[PATCH V12 12/14] RISC-V: paravirt: pvqspinlock: Add nopvspin kernel parameter

[guoren]

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

Disables the qspinlock slow path using PV optimizations which
allow the hypervisor to 'idle' the guest on lock contention.

Reviewed-by: Leonardo Bras <leobras@xxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 +-
 arch/riscv/kernel/qspinlock_paravirt.c          | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b7794c96d91e..4aff81d741e2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3927,7 +3927,7 @@
 			as generic guest with no PV drivers. Currently support
 			XEN HVM, KVM, HYPER_V and VMWARE guest.
 
-	nopvspin	[X86,XEN,KVM]
+	nopvspin	[X86,XEN,KVM,RISC-V]
 			Disables the qspinlock slow path using PV optimizations
 			which allow the hypervisor to 'idle' the guest on lock
 			contention.
diff --git a/arch/riscv/kernel/qspinlock_paravirt.c b/arch/riscv/kernel/qspinlock_paravirt.c
index 7d1b99412222..4b04c93c4b9b 100644
--- a/arch/riscv/kernel/qspinlock_paravirt.c
+++ b/arch/riscv/kernel/qspinlock_paravirt.c
@@ -43,8 +43,21 @@ EXPORT_STATIC_CALL(pv_queued_spin_lock_slowpath);
 DEFINE_STATIC_CALL(pv_queued_spin_unlock, native_queued_spin_unlock);
 EXPORT_STATIC_CALL(pv_queued_spin_unlock);
 
+static bool nopvspin __initdata;
+static __init int parse_nopvspin(char *arg)
+{
+       nopvspin = true;
+       return 0;
+}
+early_param("nopvspin", parse_nopvspin);
+
 void __init pv_qspinlock_init(void)
 {
+	if (nopvspin) {
+		pr_info("PV qspinlocks disabled\n");
+		return;
+	}
+
 	if (num_possible_cpus() == 1)
 		return;
 
-- 
2.40.1