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

From: Leonardo Bras <leobras@redhat.com>
To: Guo Ren <guoren@kernel.org>
Cc: paul.walmsley@sifive.com, anup@brainfault.org,
	peterz@infradead.org, mingo@redhat.com, will@kernel.org,
	palmer@rivosinc.com, longman@redhat.com, boqun.feng@gmail.com,
	tglx@linutronix.de, paulmck@kernel.org, rostedt@goodmis.org,
	rdunlap@infradead.org, catalin.marinas@arm.com,
	conor.dooley@microchip.com, xiaoguang.xing@sophgo.com,
	bjorn@rivosinc.com, alexghiti@rivosinc.com,
	keescook@chromium.org, greentime.hu@sifive.com,
	ajones@ventanamicro.com, jszhang@kernel.org, wefu@redhat.com,
	wuwei2016@iscas.ac.cn, linux-arch@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-doc@vger.kernel.org,
	kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	linux-csky@vger.kernel.org, Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH V11 12/17] RISC-V: paravirt: pvqspinlock: Add nopvspin kernel parameter
Date: Tue, 19 Sep 2023 02:44:38 -0300	[thread overview]
Message-ID: <ZQk1Ri1DrchrrFLw@redhat.com> (raw)
In-Reply-To: <CAJF2gTQMNu7PXf3JT-nZt1+jp6osqERUvnvEexjK+Ak=ahxcUA@mail.gmail.com>

On Sun, Sep 17, 2023 at 11:03:30PM +0800, Guo Ren wrote:
> On Fri, Sep 15, 2023 at 2:05 PM Leonardo Bras <leobras@redhat.com> wrote:
> >
> > On Sun, Sep 10, 2023 at 04:29:06AM -0400, guoren@kernel.org wrote:
> > > From: Guo Ren <guoren@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@linux.alibaba.com>
> > > Signed-off-by: Guo Ren <guoren@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.

Thx!
Leo

> 
> >
> > Other than that, LGTM:
> > Reviewed-by: Leonardo Bras <leobras@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
> 