linux-kernel - Re: [PATCH V5] riscv: Add qspinlock support

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Message-ID: <CAJF2gTSQ17YQ41G+e0TBp2njPzx4LBGZw0GhyKCBqDW5AAuYaw@mail.gmail.com>
Date:   Tue, 21 Jun 2022 06:47:56 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Palmer Dabbelt <palmer@...osinc.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V5] riscv: Add qspinlock support

On Tue, Jun 21, 2022 at 5:16 AM Waiman Long <longman@...hat.com> wrote:
>
>
> On 6/20/22 16:42, Arnd Bergmann wrote:
> > On Mon, Jun 20, 2022 at 5:54 PM <guoren@...nel.org> 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.
RISC-V has had NUMA scenario. Think two AI chips with CCIX ports, they
could be flexibly connected when needed.

>
> Cheers,
> Longman
>


-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/