From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x241.google.com (mail-wm0-x241.google.com [IPv6:2a00:1450:400c:c09::241]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3v1TH311CjzDqVn for ; Sun, 15 Jan 2017 18:57:19 +1100 (AEDT) Received: by mail-wm0-x241.google.com with SMTP id d140so6180598wmd.2 for ; Sat, 14 Jan 2017 23:57:18 -0800 (PST) Sender: Ingo Molnar Date: Sun, 15 Jan 2017 08:57:11 +0100 From: Ingo Molnar To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, will.deacon@arm.com, boqun.feng@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, Peter Zijlstra Subject: Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering Message-ID: <20170115075711.GA19506@gmail.com> References: <20170114091941.GA22961@linux.vnet.ibm.com> <1484385601-23379-2-git-send-email-paulmck@linux.vnet.ibm.com> <20170114093550.GB14970@gmail.com> <20170114195417.GW5238@linux.vnet.ibm.com> <20170114214159.GA7098@linux.vnet.ibm.com> <20170115071123.GB26581@gmail.com> <20170115074034.GE5238@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170115074034.GE5238@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , * Paul E. McKenney wrote: > On Sun, Jan 15, 2017 at 08:11:23AM +0100, Ingo Molnar wrote: > > > > * Paul E. McKenney wrote: > > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > > index 357b32aaea48..5fdfe874229e 100644 > > > --- a/include/linux/rcupdate.h > > > +++ b/include/linux/rcupdate.h > > > @@ -1175,11 +1175,11 @@ do { \ > > > * if the UNLOCK and LOCK are executed by the same CPU or if the > > > * UNLOCK and LOCK operate on the same lock variable. > > > */ > > > -#ifdef CONFIG_PPC > > > +#ifdef CONFIG_ARCH_WEAK_RELACQ > > > #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ > > > -#else /* #ifdef CONFIG_PPC */ > > > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > #define smp_mb__after_unlock_lock() do { } while (0) > > > -#endif /* #else #ifdef CONFIG_PPC */ > > > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > > > > > > > > So at the risk of sounding totally pedantic, why not structure it like the > > existing smp_mb__before/after*() primitives in barrier.h? > > > > That allows asm-generic/barrier.h to pick up the definition - for example in the > > case of smp_acquire__after_ctrl_dep() we do: > > > > #ifndef smp_acquire__after_ctrl_dep > > #define smp_acquire__after_ctrl_dep() smp_rmb() > > #endif > > > > Which allows Tile to relax it: > > > > arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep() barrier() > > > > I.e. I'd move the API definition out of rcupdate.h and into barrier.h - even > > though tree-RCU is the only user of this barrier type. > > I wouldn't have any problem with that, however, some time back it was > moved into RCU because (you guessed it!) RCU is the only user. ;-) Indeed ... [sounds of rummaging around in the Git tree] I found this commit of yours from ancient history (more than a year ago!): commit 12d560f4ea87030667438a169912380be00cea4b Author: Paul E. McKenney Date: Tue Jul 14 18:35:23 2015 -0700 rcu,locking: Privatize smp_mb__after_unlock_lock() RCU is the only thing that uses smp_mb__after_unlock_lock(), and is likely the only thing that ever will use it, so this commit makes this macro private to RCU. Signed-off-by: Paul E. McKenney Cc: Will Deacon Cc: Peter Zijlstra Cc: Benjamin Herrenschmidt Cc: "linux-arch@vger.kernel.org" So I concur and I'm fine with your patch - or with the status quo code as well. Thanks, Ingo