halting the kernel does not stop the CPU cores?

[Florian Fainelli]

On 07/27/2017 07:38 AM, Heinz Wrobel wrote:
> Hi,
> 
> I noticed that when halting the kernel (intentionally or not), the cores effectively go into a while(1) loop and power consumption on larger devices really jumps up significantly to the point where, e.g., a “crash” turns into “crash and burn”.
> 
> I would assume that if a system is halted, you don’t want to dissipate more power than on a running system but go as silent as low power as reasonable.
> 
> Is there any specific reason why the cores would not go into a wfi loop like they do on idle?
> The patch to fix this seems to be easy at first glance, but is there a good reason *NOT* to do such a patch and to leave the plain while(1)?

In fact, if your platform supports CPU_HOTPLUG, I am not clear why
smp_send_stop() + ipi_send_stop() is not calling platform_cpu_kill()
which would be smp_ops.cpu_kill() but instead cpu_relax() was chosen?

The CPU is dead anyway so as you say, so it's not like there is a remote
chance to resume execution on these secondary cores?
--
Florian