From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3v1WDK3JQmzDqHZ for ; Sun, 15 Jan 2017 20:25:04 +1100 (AEDT) Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v0F9NnjP094913 for ; Sun, 15 Jan 2017 04:25:02 -0500 Received: from e31.co.us.ibm.com (e31.co.us.ibm.com [32.97.110.149]) by mx0b-001b2d01.pphosted.com with ESMTP id 27yjxrdtkv-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Sun, 15 Jan 2017 04:25:02 -0500 Received: from localhost by e31.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 15 Jan 2017 02:25:01 -0700 Date: Sun, 15 Jan 2017 01:24:54 -0800 From: "Paul E. McKenney" To: Ingo Molnar 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 Reply-To: paulmck@linux.vnet.ibm.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> <20170115075711.GA19506@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170115075711.GA19506@gmail.com> Message-Id: <20170115092454.GF5238@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, Jan 15, 2017 at 08:57:11AM +0100, Ingo Molnar wrote: > > * 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. I already have the patch queued, so how about I keep it if I get an ack from the powerpc guys and drop it otherwise? Thanx, Paul