Re: [PATCH] smp: Add bootcpus parameter to boot subset of CPUs

[Thomas Gleixner]

On Fri, Oct 30 2020 at 17:45, Sudeep Holla wrote:
> On Thu, Oct 29, 2020 at 02:37:06PM -0700, Elliot Berman wrote:
>> In the case where commercial device is using feature for thermal, device
>> should boot multiple small cores. Booting only one core means we would not
>> be able to use all possible cores to maximum extent possible in this thermal
>> case.
>
> I understood that point. But you haven't responded on my logical vs physical
> number argument. I am clearly NACKing this patch as is for just usage of
> logical CPU IDs in the command line while your intention is to control
> the physical CPUs. So once again, NACK for that reason.

Correct. And no, we are not going to add a command line option to select
physical CPU ids.

There are two ways to solve that:

  1) The firmware can tell the kernel whether a CPU should be brought up
     or not, e.g. by failing the bootup request.

  2) The kernel has a way to figure out the current thermal and/or power
     budget early in the boot process and sorts out which and how many
     CPUs fit into that limit.

Thanks,

        tglx