Re: [PATCH RESEND] cpufreq: schedutil: Use idle_calls counter of the remote CPU

[Joel Fernandes]

Hi Rafael,

On 12/20/2017 06:45 AM, Rafael J. Wysocki wrote:
> On Tuesday, December 19, 2017 8:32:09 PM CET Joel Fernandes wrote:
>> On Tue, Dec 19, 2017 at 10:48 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>>> On Tue, Dec 19, 2017 at 09:47:12AM -0800, Joel Fernandes wrote:
>>>> Since the recent remote cpufreq callback work, its possible that a cpufreq
>>>> update is triggered from a remote CPU. For single policies however, the current
>>>> code uses the local CPU when trying to determine if the remote sg_cpu entered
>>>> idle or is busy. This is incorrect. To remedy this, compare with the nohz tick
>>>> idle_calls counter of the remote CPU.
>>>>
>>>> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
>>>> Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
>>>
>>> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
>>
>> Sweet!
> 
> OK, so any chance to get a Fixes: tag for the patch?

Sure. Please find an inline patch below with all acks and fixes tag. thanks!

---8<---
From: Joel Fernandes <joelaf@xxxxxxxxxx>
Subject: [PATCH] cpufreq: schedutil: Use idle_calls counter of the remote CPU

Since the recent remote cpufreq callback work, its possible that a cpufreq
update is triggered from a remote CPU. For single policies however, the current
code uses the local CPU when trying to determine if the remote sg_cpu entered
idle or is busy. This is incorrect. To remedy this, compare with the nohz tick
idle_calls counter of the remote CPU.

Fixes: 674e75411fc2 ("sched: cpufreq: Allow remote cpufreq callbacks")
Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
---
 include/linux/tick.h             |  1 +
 kernel/sched/cpufreq_schedutil.c |  2 +-
 kernel/time/tick-sched.c         | 13 +++++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index f442d1a42025..7cc35921218e 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -119,6 +119,7 @@ extern void tick_nohz_idle_exit(void);
 extern void tick_nohz_irq_exit(void);
 extern ktime_t tick_nohz_get_sleep_length(void);
 extern unsigned long tick_nohz_get_idle_calls(void);
+extern unsigned long tick_nohz_get_idle_calls_cpu(int cpu);
 extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
 extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
 #else /* !CONFIG_NO_HZ_COMMON */
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 2f52ec0f1539..d6717a3331a1 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -244,7 +244,7 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, unsigned long *util,
 #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();
+	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;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 99578f06c8d4..77555faf6fbc 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -985,6 +985,19 @@ ktime_t tick_nohz_get_sleep_length(void)
 	return ts->sleep_length;
 }
 
+/**
+ * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
+ * for a particular CPU.
+ *
+ * Called from the schedutil frequency scaling governor in scheduler context.
+ */
+unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
+{
+	struct tick_sched *ts = tick_get_tick_sched(cpu);
+
+	return ts->idle_calls;
+}
+
 /**
  * tick_nohz_get_idle_calls - return the current idle calls counter value
  *