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

[Allan Jude]

On 2018-01-02 14:48, Mark Millard wrote:
> 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
> 
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> 

Have you tried using 'cpuset' to force each of the 4 to run on a
specific CPU? What happens if you force it to run on cpu #2?

-- 
Allan Jude