Re: sched: Question about big and little cores system with SMP and EAS

[Peter Zijlstra]

On Wed, Jun 16, 2021 at 07:29:26PM +0800, Ley Foon Tan wrote:
> Hi all
> 
> Would like to ask the experts here regarding the Symmetric
> Multi-Processing mode (SMP) with Energy aware scheduler (EAS) support
> on the big + little cores system.

And the you ask a question unrelated to either Symmetric MP or EAS :-)

> Hardware system:
> Big and little cores have almost the same ISA, but the big core has
> some extension instructions that little core doesn't have.

That problem is unrelated to big.Little / EAS, also by definition that
is not SMP seeing how the 'S' is a blatant lie.

The simplest solution is to simply disallow usage of the extended ISA
and force mandate the common subset. The complicated answer is something
along the lines of:

  https://lkml.kernel.org/r/20210608180313.11502-1-will@xxxxxxxxxx