CPU_LOAD_UPDATE(9)                        Driver Basics                        CPU_LOAD_UPDATE(9)



NAME
       cpu_load_update - update the rq->cpu_load[] statistics

SYNOPSIS
       void cpu_load_update(struct rq * this_rq, unsigned long this_load,
                            unsigned long pending_updates);

ARGUMENTS
       this_rq
           The rq to update statistics for

       this_load
           The current load

       pending_updates
           The number of missed updates

DESCRIPTION
       Update rq->cpu_load[] statistics. This function is usually called every scheduler tick
       (TICK_NSEC).

       This function computes a decaying average:

       load[i]' = (1 - 1/2^i) * load[i] + (1/2^i) * load

       Because of NOHZ it might not get called on every tick which gives need for the
       pending_updates argument.

       load[i]_n = (1 - 1/2^i) * load[i]_n-1 + (1/2^i) * load_n-1 = A * load[i]_n-1 + B ; A := (1
       - 1/2^i), B := (1/2^i) * load = A * (A * load[i]_n-2 + B) + B = A * (A * (A * load[i]_n-3
       + B) + B) + B = A^3 * load[i]_n-3 + (A^2 + A + 1) * B = A^n * load[i]_0 + (A^(n-1) +
       A^(n-2) + ... + 1) * B = A^n * load[i]_0 + ((1 - A^n) / (1 - A)) * B = (1 - 1/2^i)^n *
       (load[i]_0 - load) + load

       In the above we've assumed load_n := load, which is true for NOHZ_FULL as any change in
       load would have resulted in the tick being turned back on.

       For regular NOHZ, this reduces to:

       load[i]_n = (1 - 1/2^i)^n * load[i]_0

       see decay_load_misses. For NOHZ_FULL we get to subtract and add the extra term.

COPYRIGHT
Kernel Hackers Manual 4.8.                 January 2017                        CPU_LOAD_UPDATE(9)