sched/pelt: Fix task util_est update filtering

Being called for each dequeue, util_est reduces the number of its updates
by filtering out when the EWMA signal is different from the task util_avg
by less than 1%. It is a problem for a sudden util_avg ramp-up. Due to the
decay from a previous high util_avg, EWMA might now be close enough to
the new util_avg. No update would then happen while it would leave
ue.enqueued with an out-of-date value.

Taking into consideration the two util_est members, EWMA and enqueued for
the filtering, ensures, for both, an up-to-date value.

This is for now an issue only for the trace probe that might return the
stale value. Functional-wise, it isn't a problem, as the value is always
accessed through max(enqueued, ewma).

This problem has been observed using LISA's UtilConvergence:test_means on
the sd845c board.

No regression observed with Hackbench on sd845c and Perf-bench sched pipe
on hikey/hikey960.

Signed-off-by: Vincent Donnefort <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Dietmar Eggemann <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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