linux-kernel - Re: [PATCH 2/5] riscv: Add QUEUED_SPINLOCKS & QUEUED

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Message-ID: <20201125141813.GC2414@hirez.programming.kicks-ass.net>
Date:   Wed, 25 Nov 2020 15:18:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Guo Ren <guoren@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>,
        Michael Clark <michaeljclark@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 2/5] riscv: Add QUEUED_SPINLOCKS & QUEUED_RWLOCKS
 supported

On Wed, Nov 25, 2020 at 08:52:23AM +0800, Guo Ren wrote:

> > I'm pretty sure there's a handfull of implementations like this out
> > there... if only we could share.
> Michael has sent qspinlock before, ref to Link below. He reused mips' code.
> 
> Link: https://lore.kernel.org/linux-riscv/20190211043829.30096-1-michaeljclark@mac.com/
> 
> Which short xchg implementation do you prefer (Mine or his)?

Well, it would be very nice to have mips/riscv/csky all use the same
header to implement these I suppose.

But then we're back to a cmpxchg-loop, in which case Arnd's suggestion
isn't worse.