[PATCH V10 12/19] RISC-V: paravirt: pvqspinlock: Add nopvspin kernel parameter

guoren
2023-08-02T16:51:04Z

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

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 2 +-
arch/riscv/kernel/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 de6b7ee752cd..1a8878f6bfbd 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3820,7 +3820,7 @@
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/paravirt.c b/arch/riscv/kernel/paravirt.c
index 1bacb2cf3872..b55c3d3c0c17 100644
--- a/arch/riscv/kernel/paravirt.c
+++ b/arch/riscv/kernel/paravirt.c
@@ -165,8 +165,21 @@ DEFINE_STATIC_CALL(pv_queued_spin_unlock, native_queued_spin_unlock);
EXPORT_SYMBOL(__SCK__pv_queued_spin_lock_slowpath);
EXPORT_SYMBOL(__SCK__pv_queued_spin_unlock);

+static bool nopvspin;
+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;