On Thu, 2024-08-29 at 12:18 +0300, Ilpo Järvinen wrote: > On Wed, 28 Aug 2024, Tero Kristo wrote: > > > Added documentation about the functionality of efficiency vs. > > latency tradeoff > > control in intel Xeon processors, and how this is configured via > > sysfs. > > > > Signed-off-by: Tero Kristo <tero.kristo@xxxxxxxxxxxxxxx> > > --- > > v2: > > * Largely re-wrote the documentation > > > > .../pm/intel_uncore_frequency_scaling.rst | 59 > > +++++++++++++++++++ > > 1 file changed, 59 insertions(+) > > > > diff --git a/Documentation/admin- > > guide/pm/intel_uncore_frequency_scaling.rst b/Documentation/admin- > > guide/pm/intel_uncore_frequency_scaling.rst > > index 5ab3440e6cee..26ded32b06f5 100644 > > --- a/Documentation/admin- > > guide/pm/intel_uncore_frequency_scaling.rst > > +++ b/Documentation/admin- > > guide/pm/intel_uncore_frequency_scaling.rst > > @@ -113,3 +113,62 @@ to apply at each uncore* level. > > > > Support for "current_freq_khz" is available only at each fabric > > cluster > > level (i.e., in uncore* directory). > > + > > +Efficiency vs. Latency Tradeoff > > +------------------------------- > > + > > +The Efficiency Latency Control (ELC) feature improves performance > > +per watt. With this feature hardware power management algorithms > > +optimize trade-off between latency and power consumption. For some > > +latency sensitive workloads further tuning can be done by SW to > > +get desired performance. > > + > > +The hardware monitors the average CPU utilization across all cores > > +in a power domain at regular intervals and decides an uncore > > frequency. > > +While this may result in the best performance per watt, workload > > may be > > +expecting higher performance at the expense of power. Consider an > > +application that intermittently wakes up to perform memory reads > > on an > > +otherwise idle system. In such cases, if hardware lowers uncore > > +frequency, then there may be delay in ramp up of frequency to meet > > +target performance. > > + > > +The ELC control defines some parameters which can be changed from > > SW. > > +If the average CPU utilization is below a user defined threshold > > +(elc_low_threshold_percent attribute below), the user defined > > uncore > > +frequency floor frequency will be used (elc_floor_freq_khz > > attribute > > Consider the following simplification: > > "the user defined uncore frequency floor frequency" -> > "the user-defined uncore floor frequency" > > I think it tells the same even without that first "frequency". > > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> > Yeah, it looks kind of silly. I think that's just a typo from my side, thanks for catching. -Tero
