https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246940
Bug ID: 246940
Summary: [wishlist/enhancement, patch incl.]: idle user tasks
should be charged as "nice" or "user" CPU time
Product: Base System
Version: Unspecified
Hardware: Any
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: torsten.eichsta...@web.de
Created attachment 215172
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=215172&action=edit
Patch for FreeBSD-12: sys.kern.kern_clock.c.diff
Currently idle user tasks are charged as "user" CPU time.
1. This is counter-intuitive. Instead, one would expect the requested
behaviour.
2. The chargement of user tasks affects the decisions taken by a CPU freq
manager (i.e. powerd(8), sysutils/powerdxx(8) and the according kernel modules)
and thus can result in great power savings for mobile users, and/or a less
noisier system for desktop users, provided the user does not care about the
runtime of background tasks, since power managers do not increase CPU freq on
behalve of idle user tasks.
3. The patch might affect the CPU scheduler, please check. I have no clue
about this.
4. The patch introduces a new global integer sysctl "kern.cp_time_mode":
[value: behaviour; use-case]
1: charge idle threads as "nice" CPU time; suggested as server mode
2: " "idle" CPU time; suggested as mobile/desktop mode
0/any other: " "user" CPU time; (default); current behaviour
I would be interested in how such "static" sysctl's are handled on a SMP
system. If "OID_AUTO" results in a per-CPU var, a system could be partitioned
to have "interesting" behaviour :)
Onother question I have is if kernel tasks (other than the idle task itself)
could ever be in the idle class.
I ran this trivial patch on two laptops for several years w/o problems.
There might be implicit assumptions on the CPU scheduling class beeing "user"
or "nice" in some base system tasks or scripts, though.
Suggested application is to switch between "server" and "mobile" mode from
/etc/power_profile (I'm willing to patch that, it's trivial) and to allow
security.bsd.unprivileged_idprio=1. Then a desktop/mobile user can choose to
run cron(8), sysutils/anacron(8) and his own user background tasks as "idle",
and enjoy increased battery runtime and a quiter system.
How can I add more than one attachment? The patch for FreeBSD 10/11 is
slightly different, statclock() was named statclock_cnt() and did not have a
comment.
With kind regards, Torsten
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