rpi2 head -r327485 (e.g.): rpi2 leaves one "CPU n" always idle for some boots

[Mark Millard]

I've seen this over many versions of head for months
but have never managed to find a way to force it to
happen. It just shows up once and a while.

Thus, I'm just dumping out some top and kernel information
here for reference. I've used:

openssl speed 1>/dev/null 2>&1 &
openssl speed 1>/dev/null 2>&1 &
openssl speed 1>/dev/null 2>&1 &
openssl speed 1>/dev/null 2>&1 &

to give the rpi2 4 active processes. Various outputs
are from different times without a reboot between.

top -CaePores shows the likes of:

  PID USERNAME       THR PRI NICE   SIZE    RES   SWAP STATE   C   TIME     CPU COMMAND
  614 root             1  20    0 10452K 10480K     0K select  1   0:00   0.03% /usr/sbin/ntpd -g -c /etc/ntp.conf -p /var/run/ntpd.pid -f /var/db/ntpd.drift
  661 root             1  52    0  9984K  6132K     0K select  1   0:00   0.00% /usr/sbin/sshd
  751 root             1 101    0  7256K  4276K     0K RUN     1   0:28  99.57% openssl speed
  750 root             1 100    0  7256K  4276K     0K CPU0    0   0:32  94.83% openssl speed
  753 root             1  86    0  7256K  4276K     0K RUN     3   0:13  52.36% openssl speed
  752 root             1  86    0  7256K  4276K     0K CPU3    3   0:14  46.54% openssl speed
  363 root             1  20    0  6428K  3840K     0K select  3   0:00   0.00% /sbin/devd
 . . .

and:

last pid:   754;  load averages:  3.70,  2.38,  1.58                                                                                                                            up 0+00:16:50  01:59:37
21 processes:  5 running, 16 sleeping
CPU 0: 94.9% user,  0.0% nice,  0.0% system,  5.1% interrupt,  0.0% idle
CPU 1: 99.6% user,  0.0% nice,  0.0% system,  0.4% interrupt,  0.0% idle
CPU 2:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 3:  100% user,  0.0% nice,  0.0% system,  0.0% interrupt,  0.0% idle
Mem: 12M Active, 1136K Inact, 56M Wired, 30M Buf, 722M Free
Swap: 1536M Total, 6M Free

From problem boot to problem boot, the CPU that stays
idle has varied but usually has been CPU 2. I've never
seen 2 or more stuck in idle.

show allpcpu shows the likes of:

db> show allpcpu
Current CPU: 0

cpuid        = 0
dynamic pcpu = 0x3d2540
curthread    = 0xd8478ae0: pid 2032 tid 100150 "openssl"
curpcb       = 0xd852ae98
fpcurthread  = 0xd8478ae0: pid 2032 "openssl"
idlethread   = 0xc376fae0: tid 100002 "idle: cpu0"
curpmap      = 0xd8e43bf4
curvnet      = 0

cpuid        = 1
dynamic pcpu = 0x3998540
curthread    = 0xd7e5b3a0: pid 2031 tid 100173 "openssl"
curpcb       = 0xda7e0e98
fpcurthread  = 0xd7e5b3a0: pid 2031 "openssl"
idlethread   = 0xc376f740: tid 100003 "idle: cpu1"
curpmap      = 0xd8e43ec4
curvnet      = 0

cpuid        = 2
dynamic pcpu = 0x3999540
curthread    = 0xc376f3a0: pid 10 tid 100004 "idle: cpu2"
curpcb       = 0xc378ae98
fpcurthread  = none
idlethread   = 0xc376f3a0: tid 100004 "idle: cpu2"
curpmap      = 0
curvnet      = 0

cpuid        = 3
dynamic pcpu = 0x399a540
curthread    = 0xd8477000: pid 2034 tid 100167 "openssl"
curpcb       = 0xd876de98
fpcurthread  = 0xd8477000: pid 2034 "openssl"
idlethread   = 0xc376f000: tid 100005 "idle: cpu3"
curpmap      = 0xc377ab04
curvnet      = 0

In other words: it appears that the cpuN (here cpu2) is
left with idle scheduled all the time for some reason.

ps from db> shows things like:


db> ps
  pid  ppid  pgrp   uid  state   wmesg   wchan       cmd
 2034   714  2034     0  R+                          openssl
 2033   714  2033     0  R+      CPU 3               openssl
 2032   714  2032     0  R+      CPU 0               openssl
 2031   714  2031     0  R+      CPU 1               openssl

(then later:)

db> ps
  pid  ppid  pgrp   uid  state   wmesg   wchan       cmd
 2034   714  2034     0  R+      CPU 3               openssl
 2033   714  2033     0  R+                          openssl
 2032   714  2032     0  R+      CPU 0               openssl
 2031   714  2031     0  R+      CPU 1               openssl

There is also:

   10     0     0     0  RL      (threaded)          [idle]
100002                   CanRun                      [idle: cpu0]
100003                   CanRun                      [idle: cpu1]
100004                   CanRun                      [idle: cpu2]
100005                   CanRun                      [idle: cpu3]
 

These are from:

# uname -apKU
FreeBSD rpi2 12.0-CURRENT FreeBSD 12.0-CURRENT  r327485M  arm armv7 1200054 1200054


===
Mark Millard
markmi at dsl-only.net