On Wed, Feb 01, 2023 at 05:21:10PM +0000, Colton Lewis wrote:
> Replace the MAX_SMP probe loop in favor of reading a number directly
> from the QEMU error message. This is equally safe as the existing code
> because the error message has had the same format as long as it has
> existed, since QEMU v2.10. The final number before the end of the
> error message line indicates the max QEMU supports.
>
> This loop logic is broken for machines with a number of CPUs that
> isn't a power of two. This problem was noticed for gicv2 tests on
> machines with a non-power-of-two number of CPUs greater than 8 because
> tests were running with MAX_SMP less than 8. As a hypothetical example,
> a machine with 12 CPUs will test with MAX_SMP=6 because 12 >> 1 ==
> 6. This can, in rare circumstances, lead to different test results
> depending only on the number of CPUs the machine has.
>
> A previous comment explains the loop should only apply to kernels
> <=v4.3 on arm and suggests deletion when it becomes tiresome to
> maintain. However, it is always theoretically possible to test on a
> machine that has more CPUs than QEMU supports, so it makes sense to
> leave some check in place.
>
> Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx>
> ---
> scripts/runtime.bash | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/scripts/runtime.bash b/scripts/runtime.bash
> index f8794e9a..587ffe30 100644
> --- a/scripts/runtime.bash
> +++ b/scripts/runtime.bash
> @@ -188,12 +188,10 @@ function run()
> # Probe for MAX_SMP, in case it's less than the number of host cpus.
> #
> # This probing currently only works for ARM, as x86 bails on another
> -# error first. Also, this probing isn't necessary for any ARM hosts
> -# running kernels later than v4.3, i.e. those including ef748917b52
> -# "arm/arm64: KVM: Remove 'config KVM_ARM_MAX_VCPUS'". So, at some
> -# point when maintaining the while loop gets too tiresome, we can
> -# just remove it...
> -while $RUNTIME_arch_run _NO_FILE_4Uhere_ -smp $MAX_SMP \
> - |& grep -qi 'exceeds max CPUs'; do
> - MAX_SMP=$((MAX_SMP >> 1))
> -done
> +# error first. The awk program takes the last number from the QEMU
I point this awk reference out in the last review. I also stated
we should do something else, which is not done in this version.
Go read the last review comments again.
> +# error message, which gives the allowable MAX_SMP.
> +if smp=$($RUNTIME_arch_run _NO_FILE_4Uhere_ -smp $MAX_SMP \
> + |& grep 'exceeds max CPUs'); then
> + smp=${smp##*(}
> + MAX_SMP=${smp:0:-1}
> +fi
> --
> 2.39.1.456.gfc5497dd1b-goog
>
