Bug 232204 - 11.2-RELEASE on Raspberry Pi2 ignoring one CPU.
Summary: 11.2-RELEASE on Raspberry Pi2 ignoring one CPU.
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: arm (show other bugs)
Version: 11.2-RELEASE
Hardware: arm Any
: --- Affects Only Me
Assignee: freebsd-arm (Nobody)
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2018-10-12 14:33 UTC by Steve Clarke
Modified: 2018-10-12 14:53 UTC (History)
1 user (show)

See Also:


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Description Steve Clarke 2018-10-12 14:33:38 UTC
I have 2 Raspberry Pi2s running FreeBSD 11.2-RELEASE, one is using the latest image (https://download.freebsd.org/ftp/releases/ISO-IMAGES/11.2/FreeBSD-11.2-RELEASE-arm-armv6-RPI2.img.xz), the other I have built from source (r338421). Both seemed to function perfectly with no stability issues but I noticed some odd load values. Despite being 98%-100% idle, the systems show load values in the region of but never less than 1.00. After some brief investigation only CPU 0,1 and 3 are being utilised despite all 4 cores being discovered on boot. CPU 2 remains 100% idle at all times on both machines. 

root@pi2:~ # sysctl hw.ncpu
hw.ncpu: 4

Running top -P at idle shows :-

last pid:  9083;  load averages:  1.09,  1.09,  1.03    up 3+01:04:56  06:25:53
21 processes:  1 running, 20 sleeping
CPU 0:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 1:  5.3% user,  0.0% nice,  0.0% system,  0.0% interrupt, 94.7% idle
CPU 2:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 3:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
Mem: 4464K Active, 31M Inact, 72M Wired, 29M Buf, 688M Free
Swap:

Running top -P with make -j8 buildworld :-

last pid: 10475;  load averages:  8.62,  3.53,  2.06    up 3+01:16:06  14:29:56
67 processes:  12 running, 55 sleeping
CPU 0: 73.7% user,  0.0% nice, 12.5% system, 13.7% interrupt,  0.0% idle
CPU 1: 89.0% user,  0.0% nice, 11.0% system,  0.0% interrupt,  0.0% idle
CPU 2:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 3: 82.0% user,  0.0% nice,  6.7% system, 11.4% interrupt,  0.0% idle
Mem: 113M Active, 92M Inact, 93M Wired, 38M Buf, 498M Free
Swap:
Comment 1 Mark Millard 2018-10-12 14:53:24 UTC
(In reply to Steve Clarke from comment #0)

I do not not normally use RPI2's any more but I
will note that historically I've seen this "only
uses 3 of 4 cpus" multiple times in the past,
going back well before 11.2 .

Mostly this note is just letting you know that
it is not only you, at least from a history going
back before 11.2 .

I never managed to isolate anything about controlling
when it happened or just what was happening internally
when it did happen.