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> --- .../pm/intel_uncore_frequency_scaling.rst | 51 +++++++++++++++++++ 1 file changed, 51 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..fb83aa2b744e 100644 --- a/Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst +++ b/Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst @@ -113,3 +113,54 @@ 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 +------------------------------- + +In the realm of high-performance computing, particularly with Xeon +processors, managing uncore frequency is an important aspect of system +optimization. Traditionally, the uncore frequency is ramped up rapidly +in high load scenarios. While this strategy achieves low latency, which +is crucial for time-sensitive computations, it does not necessarily yield +the best performance per watt, —a key metric for energy efficiency and +operational cost savings. + +The Efficiency vs. Latency Control (ELC) feature allows user to influence +the uncore frequency scaling algorithm. Hardware monitors the average CPU +utilization across all cores at regular intervals. If the average CPU +utilization is below a user defined threshold (elc_low_threshold_percent), +the user defined uncore frequency floor frequency will be used +(elc_floor_freq_khz), minimizing latency. Similarly in high load scenario +where the CPU utilization goes above the high threshold value +(elc_high_threshold_percent) instead of jumping to maximum uncore +frequency, uncore frequency is increased in 100MHz steps until the power +limit is reached. + +Attributes for efficiency latency control: + +``elc_floor_freq_khz`` + This attribute is used to get/set the efficiency latency floor frequency. + If this variable is lower than the 'min_freq_khz', it is ignored by + the firmware. + +``elc_low_threshold_percent`` + This attribute is used to get/set the efficiency latency control low + threshold. This attribute is in percentages of CPU utilization. + +``elc_high_threshold_percent`` + This attribute is used to get/set the efficiency latency control high + threshold. This attribute is in percentages of CPU utilization. + +``elc_high_threshold_enable`` + This attribute is used to enable/disable the efficiency latency control + high threshold. Write '1' to enable, '0' to disable. + +Example system configuration below, which does following: + * when CPU utilization is less than 10%: sets uncore frequency to 800MHz + * when CPU utilization is higher than 95%: increases uncore frequency in + 100MHz steps, until power limit is reached + + elc_floor_freq_khz:800000 + elc_high_threshold_percent:95 + elc_high_threshold_enable:1 + elc_low_threshold_percent:10 -- 2.43.1
