Re: [PATCH] cpufreq: schedutil: Don't skip freq update when limits change

Viresh Kumar
2019-07-26T06:57:45Z

On 25-07-19, 08:20, Doug Smythies wrote:
> I tried the patch ("patch2"). It did not fix the issue.
>
> To summarize, all kernel 5.2 based, all intel_cpufreq driver and schedutil governor:
>
> Test: Does a busy system respond to maximum CPU clock frequency reduction?
>
> stock, unaltered: No.
> revert ecd2884291261e3fddbc7651ee11a20d596bb514: Yes
> viresh patch: No.
> fast_switch edit: No.
> viresh patch2: No.

Hmm, so I tried to reproduce your setup on my ARM board.
- booted only with CPU0 so I hit the sugov_update_single() routine
- And applied below diff to make CPU look permanently busy:

-------------------------8<-------------------------
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 2f382b0959e5..afb47490e5dc 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -121,6 +121,7 @@ static void sugov_fast_switch(struct sugov_policy *sg_policy, u64 time,
if (!sugov_update_next_freq(sg_policy, time, next_freq))
return;

+ pr_info("%s: %d: %u\n", __func__, __LINE__, freq);
next_freq = cpufreq_driver_fast_switch(policy, next_freq);
if (!next_freq)
return;
@@ -424,14 +425,10 @@ static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
#ifdef CONFIG_NO_HZ_COMMON
static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu)
{
- unsigned long idle_calls = tick_nohz_get_idle_calls_cpu(sg_cpu->cpu);
- bool ret = idle_calls == sg_cpu->saved_idle_calls;
-
- sg_cpu->saved_idle_calls = idle_calls;
- return ret;
+ return true;
}
#else
-static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
+static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return true; }
#endif /* CONFIG_NO_HZ_COMMON */

/*
@@ -565,6 +562,7 @@ static void sugov_work(struct kthread_work *work)
sg_policy->work_in_progress = false;
raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags);

+ pr_info("%s: %d: %u\n", __func__, __LINE__, freq);
mutex_lock(&sg_policy->work_lock);
__cpufreq_driver_target(sg_policy->policy, freq, CPUFREQ_RELATION_L);
mutex_unlock(&sg_policy->work_lock);

-------------------------8<-------------------------

Now, the frequency never gets down and so gets set to the maximum
possible after a bit.

- Then I did:

echo <any-low-freq-value> > /sys/devices/system/cpu/cpufreq/policy0/scaling_max_freq

Without my patch applied:
The print never gets printed and so frequency doesn't go down.

With my patch applied:
The print gets printed immediately from sugov_work() and so
the frequency reduces.

Can you try with this diff along with my Patch2 ? I suspect there may
be something wrong with the intel_cpufreq driver as the patch fixes
the only path we have in the schedutil governor which takes busyness
of a CPU into account.

--
viresh