https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=206961
Bug ID: 206961
Summary: powerd broken on SMP
Product: Base System
Version: 10.2-RELEASE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Some People
Priority: ---
Component: bin
Assignee: freebsd-b...@freebsd.org
Reporter: dur...@octopus.com.au
CC: freebsd-amd64@FreeBSD.org
CC: freebsd-amd64@FreeBSD.org
bug 125141 is marked FIXED, but I see it.
background:
2-way Xeon E5-2690 system
/etc/rc.conf:
powerd_enable="YES"
performance_cx_lowest="Cmax"
economy_cx_lowest="Cmax"
Consider these three cases:
1) Load no CPUs
powerd works here. All cores run at reduced frequencies and enter deep sleep
states.
2) Load all CPUs
powerd works here. All cores run at high frequency and spend essentially all
time in C0. (Actually, after a couple of minutes the system (hardware) alarm
goes off because the CPUs are overheating; FreeBSD ignores that I guess, but
let's worry about that some other day...)
3) Load one CPU
Expected:
One CPU runs at maximum ("boost") frequency and spends ~100% time in C0.
(hardware-specific technicality: the core's "pair" spends 100% time in C1.)
Other cores run at minimum frequency in deep(er) sleep.
Observed:
All CPUs stay in sleep states, though all of them average frequencies >30%
above minimum. One core will average around 2% in C0 and will run at a higher
(though not maximum) frequency.
It looks like there is some serious brokenness in SMP. #125141 makes it seem
like powerd can be expected to do the right thing, but I seem to get the worst
of both worlds: increased power consumption as all cores stay out of deep sleep
and run at elevated frequencies, and decreased performance as no one core stays
in C0 running and peak frequency.
Perhaps interestingly, this problem can be exacerbated by setting
dev.cpu.<pick_one>.cx_lowest=C1 . (Which is necessary on my system to avoid USB
keyboard stuttering, but that's another issue...) It's not clear to me, then,
that this is "the same" as #125141. Maybe it is, or maybe there remains
something fundamentally wrong with powerd in (variable frequency, variable
sleep) SMP scenarios.
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
freebsd-amd64@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/freebsd-amd64
To unsubscribe, send any mail to "freebsd-amd64-unsubscr...@freebsd.org"
