i.MX6D dynamic CPU status changing by CONFIG_HOTPLUG_CPU.

[satoshishimoda]

Hi community,

Our partner met a kernel panic with jb4.2.2_1.1.0-ga on a i.MX6D based custom board.

They found the kernel panic was occurred by CPU status changing (idle <--> online) on unexpected timing.

So our partner think this problem will be prevented if they stop dynamic CPU status changing.

Then, they understand the dynamic CPU status changing is enabled by the following config, so they consider disable this config.

CONFIG_HOTPLUG_CPU

[Question]

Would you let me know whether the dynamic CPU status changing is able to be prevented by disabling CONFIG_HOTPLUG_CPU?

If it can, would you let me know the side effect and concern by disabling CONFIG_HOTPLUG_CPU?

Best Regards,

Satoshi Shimoda

[AnsonHuang · Accepted solution]

Hi, Satoshi

     The CONFIG_HOTPLUG_CPU should only impact the cpu hotplug feature, which means: when kernel boot up with two cores by default on i.MX6D, you can dynamically power down secondary core by "echo 0 > /sys/devices/system/cpu/cpu1/online", and power up the secondary back by echo 1 to same interface. when you mean the CPU status change, can you describe it more detailful? As far as I know, when CPU in idle, we do NOT power down CPU1 at all on i.MX6D, which means the cpu hotplug never happen during cpu status of idle<->run change, unless there is something special done by customer, can you help check when cpu is in idle, "cat /sys/devices/system/cpu/cpu1/online" to see if it is 1, 1 means CPU1 is still online, 0 means it is power off.

     If you disable the CONFIG_HOTPLUG_CPU, then cpu hotplug will be disabled, standby mode power number will be higher, and all features depends on cpu hotplug will miss. I do NOT think cpu hotplug is the root cause.