On Tue, Feb 07, 2023 at 11:32:56PM +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 | 17 ++++++++--------- > 1 file changed, 8 insertions(+), 9 deletions(-) > > v5: Remove the last awk reference and guard the probing code with a > check that ARCH = arm or arm64. > > v4: https://lore.kernel.org/kvm/20230201172110.1970980-1-coltonlewis@xxxxxxxxxx/ > > v3: https://lore.kernel.org/kvm/20230130195700.729498-1-coltonlewis@xxxxxxxxxx/ > > v2: https://lore.kernel.org/kvm/20230111215422.2153645-1-coltonlewis@xxxxxxxxxx/ > > v1: https://lore.kernel.org/kvm/20221219185250.631503-1-coltonlewis@xxxxxxxxxx/ > > diff --git a/scripts/runtime.bash b/scripts/runtime.bash > index f8794e9a..fb64e855 100644 > --- a/scripts/runtime.bash > +++ b/scripts/runtime.bash > @@ -188,12 +188,11 @@ 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, so this check is only run for ARM and ARM64. The > +# parameter expansion takes the last number from the QEMU error > +# message, which gives the allowable MAX_SMP. > +if [ "${ARCH%64}" = arm ] && smp=$($RUNTIME_arch_run _NO_FILE_4Uhere_ -smp $MAX_SMP \ I'd rather be more explicit. I'll change this to if [[ $ARCH == 'arm' || $ARCH == 'arm64' ]] && smp=... and merge it. Thanks, drew > + |& grep 'exceeds max CPUs'); then > + smp=${smp##*(} > + MAX_SMP=${smp:0:-1} > +fi > -- > 2.39.1.519.gcb327c4b5f-goog
