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

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Date: Mon, 25 Dec 2023 07:58:45 -0500
From: guoren@...nel.org
To: paul.walmsley@...ive.com,
	palmer@...belt.com,
	guoren@...nel.org,
	panqinglin2020@...as.ac.cn,
	bjorn@...osinc.com,
	conor.dooley@...rochip.com,
	leobras@...hat.com,
	peterz@...radead.org,
	anup@...infault.org,
	keescook@...omium.org,
	wuwei2016@...as.ac.cn,
	xiaoguang.xing@...hgo.com,
	chao.wei@...hgo.com,
	unicorn_wang@...look.com,
	uwu@...nowy.me,
	jszhang@...nel.org,
	wefu@...hat.com,
	atishp@...shpatra.org
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH V12 12/14] RISC-V: paravirt: pvqspinlock: Add nopvspin kernel parameter

From: Guo Ren <guoren@...ux.alibaba.com>

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

Reviewed-by: Leonardo Bras <leobras@...hat.com>
Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
---
 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