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Date:   Thu,  9 Nov 2017 18:38:14 +0800
From:   WANG Chao <chao.wang@...oud.cn>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Mathias Krause <minipli@...glemail.com>, x86@...nel.org,
        stable@...nel.org
Subject: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again

Commit 941f5f0f6ef5 (x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo) caused
a serious performance issue when reading from /proc/cpuinfo on system
with aperfmperf.

For each cpu, arch_freq_get_on_cpu() sleeps 20ms to get its frequency.
On a system with 64 cpus, it takes 1.5s to finish running `cat
/proc/cpuinfo`, while it previously was done in 15ms.

Some programs use /proc/cpuinfo during startup or runtime, eg. QEMU.
This patch will restore the previous behavior and let user space happy.

Fixes: 941f5f0f6ef5 (x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo)
Cc: stable@...nel.org   # 4.13
Signed-off-by: WANG Chao <chao.wang@...oud.cn>
---
 arch/x86/kernel/cpu/Makefile | 2 +-
 arch/x86/kernel/cpu/proc.c   | 4 +---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index 236999c54edc..c60922a66385 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/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
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 4378a729b933..6b7e17bf0b71 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/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",
-- 
2.15.0


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