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.

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