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After commit890da9cf09(Revert "x86: do not use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"") the "cpu MHz" number in /proc/cpuinfo on x86 can be either the nominal CPU frequency (which is constant) or the frequency most recently requested by a scaling governor in cpufreq, depending on the cpufreq configuration. That is somewhat inconsistent and is different from what it was before 4.13, so in order to restore the previous behavior, make it report the current CPU frequency like the scaling_cur_freq sysfs file in cpufreq. To that end, modify the /proc/cpuinfo implementation on x86 to use aperfmperf_snapshot_khz() to snapshot the APERF and MPERF feedback registers, if available, and use their values to compute the CPU frequency to be reported as "cpu MHz". However, do that carefully enough to avoid accumulating delays that lead to unacceptable access times for /proc/cpuinfo on systems with many CPUs. Run aperfmperf_snapshot_khz() once on all CPUs asynchronously at the /proc/cpuinfo open time, add a single delay upfront (if necessary) at that point and simply compute the current frequency while running show_cpuinfo() for each individual CPU. Also, to avoid slowing down /proc/cpuinfo accesses too much, reduce the default delay between consecutive APERF and MPERF reads to 10 ms, which should be sufficient to get large enough numbers for the frequency computation in all cases. Fixes:890da9cf09(Revert "x86: do not use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"") Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Ingo Molnar <mingo@kernel.org>
32 lines
698 B
C
32 lines
698 B
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/cpufreq.h>
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/proc_fs.h>
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#include <linux/seq_file.h>
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__weak void arch_freq_prepare_all(void)
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{
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}
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extern const struct seq_operations cpuinfo_op;
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static int cpuinfo_open(struct inode *inode, struct file *file)
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{
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arch_freq_prepare_all();
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return seq_open(file, &cpuinfo_op);
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}
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static const struct file_operations proc_cpuinfo_operations = {
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.open = cpuinfo_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = seq_release,
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};
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static int __init proc_cpuinfo_init(void)
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{
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proc_create("cpuinfo", 0, NULL, &proc_cpuinfo_operations);
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return 0;
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}
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fs_initcall(proc_cpuinfo_init);
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