On Sun, Sep 10, 2023 at 04:29:06AM -0400, guoren@xxxxxxxxxx wrote:
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> 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@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 f75bedc50e00..e74aed631573 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3857,7 +3857,7 @@
> 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 85ff5a3ec234..a0ad4657f437 100644
> --- a/arch/riscv/kernel/qspinlock_paravirt.c
> +++ b/arch/riscv/kernel/qspinlock_paravirt.c
> @@ -41,8 +41,21 @@ 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;
It is only used in init, so it makes sense to add __initdata.
static bool nopvspin __initdata;
Other than that, LGTM:
Reviewed-by: Leonardo Bras <leobras@xxxxxxxxxx>
Thanks!
Leo
> +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;
>
> --
> 2.36.1
>
