq and capped_freq are uninitialized

quoted

+             pressure = 0;

Is this x86 (turbo boost) specific? IMHO at arm we follow this max freq
(including boost) relates to 1024 in capacity? Or haven't we made this
discussion yet?

This is not x86 specific. We can have capped_freq > max_freq on Arm too

Also this bypass all calculation below when max_freq == capped_freq
which is the most common case

quoted

+     } else {
+             cpu = cpumask_first(policy->related_cpus);
+             max_capacity = arch_scale_cpu_capacity(cpu);
+             capped_freq = policy->max;
+             max_freq = arch_scale_freq_ref(cpu);
+
+             pressure = max_capacity -
+                        mult_frac(max_capacity, capped_freq, max_freq);
+     }
+
+     for_each_cpu(cpu, policy->related_cpus)
+             WRITE_ONCE(per_cpu(cpufreq_pressure, cpu), pressure);
+}
+

[...]