• Valentin Schneider's avatar
    arch_topology, arm, arm64: define arch_scale_freq_invariant() · 15e5d5b4
    Valentin Schneider authored
    arch_scale_freq_invariant() is used by schedutil to determine whether
    the scheduler's load-tracking signals are frequency invariant. Its
    definition is overridable, though by default it is hardcoded to 'true'
    if arch_scale_freq_capacity() is defined ('false' otherwise).
    
    This behaviour is not overridden on arm, arm64 and other users of the
    generic arch topology driver, which is somewhat precarious:
    arch_scale_freq_capacity() will always be defined, yet not all cpufreq
    drivers are guaranteed to drive the frequency invariance scale factor
    setting. In other words, the load-tracking signals may very well *not*
    be frequency invariant.
    
    Now that cpufreq can be queried on whether the current driver is driving
    the Frequency Invariance (FI) scale setting, the current situation can
    be improved. This combines the query of whether cpufreq supports the
    setting of the frequency scale factor, with whether all online CPUs are
    counter-based FI enabled.
    
    While cpufreq FI enablement applies at system level, for all CPUs,
    counter-based FI support could also be used for only a subset of CPUs to
    set the invariance scale factor. Therefore, if cpufreq-based FI support
    is present, we consider the system to be invariant. If missing, we
    require all online CPUs to be counter-based FI enabled in order for the
    full system to be considered invariant.
    
    If the system ends up not being invariant, a new condition is needed in
    the counter initialization code that disables all scale factor setting
    based on counters.
    
    Precedence of counters over cpufreq use is not important here. The
    invariant status is only given to the system if all CPUs have at least
    one method of setting the frequency scale factor.
    Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
    Signed-off-by: default avatarIonela Voinescu <ionela.voinescu@arm.com>
    Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    Acked-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
    Reviewed-by: default avatarSudeep Holla <sudeep.holla@arm.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    15e5d5b4
topology.h 985 Bytes