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Date: Thu, 9 Nov 2017 17:06:41 +0100 From: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com> To: WANG Chao <chao.wang@...oud.cn>, Linus Torvalds <torvalds@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Vikas Shivappa <vikas.shivappa@...ux.intel.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, "Rafael J. Wysocki" <rafael@...nel.org>, Linux PM <linux-pm@...r.kernel.org> Subject: Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again Hi Linus, On 11/9/2017 11:38 AM, WANG Chao wrote: > 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. Honestly, I'm not sure what to do to address this ATM. The last requested frequency is only available in the non-HWP case, so it cannot be used universally. > 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",
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