[PATCH V11 12/17] RISC-V: paravirt: pvqspinlock: Add nopvspin kernel parameter

[Guo Ren]

On Fri, Sep 15, 2023 at 2:05 PM Leonardo Bras <leobras at redhat.com> wrote:
>
> On Sun, Sep 10, 2023 at 04:29:06AM -0400, guoren at kernel.org wrote:
> > From: Guo Ren <guoren at linux.alibaba.com>
> >
> > 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 at linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren at kernel.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 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;
Okay.

>
> Other than that, LGTM:
> Reviewed-by: Leonardo Bras <leobras at redhat.com>
>
> 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
> >
>


-- 
Best Regards
 Guo Ren