linux-kernel - Re: [PATCH] riscv: locks: introduce ticket-based spinlock implementation

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Message-ID: <YFsvTXg07U+Adsto@hirez.programming.kicks-ass.net>
Date:   Wed, 24 Mar 2021 13:23:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vitaly Wool <vitaly.wool@...sulko.com>
Cc:     guoren@...nel.org, linux-riscv <linux-riscv@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Anup Patel <anup@...infault.org>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] riscv: locks: introduce ticket-based spinlock
 implementation

On Wed, Mar 24, 2021 at 12:15:47PM +0100, Vitaly Wool wrote:
> On Wed, Mar 24, 2021, 11:16 AM <guoren@...nel.org> wrote:
> 
> > From: Guo Ren <guoren@...ux.alibaba.com>
> >
> > This patch introduces a ticket lock implementation for riscv, along the
> > same lines as the implementation for arch/arm & arch/csky.
> >
> 
> Could you please provide a rationale for this? Like, what is wrong with the
> current implementation.

test-and-set spinlocks have terrible worst case behaviour.