Patch "x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-cpu-fix-up-cpu-mhz-in-proc-cpuinfo.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Rafael J. Wysocki" <[email protected]>
Date: Fri, 3 Nov 2017 16:35:49 +0100
Subject: x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo

From: Rafael J. Wysocki <[email protected]>

commit 941f5f0f6ef5338814145cf2b813cf1f98873e2f upstream.

Commit 890da9cf0983 (Revert "x86: do not use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"") is not sufficient to restore the previous behavior of "cpu MHz" in /proc/cpuinfo on x86 due to some changes made after the commit it has reverted.

To address this, make the code in question use arch_freq_get_on_cpu() which also is used by cpufreq for reporting the current frequency of CPUs and since that function doesn't really depend on cpufreq in any way, drop the CONFIG_CPU_FREQ dependency for the object file containing it.

Also refactor arch_freq_get_on_cpu() somewhat to avoid IPIs and return cached values right away if it is called very often over a short time (to prevent user space from triggering IPI storms through it).

---
 arch/x86/kernel/cpu/Makefile     |    2 +-
 arch/x86/kernel/cpu/aperfmperf.c |   11 +++++++----
 arch/x86/kernel/cpu/proc.c       |    4 +++-
 3 files changed, 11 insertions(+), 6 deletions(-)

@@ -21,7 +21,7 @@ obj-y			+= common.o
 obj-y			+= rdrand.o
 obj-y			+= match.o
 obj-y			+= bugs.o
-obj-$(CONFIG_CPU_FREQ)	+= aperfmperf.o
+obj-y			+= aperfmperf.o
 
 obj-$(CONFIG_PROC_FS)	+= proc.o
 obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o

@@ -42,10 +42,6 @@ static void aperfmperf_snapshot_khz(void
 	s64 time_delta = ktime_ms_delta(now, s->time);
 	unsigned long flags;
 
-	/* Don't bother re-computing within the cache threshold time. */
-	if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
-		return;
-
 	local_irq_save(flags);
 	rdmsrl(MSR_IA32_APERF, aperf);
 	rdmsrl(MSR_IA32_MPERF, mperf);

@@ -74,6 +70,7 @@ static void aperfmperf_snapshot_khz(void
 
 unsigned int arch_freq_get_on_cpu(int cpu)
 {
+	s64 time_delta;
 	unsigned int khz;
 
 	if (!cpu_khz)

@@ -82,6 +79,12 @@ unsigned int arch_freq_get_on_cpu(int cp
 	if (!static_cpu_has(X86_FEATURE_APERFMPERF))
 		return 0;
 
+	/* Don't bother re-computing within the cache threshold time. */
+	time_delta = ktime_ms_delta(ktime_get(), per_cpu(samples.time, cpu));
+	khz = per_cpu(samples.khz, cpu);
+	if (khz && time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
+		return khz;
+
 	smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
 	khz = per_cpu(samples.khz, cpu);
 	if (khz)

@@ -77,9 +77,11 @@ static int show_cpuinfo(struct seq_file
 		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
 
 	if (cpu_has(c, X86_FEATURE_TSC)) {
-		unsigned int freq = cpufreq_quick_get(cpu);
+		unsigned int freq = arch_freq_get_on_cpu(cpu);
 
 		if (!freq)
+			freq = cpufreq_quick_get(cpu);
+		if (!freq)
 			freq = cpu_khz;
 		seq_printf(m, "cpu MHz\t\t: %u.%03u\n",
 			   freq / 1000, (freq % 1000));

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/revert-x86-do-not-use-cpufreq_quick_get-for-proc-cpuinfo-cpu-mhz.patch queue-4.13/pm-qos-fix-default-runtime_pm-device-resume-latency.patch queue-4.13/x86-cpu-fix-up-cpu-mhz-in-proc-cpuinfo.patch queue-4.13/pm-qos-fix-device-resume-latency-pm-qos.patch