Re: [PATCH V5] riscv: Add qspinlock support

[Waiman Long]

On 6/20/22 16:42, Arnd Bergmann wrote:
> On Mon, Jun 20, 2022 at 5:54 PM <guoren@xxxxxxxxxx> wrote:
> > > +config RISCV_USE_QUEUED_SPINLOCKS
> > +       bool "Using queued spinlock instead of ticket-lock"
> Maybe we can just make ARCH_USE_QUEUED_SPINLOCKS
> user visible and give users the choice between the two generic
> implementations across all architectures that support the qspinlock
> variant.
>
> In arch/riscv, you'd then just have a
>
>          select ARCH_HAVE_QUEUED_SPINLOCKS
>
> diff --git a/arch/riscv/include/asm/spinlock.h
> b/arch/riscv/include/asm/spinlock.h
> > new file mode 100644
> > index 000000000000..fd3fd09cff52
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/spinlock.h
> > @@ -0,0 +1,12 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __ASM_SPINLOCK_H
> > +#define __ASM_SPINLOCK_H
> > +
> > +#ifdef CONFIG_ARCH_USE_QUEUED_SPINLOCKS
> > +#include <asm/qspinlock.h>
> > +#include <asm/qrwlock.h>
> > +#else
> > +#include <asm-generic/spinlock.h>
> > +#endif
> > +
> Along the same lines:
>
> I think I'd prefer the header changes to be done in the asm-generic
> version of this file, so this can be shared across all architectures
> that want to give the choice between ticket and queued spinlock.

I concur. Qspinlock is only needed if we want to support systems with a 
large number of CPUs. For systems with a small number of CPUs. It 
doesn't matter if qspinlock or the ticket lock is being used.

Cheers,
Longman