• Rafael J. Wysocki's avatar
    cpufreq: schedutil: New governor based on scheduler utilization data · 9bdcb44e
    Rafael J. Wysocki authored
    Add a new cpufreq scaling governor, called "schedutil", that uses
    scheduler-provided CPU utilization information as input for making
    its decisions.
    Doing that is possible after commit 34e2c555 (cpufreq: Add
    mechanism for registering utilization update callbacks) that
    introduced cpufreq_update_util() called by the scheduler on
    utilization changes (from CFS) and RT/DL task status updates.
    In particular, CPU frequency scaling decisions may be based on
    the the utilization data passed to cpufreq_update_util() by CFS.
    The new governor is relatively simple.
    The frequency selection formula used by it depends on whether or not
    the utilization is frequency-invariant.  In the frequency-invariant
    case the new CPU frequency is given by
    	next_freq = 1.25 * max_freq * util / max
    where util and max are the last two arguments of cpufreq_update_util().
    In turn, if util is not frequency-invariant, the maximum frequency in
    the above formula is replaced with the current frequency of the CPU:
    	next_freq = 1.25 * curr_freq * util / max
    The coefficient 1.25 corresponds to the frequency tipping point at
    (util / max) = 0.8.
    All of the computations are carried out in the utilization update
    handlers provided by the new governor.  One of those handlers is
    used for cpufreq policies shared between multiple CPUs and the other
    one is for policies with one CPU only (and therefore it doesn't need
    to use any extra synchronization means).
    The governor supports fast frequency switching if that is supported
    by the cpufreq driver in use and possible for the given policy.
    In the fast switching case, all operations of the governor take
    place in its utilization update handlers.  If fast switching cannot
    be used, the frequency switch operations are carried out with the
    help of a work item which only calls __cpufreq_driver_target()
    (under a mutex) to trigger a frequency update (to a value already
    computed beforehand in one of the utilization update handlers).
    Currently, the governor treats all of the RT and DL tasks as
    "unknown utilization" and sets the frequency to the allowed
    maximum when updated from the RT or DL sched classes.  That
    heavy-handed approach should be replaced with something more
    subtle and specifically targeted at RT and DL tasks.
    The governor shares some tunables management code with the
    "ondemand" and "conservative" governors and uses some common
    definitions from cpufreq_governor.h, but apart from that it
    is stand-alone.
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Acked-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Makefile 1.18 KB