On Tue, Mar 15, 2022 at 04:31:34PM +0000, Alexandru Elisei wrote:
> Well, kvm-unit-tests selects KVM or TCG under the hood without the user
> being involved at all.
The under the hood aspect isn't great. It's best for testers to know what
they're testing. It's pretty obvious, though, that if you choose
ARCH != HOST that you'll end up on TCG. And, since KVM has historically
been the primary focus of kvm-unit-tests, then it's probably reasonable
to assume KVM is used when ARCH == HOST. However, we still silently fall
back to TCG, even when ARCH == HOST, if /dev/kvm isn't available! And,
the whole AArch32 guest support on AArch64 hosts with KVM requiring a
different qemu binary muddies things further...
Anyway, I hope serious test runners always specify ACCEL and QEMU to
whatever they plan to test.
> In my opinion, it's slightly better from an
> usability perspective for kvm-unit-tests to do its best to run the tests
> based on what the user specifically set (QEMU=qemu-system-arm) than fail to
> run the tests because of an internal heuristic of which the user might be
> entirely ignorant (if arm64 and /dev/kvm is available, pick ACCEL=kvm).
If you'd like to post a patch for it, then I'd prefer something like
below, which spells out the condition that the override is applied
and also allows $QEMU to be checked by search_qemu_binary() before
using it to make decisions.
Thanks,
drew
diff --git a/arm/run b/arm/run
index 28a0b4ad2729..128489125dcb 100755
--- a/arm/run
+++ b/arm/run
@@ -10,16 +10,24 @@ if [ -z "$KUT_STANDALONE" ]; then
fi
processor="$PROCESSOR"
-ACCEL=$(get_qemu_accelerator) ||
+accel=$(get_qemu_accelerator) ||
exit $?
-if [ "$ACCEL" = "kvm" ]; then
+if [ "$accel" = "kvm" ]; then
QEMU_ARCH=$HOST
fi
qemu=$(search_qemu_binary) ||
exit $?
+if [ "$QEMU" ] && [ -z "$ACCEL" ] &&
+ [ "$HOST" = "aarch64" ] && [ "$ARCH" = "arm" ] &&
+ [ "$(basename $QEMU)" = "qemu-system-arm" ]; then
+ accel=tcg
+fi
+
+ACCEL=$accel
+
if ! $qemu -machine '?' 2>&1 | grep 'ARM Virtual Machine' > /dev/null; then
echo "$qemu doesn't support mach-virt ('-machine virt'). Exiting."
exit 2
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