Re: [kvm-unit-tests PATCH] arm: Remove MAX_SMP probe loop

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On Tue, Dec 20, 2022 at 04:32:00PM +0000, Colton Lewis wrote:
> Alexandru Elisei <alexandru.elisei@xxxxxxx> writes:
> 
> > Though I'm not sure how you managed to get MAX_SMP to go down to 6 cores
> > on
> > a 12 core machine. MAX_SMP is initialized to $(getconf _NPROCESSORS_ONLN),
> > so the body of the loop should never execute. I also tried it on a 6 core
> > machine, and MAX_SMP was 6, not 3.
> 
> > Am I missing something?
> 
> To be clear, 12 cores was a simplified example I did not directly
> verify. What happened to me was 152 cores being cut down to 4. I was
> confused why one machine was running a test with 4 cores when my other
> machines were running with 8 and traced it to that loop. In effect the
> loop was doing MAX_SMP=floor(MAX_SMP / 2) until MAX_SMP <= 8. I printed
> the iterations and MAX_SMP followed the sequence 152->76->38->19->9->4.

Ah, I think I understand now. Were you running 32-bit arm tests? If so,
it'd be good to point that out explicitly in the commit message (the
'arm:' prefix in the summary is ambiguous).

Assuming the loop body was running because it needed to reduce MAX_SMP to
8 or lower for 32-bit arm tests, then we should be replacing the loop with
something that caps MAX_SMP at 8 for 32-bit arm tests instead.

Thanks,
drew



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