linux-kernel - Re: [PATCH V2 16/19] csky: SMP support

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Message-ID: <20180706093932.GT2476@hirez.programming.kicks-ass.net>
Date:   Fri, 6 Jul 2018 11:39:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Guo Ren <ren_guo@...ky.com>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, daniel.lezcano@...aro.org,
        jason@...edaemon.net, arnd@...db.de, c-sky_gcc_upstream@...ky.com,
        gnu-csky@...tor.com, thomas.petazzoni@...tlin.com,
        wbx@...ibc-ng.org, green.hu@...il.com,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH V2 16/19] csky: SMP support

On Fri, Jul 06, 2018 at 02:07:40PM +0800, Guo Ren wrote:

> > Please explain those mb()'s... I'm thinking you meant to use smp_mb().
> Yes, smp_mb(). Current smp_mb()&mb() is the same: sync.is.
> 
> In next version patch, I'll seperate smp_mb() and mb() and use ld/st.barrier
> instead of sync.is. Sync.is is expensive that it flush cpu's pipeline.

I'll second my own call for documentation, because now there's three
memory ordering instructions:

 "SYNC", "SYNC.IS" and "LD/ST.BARRIER"

None of which have yet been explained.