racct: Improve handling of the pcpu resourceHEADmain

The previous scheme would inflate the CPU consumption of short-lived
processes.  For containers (e.g., processes, jails), the total pcpu
usage was computed as a sum of the pcpu usage of all constituent
threads, which makes little sense for a decaying average.

Instead, aggregate wallclock time of all on-CPU threads and compute the
pcpu resource as a decaying average as the sum.  This gives much more
reasonable and accurate values in various simple tests.

PR:		235556
Reviewed by:	markj
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D30878

0 files changed, 0 insertions, 0 deletions