Help understanding a PM (Performance Monitoring) log data

Jakub · January 7, 2019, 9:28am

Hi,

As the wiki page for this topic seems to be slightly outdated (a github’s issue is already pending… https://github.com/ArduPilot/ardupilot_wiki/issues/1061), here’s what I’d like to understand better:

MaxT - what is the limit for a scheduler’s loop? The wiki mentions 10ms, however I noticed that the NLon field lists a number whenever MaxT exceeds 3ms. Then, knowing that we did NLoops of 4000 in 10s (400Hz frequency), it seems like the limit should be at 2,5ms!
Mem - what exactly is it, RAM usage in bytes?
Load - again, what exactly does it show (units?)? What are the acceptable values?

On a sidenote, I’m running ArduCopter software (but the issue seems general enough not to assign it to a specific category).

peterbarker · January 7, 2019, 10:27am

MaxT - what is the limit for a scheduler¢s loop? The wiki mentions 10ms, however I noticed that the NLon field lists a number whenever MaxT exceeds
3ms. Then, knowing that we did NLoops of 4000 in 10s (400Hz frequency), it seems like the limit should be at 2,5ms!

The scheduler loop rate is found in SCHED_LOOP_RATE - the default differs
based on vehicle type, and any fixed number is going to be wrong

We allow a 20% leeway on long-running loops
(ardupilot/libraries/AP_Scheduler/PerfInfo.cpp at master · ArduPilot/ardupilot · GitHub)

Mem - what exactly is it, RAM usage in bytes?

Available memory, in bytes.

Load - again, what exactly does it show (units?)? What are the acceptable values?

Basically a percentage times 10. The derivations of the number is
complicated FWIR; basically based on free time remaining in the loop

github.com

ardupilot/ardupilot/blob/master/libraries/AP_Scheduler/AP_Scheduler.cpp#L223


      
          }
          
          const AP_Scheduler::Task &task = run_vehicle_task ? _vehicle_tasks[vehicle_tasks_offset] : _common_tasks[common_tasks_offset];
          if (run_vehicle_task) {
              vehicle_tasks_offset++;
          } else {
              common_tasks_offset++;
          }
          
          if (task.priority > MAX_FAST_TASK_PRIORITIES) {
              const uint16_t dt = _tick_counter - _last_run[i];
              // we allow 0 to mean loop rate
              uint32_t interval_ticks = (is_zero(task.rate_hz) ? 1 : _loop_rate_hz / task.rate_hz);
              if (interval_ticks < 1) {
                  interval_ticks = 1;
              }
              if (dt < interval_ticks) {
                  // this task is not yet scheduled to run again
                  continue;
              }
              // this task is due to run. Do we have enough time to run it?

Peter

Jakub · January 11, 2019, 10:37am

Thank’s a lot! I’ve corrected the wiki page with outdated data, here’s a PR: https://github.com/ArduPilot/ardupilot_wiki/pull/1570