On Wed, Jan 11, 2023 at 09:54:22PM +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. A short awk
> program is used to extract the number, which becomes the new MAX_SMP
> value.
>
> This loop logic is broken for machines with a number of CPUs that
> isn't a power of two. A machine with 8 CPUs will test with MAX_SMP=8
> but a machine with 12 CPUs will test with MAX_SMP=6 because 12 >> 2 ==
^ 1
> 6. This can, in rare circumstances, lead to different test results
> depending only on the number of CPUs the machine has.
I guess that problem doesn't go away if we don't set the number of CPUs
to be the same, regardless of machine, i.e. we're still picking a
machine-specific value when we pick MAX_SMP. I think I know what you
mean though. For gicv2 tests on machines that support non-power-of-2
CPUs greater than 8 it's possible to end up with less than 8 for
MAX_SMP, which is surprising. Maybe while fixing the shift above you
can change the text to be more in line with that?
>
> A previous comment explains the loop should only apply to kernels
> <=v4.3 on arm and suggests deletion when it becomes tiresome to
> maintian. 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 f8794e9..4377e75 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
> +# error message, which gives the allowable MAX_SMP.
> +if $RUNTIME_arch_run _NO_FILE_4Uhere_ -smp $MAX_SMP \
> + |& grep -qi 'exceeds max CPUs'; then
If the message has always been the same then the -i on grep shouldn't be
necessary.
> + GET_LAST_NUM='/exceeds max CPUs/ {match($0, /[[:digit:]]+)$/); print substr($0, RSTART, RLENGTH-1)}'
> + MAX_SMP=$($RUNTIME_arch_run _NO_FILE_4Uhere_ -smp $MAX_SMP |& awk "$GET_LAST_NUM")
We should restructure this so we only have to invoke QEMU once and I
think we can do it with just bash and grep. Something like
if smp=$($RUNTIME_arch_run _NO_FILE_4Uhere_ -smp $MAX_SMP |& grep 'exceeds max CPUs'); then
smp=${smp##*\(}
MAX_SMP=${smp:0:-1}
fi
Thanks,
drew
