• Rafael J. Wysocki's avatar
    x86 / CPU: Always show current CPU frequency in /proc/cpuinfo · 7d5905dc
    Rafael J. Wysocki authored
    After commit 890da9cf (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: 890da9cf (Revert "x86: do not use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"")
    Signed-off-by: 's avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Acked-by: 's avatarThomas Gleixner <tglx@linutronix.de>
    Tested-by: 's avatarThomas Gleixner <tglx@linutronix.de>
    Acked-by: 's avatarIngo Molnar <mingo@kernel.org>