Sorry I missed this email earlier.
Andrew Jones <andrew.jones@xxxxxxxxx> writes:
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?
I will rephrase the message and fix the shift.
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.
True. I was only copying the grep command that was there.
+ 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
Good idea.
