linux-kernel - Re: [PATCH 8/9] RISC-V: User-facing API

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Date:   Thu, 6 Jul 2017 08:34:27 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Palmer Dabbelt <palmer@...belt.com>, peterz@...radead.org,
        mingo@...hat.com, mcgrof@...nel.org, viro@...iv.linux.org.uk,
        sfr@...b.auug.org.au, nicolas.dichtel@...nd.com,
        rmk+kernel@...linux.org.uk, msalter@...hat.com,
        tklauser@...tanz.ch, james.hogan@...tec.com,
        paul.gortmaker@...driver.com, linux@...ck-us.net,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        albert@...ive.com, patches@...ups.riscv.org,
        mathieu.desnoyers@...icios.com
Subject: Re: [PATCH 8/9] RISC-V: User-facing API

On Thu, Jul 06, 2017 at 09:55:03AM +0100, Will Deacon wrote:
> Agreed on the indirection; it feels like this is something that should be in
> the vDSO, which could use the cmpxchg instruction if it's available, or
> otherwise just uses plain loads and stores.

Even that seems like a lot of indirection for something that is in
the critical fast path for synchronization.  I really can't understand
how a new ISA / ABI could even come up with an idea as stupid as making
essential synchronization primitives optional.