Messages in this thread | | | Subject | Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again | From | "Rafael J. Wysocki" <> | Date | Thu, 9 Nov 2017 17:06:41 +0100 |
| |
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@kernel.org # 4.13 > Signed-off-by: WANG Chao <chao.wang@ucloud.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",
| |