ports/119589: default parameter of powerd is unsuitable for multi core system.

[KOIE Hidetaka]

>Number:         119589
>Category:       ports
>Synopsis:       default parameter of powerd is unsuitable for multi core system.
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-ports-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Sat Jan 12 08:30:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     KOIE Hidetaka
>Release:        FreeBSD 8.0-CURRENT amd64
>Organization:
surigiken
>Environment:
FreeBSD guriandgura 8.0-CURRENT FreeBSD 8.0-CURRENT #0: Sat Jan 5 16:35:
45 JST 2008 koie at guriandgura:/usr/obj/usr/src/sys/GURIANDGURA amd64

>Description:
On multi core system, powerd will not increase performance.
For example, if NCPU=4 and one process consumes a CPU,
system-wide CPU idle is >= 75%.
Because the threashold is 65% by default,
powerd never increase performace.

>How-To-Repeat:

>Fix:
Change default setting:
DEFAULT_ACTIVE_PERCENT = (100 * (NCPU - 1) + 65) / NCPU,
DEFAULT_IDLE_PERCENT = (100 * (NCPU - 1) + 90) / NCPU.
if NCPU=4, 
DEFAULT_ACTIVE_PERCENT = 91,
DEFAULT_IDLE_PERCENT = 97.

Or, powerd polls per-core CPU statistics kern.cp_times
and increases performance when any CPU is busy.

Or, kernel and powerd support per-core power management.


>Release-Note:
>Audit-Trail:
>Unformatted: