Commits on Jul 18, 2024

1. scx_bpfland: introduce dynamic nvcsw threshold …

   Instead of using a static value to classify tasks based on their average
   amount of voluntary context switches, try to periodically evaluate an
   optimal threshold, based on a global average of voluntary context
   switches among of all the running tasks.
   
   Tasks with an average amount of voluntary context switches greater than
   the global average will be classified as interactive.
   
   The global average is evaluated as an exponentially weighted moving
   average (EWMA), as:
   
     avg(t) = avg(t - 1) * 0.75 - task_avg(t) * 0.25
   
   This approach is more efficient than iterating through all tasks and it
   helps to prevent rapid fluctuations that may be caused by bursts of
   voluntary context switch events.
   
   The dynamic nvcsw threshold enables a more precise adjustment of
   the classification criteria to swiftly respond to global system changes:
   tasks can be quickly classified as interactive, but if the system
   experiences too many interactive events, the criteria for maintaining
   interactive status become stricter. This creates a natural selection
   process where only the most deserving tasks remain interactive.
   
   Additionally, introduce the new option `--nvcsw-max-thresh N`, which
   allows to extend or restrict the fluctuation range of the global average
   threshold for voluntary context switches.
   
   Tested-by: Piotr Gorski <[email protected]>
   Signed-off-by: Andrea Righi <[email protected]>

   

   arighi committed Jul 18, 2024
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