Perf sched shows you scheduling latency (time spent waiting on CPU runqueue in Runnable state), but not "demand" for (some of) the system resources like the loa

Perf sched shows you scheduling latency (time spent waiting on CPU runqueue in Runnable state), but not "demand" for (some of) the system resources like the load figure tries to estimate. I think the author didn't realize that the unit of load is just "number of threads" doing _something_ (wanting to be on CPU, running on CPU or waiting for I/O in D state on Linux, just CPU stuff on other Unixes). Load average is just "average number of threads" doing something over last 1,5,15 minutes. So if just the single-number averaged over multiple minutes is not good enough for drilling down into your load spikes, then you just go look into the data source (not necessarily source code) yourself. Just use ps or /proc filesystem to list the _number of threads_ that are currently either in R or D state. That's your system load at the current moment. If you want some summary/average over 10 seconds, run the same commant 100x in a row (and sleep a bit in the between) and count all threads in R & D state (and then divide by 100 to normalize it to an average). It's basically sampling-based profiling of Linux thread states.