Re: [PATCH 2/4] x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF

[Len Brown]

On Tue, Jun 20, 2017 at 6:15 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Fri, 16 Jun 2017, Len Brown wrote:
>> +#include <linux/jiffies.h>
>> +#include <linux/math64.h>
>> +#include <linux/percpu.h>
>> +#include <linux/smp.h>
>> +
>> +struct aperfmperf_sample {
>> +     unsigned int khz;
>> +     unsigned long jiffies;
>> +     u64 aperf;
>> +     u64 mperf;
>
> Nit. Please write these in tabular fashion:
>         unsigned        int khz;
>         unsigned long   jiffies;
>         u64             aperf;
>         u64             mperf;

sure, no problem -- I agreed that looks better.

But it seems there is some inconsistency about this style nit --
even in this directory.  If there is consensus going forward,
would it make sense for coding-style.rst and checkpatch.pl
to squawk about this, so you don't have to?


>> +};
>> +
>> +static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
>> +
>> +/*
>> + * aperfmperf_snapshot_khz()
>> + * On the current CPU, snapshot APERF, MPERF, and jiffies
>> + * unless we already did it within 10ms
>> + * calculate kHz, save snapshot
>> + */
>> +static void aperfmperf_snapshot_khz(void *dummy)
>> +{
>> +     u64 aperf, aperf_delta;
>> +     u64 mperf, mperf_delta;
>> +     struct aperfmperf_sample *s = &get_cpu_var(samples);
>
> This is invoked via a smp function call, so you want
>
>      this_cpu_ptr(samples)
>
> here.

done. thanks!

>> +     /* Don't bother re-computing within 10 ms */
>> +     if (time_before(jiffies, s->jiffies + HZ/100))
>> +             goto out;
>
> That way you can spare the gotos and simply return

happy to remove the gotos, thanks!

>> index a5ce0bbe..cfc6220 100644
>> --- a/include/linux/cpufreq.h
>> +++ b/include/linux/cpufreq.h
>> @@ -883,6 +883,19 @@ static inline bool policy_has_boost_freq(struct cpufreq_policy *policy)
>>  }
>>  #endif
>>
>> +#ifdef CONFIG_X86
>> +extern unsigned int aperfmperf_khz_on_cpu(unsigned int cpu);
>> +static inline unsigned int arch_freq_get_on_cpu(int cpu)

> ... having cpu as int and unsigned int is not really consistent.

True.  the SMP code uses int cpu, while cpufreq_policy.cpu is an unsigned int.
I'll use "int cpu".

> Please don't add arch specific crap in general headers.
>
> The simple way to avoid that is to have a weak function and have an arch
> override for it. If that does not work because the cpufreq stuff must be
> built as a module, then you still can avoid CONFIG_X86 and have something
> like CONFIG_ARCH_HAS_FOO.

Thanks -- this is not modular code, and so yes, __weak works -- hadn't
had occasion to use it before...
Attached is the incremental diff responding to your comments, in case
that is convenient.
I'll re-send this series with this patch updated in a sec.

thanks,
Len Brown, Intel Open Source Technology Center
diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index 5ccf63a..d869c86 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -14,10 +14,10 @@
 #include <linux/smp.h>
 
 struct aperfmperf_sample {
-	unsigned int khz;
-	unsigned long jiffies;
-	u64 aperf;
-	u64 mperf;
+	unsigned int	khz;
+	unsigned long	jiffies;
+	u64	aperf;
+	u64	mperf;
 };
 
 static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
@@ -32,11 +32,11 @@ static void aperfmperf_snapshot_khz(void *dummy)
 {
 	u64 aperf, aperf_delta;
 	u64 mperf, mperf_delta;
-	struct aperfmperf_sample *s = &get_cpu_var(samples);
+	struct aperfmperf_sample *s = this_cpu_ptr(&samples);
 
 	/* Don't bother re-computing within 10 ms */
 	if (time_before(jiffies, s->jiffies + HZ/100))
-		goto out;
+		return;
 
 	rdmsrl(MSR_IA32_APERF, aperf);
 	rdmsrl(MSR_IA32_MPERF, mperf);
@@ -49,7 +49,7 @@ static void aperfmperf_snapshot_khz(void *dummy)
 	 * increments faster than we can read it.
 	 */
 	if (mperf_delta == 0)
-		goto out;
+		return;
 
 	/*
 	 * if (cpu_khz * aperf_delta) fits into ULLONG_MAX, then
@@ -63,12 +63,9 @@ static void aperfmperf_snapshot_khz(void *dummy)
 	s->jiffies = jiffies;
 	s->aperf = aperf;
 	s->mperf = mperf;
-
-out:
-	put_cpu_var(samples);
 }
 
-unsigned int aperfmperf_khz_on_cpu(unsigned int cpu)
+unsigned int arch_freq_get_on_cpu(int cpu)
 {
 	if (!cpu_khz)
 		return 0;
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index a667fac..6e7424d 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -632,6 +632,11 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
 show_one(scaling_min_freq, min);
 show_one(scaling_max_freq, max);
 
+__weak unsigned int arch_freq_get_on_cpu(int cpu)
+{
+	return 0;
+}
+
 static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
 {
 	ssize_t ret;
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index cfc6220..905117b 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -883,18 +883,7 @@ static inline bool policy_has_boost_freq(struct cpufreq_policy *policy)
 }
 #endif
 
-#ifdef CONFIG_X86
-extern unsigned int aperfmperf_khz_on_cpu(unsigned int cpu);
-static inline unsigned int arch_freq_get_on_cpu(int cpu)
-{
-	return aperfmperf_khz_on_cpu(cpu);
-}
-#else
-static inline unsigned int arch_freq_get_on_cpu(int cpu)
-{
-	return 0;
-}
-#endif
+extern unsigned int arch_freq_get_on_cpu(int cpu);
 
 /* the following are really really optional */
 extern struct freq_attr cpufreq_freq_attr_scaling_available_freqs;