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

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Message-ID: <20170706154512.GD15574@arm.com>
Date:   Thu, 6 Jul 2017 16:45:13 +0100
From:   Will Deacon <will.deacon@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     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 08:34:27AM -0700, Christoph Hellwig wrote:
> 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. 

No disagreement there!

Will