| Message ID | 20230201172110.1970980-2-coltonlewis@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm: Replace MAX_SMP probe loop | expand |
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@google.com> > --- > 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 >
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 +# 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
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@google.com> --- scripts/runtime.bash | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-)