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

This reverts commit 941f5f0f6e.

Sadly, it turns out that we really can't just do the cross-CPU IPI to
all CPU's to get their proper frequencies, because it's much too
expensive on systems with lots of cores.

So we'll have to revert this for now, and revisit it using a smarter
model (probably doing one system-wide IPI at open time, and doing all
the frequency calculations in parallel).

Reported-by: WANG Chao <chao.wang@ucloud.cn>
Reported-by: Ingo Molnar <mingo@kernel.org>
Cc: Rafael J Wysocki <rafael.j.wysocki@intel.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/cpu/Makefile

@@ -22,7 +22,7 @@ obj-y			+= common.o
 obj-y			+= rdrand.o
 obj-y			+= match.o
 obj-y			+= bugs.o
-obj-y			+= aperfmperf.o
+obj-$(CONFIG_CPU_FREQ)	+= aperfmperf.o
 
 obj-$(CONFIG_PROC_FS)	+= proc.o
 obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o

arch/x86/kernel/cpu/aperfmperf.c

@@ -42,6 +42,10 @@ static void aperfmperf_snapshot_khz(void *dummy)
 	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);
@@ -70,7 +74,6 @@ static void aperfmperf_snapshot_khz(void *dummy)
 
 unsigned int arch_freq_get_on_cpu(int cpu)
 {
-	s64 time_delta;
 	unsigned int khz;
 
 	if (!cpu_khz)
@@ -79,12 +82,6 @@ unsigned int arch_freq_get_on_cpu(int cpu)
 	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)

arch/x86/kernel/cpu/proc.c

@@ -78,10 +78,8 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
 
 	if (cpu_has(c, X86_FEATURE_TSC)) {
-		unsigned int freq = arch_freq_get_on_cpu(cpu);
+		unsigned int freq = cpufreq_quick_get(cpu);
 
-		if (!freq)
-			freq = cpufreq_quick_get(cpu);
 		if (!freq)
 			freq = cpu_khz;
 		seq_printf(m, "cpu MHz\t\t: %u.%03u\n",