Thomas Huth <thuth@xxxxxxxxxx> writes:
On 11/01/2023 22.54, 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 ==
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
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
+ 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")
+fi
Is that string with "exceeds" really still the recent error message of the
latest QEMU versions? When I'm running
qemu-system-aarch64 -machine virt -smp 1024
I'm getting:
qemu-system-aarch64: Invalid SMP CPUs 1024. The max CPUs
supported by machine 'virt-8.0' is 512
... thus no "exceeds" in here? What do I miss? Maybe it's better to just
grep for "max CPUs" ?
The full qemu command run by the test is much more complicated. It takes
a different code path and results in different errors, including the
"exceeds" one. All my testing has been done with QEMU v7.0, released
2022.
