linux-kernel - Re: [PATCH] locking/osq: Drop the overload of osq lock

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Message-ID: <20160627075522.GT30154@twins.programming.kicks-ass.net>
Date:	Mon, 27 Jun 2016 09:55:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	panxinhui <xinhui@...ux.vnet.ibm.com>
Cc:	Boqun Feng <boqun.feng@...il.com>,
	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...hat.com, dave@...olabs.net,
	will.deacon@....com, Waiman.Long@....com, benh@...nel.crashing.org
Subject: Re: [PATCH] locking/osq: Drop the overload of osq lock

On Sun, Jun 26, 2016 at 12:59:01PM +0800, panxinhui wrote:
> 
> > 在 2016年6月26日，03:12，Peter Zijlstra <peterz@...radead.org> 写道：
> > 
> > On Sun, Jun 26, 2016 at 01:27:51AM +0800, panxinhui wrote:
> > 
> >> by the way I still think mutex_unlock has a big overload too. 
> > 
> > Do you mean overhead?
> > 
> oh, maybe you are right. 

> mutex_unlock ’s implementation uses inc_return variant on  ppc, and
> that’s expensive. I am thinking of using  cmpxchg instead. 

That statement doesn't make any sense. PPC is an LL/SC arch, inc_return
and cmpxchg are the 'same' LL/SC loop.