linux-kernel - Re: [PATCH powerpc/next v6 0/4] atomics: powerpc: Implement relaxed/acquire/release variants

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Date:	Mon, 28 Dec 2015 08:30:29 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@...com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH powerpc/next v6 0/4] atomics: powerpc: Implement
 relaxed/acquire/release variants

On Sun, Dec 27, 2015 at 06:53:39PM +1100, Michael Ellerman wrote:
> On Wed, 2015-12-23 at 18:54 +0800, Boqun Feng wrote:
> > On Wed, Dec 23, 2015 at 01:40:05PM +1100, Michael Ellerman wrote:
> > > On Tue, 2015-12-15 at 22:24 +0800, Boqun Feng wrote:
> > > > Hi all,
> > > > 
> > > > This is v6 of the series.
> > > > 
> > > > Link for v1: https://lkml.org/lkml/2015/8/27/798
> > > > Link for v2: https://lkml.org/lkml/2015/9/16/527
> > > > Link for v3: https://lkml.org/lkml/2015/10/12/368
> > > > Link for v4: https://lkml.org/lkml/2015/10/14/670
> > > > Link for v5: https://lkml.org/lkml/2015/10/26/141
> > > > 
> > > > 
> > > > Changes since v5:
> > > > 
> > > > *	rebase on the next branch of powerpc.
> > > > 
> > > > *	pull two fix and one testcase patches out, which are already
> > > > 	sent separately
> > > > 
> > > > *	some clean up or code format fixing.
> > > > 
> > > > 
> > > > Paul, Peter and Will, thank you for your comments and suggestions in the review
> > > > of previous versions. From this version on, This series is against the next
> > > > branch of powerpc tree, because most of the code touch arch/powerpc/*.
> > > 
> > > 
> > > Sorry if we already discussed this, but did we decide how we were going to
> > > merge this? There's the one patch to generic code and then three powerpc
> > > patches.
> > > 
> > > It'd make most sense for it to go via powerpc I think. Given that the change to
> > > generic code is relatively trivial I'll plan to merge this unless someone
> > > objects.
> > > 
> > > Also it is pretty late in the -next cycle for something like this. But AFAICS
> > > there are no users of these "atomic*relaxed" variants yet other than arm64 code
> > > and qspinlocks, neither of which are used on powerpc. So adding them should be
> > > pretty harmless.
> > > 
> > 
> > There is one thing we should be aware of, that is the bug:
> > 
> > http://lkml.kernel.org/r/5669D5F2.5050004@caviumnetworks.com
> > 
> > which though has been fixed by:
> > 
> > http://lkml.kernel.org/r/20151217160549.GH6344@twins.programming.kicks-ass.net
> > 
> > but the fix is not in powerpc/next right now. As this patchset makes
> > atomic_xchg_acquire a real ACQUIRE, so we will also trigger that bug if
> > this series gets merged in the next branch of powerpc tree, though
> > that's not the problem of this patchset.
> > 
> > Not sure whether this is a problem for your maintence, but just think
> > it's better to make you aware of this ;-)
> 
> Yes that's pretty important thank you :)
> 
> It's not so much that bug that's important, but the fact that I completely
> forget about the acquire/release implementations. Those are used already in
> mainline and so we don't want to add implementations this late in the cycle
> without wider testing.
> 

Understood.

> So I'll have to push this series until 4.6 so it can get some time in -next.
> Sorry!
> 

That's fine, thank you!

Regards,
Boqun

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