The perf sched latency tool can calculate the latency of a thread being scheduled by the operating system, which is the time between wakeup and schedule-in of task.
/*
* Explanation of delta-time stats:
*
* t = time of current schedule out event
* tprev = time of previous sched out event
* also time of schedule-in event for current task
* last_time = time of last sched change event for current task
* (i.e, time process was last scheduled out)
* ready_to_run = time of wakeup for current task
*
* -----|------------|------------|------------|------
* last ready tprev t
* time to run
*
* |-------- dt_wait --------|
* |- dt_delay -|-- dt_run --|
*
* dt_run = run time of current task
* dt_wait = time between last schedule out event for task and tprev
* represents time spent off the cpu
* dt_delay = time between wakeup and schedule-in of task
*/
time cpu task name wait time sch delay run time
[tid/pid] (msec) (msec) (msec)
--------------- ------ ------------------------------ --------- --------- ---------
43721.001384 [0001] <idle> 0.000 0.000 0.000
43721.001401 [0001] avahi-daemon[950] 0.000 0.000 0.017
43721.001451 [0000] <idle> 0.000 0.000 0.000
43721.001468 [0000] Chrome_IOThread[2401/2383] 0.000 0.000 0.016
43721.001516 [0004] <idle> 0.000 0.000 0.000
What factors can affect this latency? Will factors such as "CPU migration" or "the number of threads" or "CPU performance per core" have an impact? Will cgroups increase the latency?
I found that the latency of the same process in AMD 9654+kernel 5.14 environment is larger than that in Intel 8352Y+kernel 4.18 environment.