Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier
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- To: Boqun Feng <boqun.feng@xxxxxxxxx>
- Subject: Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier
- From: Will Deacon <will.deacon@xxxxxxx>
- Date: Mon, 20 Jun 2016 08:59:00 +0100
- Cc: Waiman Long <waiman.long@xxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, linux-alpha@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, Davidlohr Bueso <dave@xxxxxxxxxxxx>, Jason Low <jason.low2@xxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Scott J Norton <scott.norton@xxxxxxx>, Douglas Hatch <doug.hatch@xxxxxxx>
- In-reply-to: <20160618084620.GA24424@insomnia>
- List-id: <linux-ia64.vger.kernel.org>
- References: <1465944489-43440-2-git-send-email-Waiman.Long@hpe.com> <20160615080446.GA28443@insomnia> <5761A5FF.5070703@hpe.com> <20160616021951.GA16918@insomnia> <57631BBA.9070505@hpe.com> <20160617004837.GB16918@insomnia> <576416B1.6020006@hpe.com> <20160617154536.GB1284@arm.com> <57643EB7.6030600@hpe.com> <20160618084620.GA24424@insomnia>
- User-agent: Mutt/1.5.23 (2014-03-12)
On Sat, Jun 18, 2016 at 04:46:20PM +0800, Boqun Feng wrote:
> On Fri, Jun 17, 2016 at 02:17:27PM -0400, Waiman Long wrote:
> > keep the xchg() function as it is or use smp_store_release(&next->locked,
> > 1). So which one is a better alternative for ARM or PPC?
> >
>
> For PPC, I think xchg_release() + smp_store_release() is better than the
> current code, because the former has two lwsync while the latter has two
> sync, and sync is quite expensive than lwsync on PPC.
>
> I need to leave the ARM part to Will ;-)
I doubt there's much in it, but xchg() has DMB + release, so xchg_release +
smp_store_release is probably slightly better for us too.
Will
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