linux-kernel - Re: [PATCH] riscv: Add riscv_force_qspinlock for early

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Message-ID: <CAJF2gTRt0c78jPGN8ZX-u3dJKBrOkoV7VZQW2A+rVpuVOzdvLg@mail.gmail.com>
Date: Sun, 22 Dec 2024 12:03:57 +0800
From: Guo Ren <guoren@...nel.org>
To: Alexandre Ghiti <alex@...ti.fr>
Cc: conor@...nel.org, alexghiti@...osinc.com, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, paul.walmsley@...ive.com, palmer@...belt.com, 
	bjorn@...osinc.com, leobras@...hat.com, peterz@...radead.org, 
	parri.andrea@...il.com, longman@...hat.com, boqun.feng@...il.com, 
	arnd@...db.de, will@...nel.org, corbet@....net, 
	Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH] riscv: Add riscv_force_qspinlock for early_param

On Mon, Dec 16, 2024 at 5:15 PM Alexandre Ghiti <alex@...ti.fr> wrote:
>
> Hi Guo,
>
> On 14/12/2024 05:35, guoren@...nel.org wrote:
> > From: Guo Ren <guoren@...ux.alibaba.com>
> >
> > When CONFIG_RISCV_COMBO_SPINLOCKS is enabled, permit qspinlock
> > force enabled. See the Kconfig entry for RISCV_COMBO_SPINLOCKS.
> >
> > Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@...nel.org>
> > ---
> >   Documentation/admin-guide/kernel-parameters.txt |  5 +++++
> >   arch/riscv/kernel/setup.c                       | 13 ++++++++++++-
> >   2 files changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 3872bc6ec49d..43d0df2922b2 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -5887,6 +5887,11 @@
> >                       [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
> >                       CPUs.
> >
> > +     riscv_force_qspinlock [RISCV, EARLY]
> > +                     When CONFIG_RISCV_COMBO_SPINLOCKS is enabled, permit
> > +                     qspinlock force enabled. See the Kconfig entry for
> > +                     RISCV_COMBO_SPINLOCKS.
> > +
> >       riscv_isa_fallback [RISCV,EARLY]
> >                       When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
> >                       falling back to detecting extension support by parsing
> > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > index 45010e71df86..74b13bc64c9c 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -247,6 +247,15 @@ static void __init parse_dtb(void)
> >   #if defined(CONFIG_RISCV_COMBO_SPINLOCKS)
> >   DEFINE_STATIC_KEY_TRUE(qspinlock_key);
> >   EXPORT_SYMBOL(qspinlock_key);
> > +
> > +static bool force_qspinlock;
> > +
> > +static int __init riscv_force_qspinlock(char *p)
> > +{
> > +     force_qspinlock = true;
> > +     return 0;
> > +}
> > +early_param("riscv_force_qspinlock", riscv_force_qspinlock);
> >   #endif
> >
> >   static void __init riscv_spinlock_init(void)
> > @@ -267,7 +276,9 @@ static void __init riscv_spinlock_init(void)
> >               using_ext = "using Ziccrse";
> >       }
> >   #if defined(CONFIG_RISCV_COMBO_SPINLOCKS)
> > -     else {
> > +     else if (force_qspinlock) {
> > +             using_ext = "force";
> > +     } else {
> >               static_branch_disable(&qspinlock_key);
> >               pr_info("Ticket spinlock: enabled\n");
> >               return;
>
>
> What's the use case for this early param? To me that implies that a
> platform may have another extension which would allow the usage of
We want to use it for sg2042 & th1520. No new extension was
introduced, and some micro-architecture could give LR/SC
implementation a forward progress guarantee more than the spec
required.

> qspinlock, so why not listing it in riscv_spinlock_init() instead?
List all platforms in riscv_spinlock_init is noisy, maybe give a
qspinlock param in cmdline, and they could put it in their boot args.

>
> Thanks,
>
> Alex
>


-- 
Best Regards
 Guo Ren