linux-kernel - Re: [PATCH v4 3/4] locking/qspinlock: Add ARCH_USE_QUEUED_SPINLOCKS

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Date:   Wed, 7 Apr 2021 10:42:24 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Guo Ren <guoren@...nel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org,
        linux-arch <linux-arch@...r.kernel.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Anup Patel <anup@...infault.org>
Subject: Re: [PATCH v4 3/4] locking/qspinlock: Add
 ARCH_USE_QUEUED_SPINLOCKS_XCHG32

On Tue, Apr 06, 2021 at 09:15:50AM +0200, Peter Zijlstra wrote:
> Anyway, given you have such a crap architecture (and here I thought
> RISC-V was supposed to be a modern design *sigh*), you had better go
> look at the sparc64 atomic implementation which has a software backoff
> for failed CAS in order to make fwd progress.

It wasn't supposed to be modern.  It was supposed to use boring old
ideas.  Where it actually did that it is a great ISA, in parts where
academics actually tried to come up with cool or state of the art
ideas (interrupt handling, tlb shootdowns, the totally fucked up
memory model) it turned into a trainwreck.