[PATCH tip/core/rcu 13/21] rcutorture: Tweak kvm options

[Paul E. McKenney]

From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

In one of my rcutorture tests the TSC clocksource got marked unstable
due to a large difference in the TSC value. I'm not sure if the guest
run for a long time with disabled interrupts or if the host was very
busy and didn't schedule the guest for some time.

I took a look on the qemu/KVM options and decided to update the options:

- Use kvm{32|64} as CPU. We could probably use `host' (like ARM does)
  for maximum available features but since we don't run any userland I'm
  not sure if it makes any difference.

- Drop the "noapic" option. There is no history why the APIC was disabled,
  I see no reason for it.  Once old qemu versions fade away, we can add
  "x2apic=on,tsc-deadline=on,hypervisor=on,tsc_adjust=on".

- Additional config options. It ensures that the kernel knowns that it
  runs as a kvm guest and can use virt devices like the kvm-clock as
  clocksource. The kvm-clock was the main motivation here.

- I didn't add a random HW device. It would make the random device ready
  earlier (not it doesn't complete the initialisation at all) but I
  doubt that there is any need for this.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
[ paulmck: The world is not quite ready for CONFIG_PARAVIRT_SPINLOCKS=y
  and x2apic, so they are omitted for the time being. ]
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
---
 tools/testing/selftests/rcutorture/bin/functions.sh | 13 ++++++++++++-
 .../selftests/rcutorture/configs/rcu/CFcommon       |  3 +++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rcutorture/bin/functions.sh b/tools/testing/selftests/rcutorture/bin/functions.sh
index 6bcb8b5b2ff2..c3a49fb4d6f6 100644
--- a/tools/testing/selftests/rcutorture/bin/functions.sh
+++ b/tools/testing/selftests/rcutorture/bin/functions.sh
@@ -172,7 +172,7 @@ identify_qemu_append () {
 	local console=ttyS0
 	case "$1" in
 	qemu-system-x86_64|qemu-system-i386)
-		echo noapic selinux=0 initcall_debug debug
+		echo selinux=0 initcall_debug debug
 		;;
 	qemu-system-aarch64)
 		console=ttyAMA0
@@ -191,8 +191,19 @@ identify_qemu_append () {
 # Output arguments for qemu arguments based on the TORTURE_QEMU_MAC
 # and TORTURE_QEMU_INTERACTIVE environment variables.
 identify_qemu_args () {
+	local KVM_CPU=""
+	case "$1" in
+	qemu-system-x86_64)
+		KVM_CPU=kvm64
+		;;
+	qemu-system-i386)
+		KVM_CPU=kvm32
+		;;
+	esac
 	case "$1" in
 	qemu-system-x86_64|qemu-system-i386)
+		echo -machine q35,accel=kvm
+		echo -cpu ${KVM_CPU}
 		;;
 	qemu-system-aarch64)
 		echo -machine virt,gic-version=host -cpu host
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/CFcommon b/tools/testing/selftests/rcutorture/configs/rcu/CFcommon
index d2d2a86139db..e19a444a0684 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/CFcommon
+++ b/tools/testing/selftests/rcutorture/configs/rcu/CFcommon
@@ -1,2 +1,5 @@
 CONFIG_RCU_TORTURE_TEST=y
 CONFIG_PRINTK_TIME=y
+CONFIG_HYPERVISOR_GUEST=y
+CONFIG_PARAVIRT=y
+CONFIG_KVM_GUEST=y
-- 
2.17.1