1. How to see the number of active CPU
root@st:~# cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 0 (v7l)
BogoMIPS : 2387.14
Features : swp half thumb fastmult vfp edsp neon vfpv3 tls
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x3
CPU part : 0xc09
CPU revision : 0
processor : 1
model name : ARMv7 Processor rev 0 (v7l)
BogoMIPS : 2393.70
Features : swp half thumb fastmult vfp edsp neon vfpv3 tls
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x3
CPU part : 0xc09
CPU revision : 0
Hardware : STi SoC with Flattened Device Tree
Revision : 0000
Serial : 0000000000000000
2. How to disable a CPU
On this example we disable CPU1
root@st:~# echo 0 > /sys/devices/system/cpu/cpu1/online
CPU1: shutdown
root@st:~# cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 0 (v7l)
BogoMIPS : 2387.14
Features : swp half thumb fastmult vfp edsp neon vfpv3 tls
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x3
CPU part : 0xc09
CPU revision : 0
Hardware : STi SoC with Flattened Device Tree
Revision : 0000
Serial : 0000000000000000
3. How to enable a disabled CPU
On this example we enable CPU1
root@st:~# echo 1 > /sys/devices/system/cpu/cpu1/online
CPU1: shutdown