From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750965AbdAOHkp (ORCPT ); Sun, 15 Jan 2017 02:40:45 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:37962 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750849AbdAOHko (ORCPT ); Sun, 15 Jan 2017 02:40:44 -0500 Date: Sat, 14 Jan 2017 23:40:34 -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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170115071123.GB26581@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17011507-0016-0000-0000-000005DFD11F X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006436; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000199; SDB=6.00807778; UDB=6.00393328; IPR=6.00585136; BA=6.00005056; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013924; XFM=3.00000011; UTC=2017-01-15 07:40:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17011507-0017-0000-0000-000036812D24 Message-Id: <20170115074034.GE5238@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-01-15_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1612050000 definitions=main-1701150118 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. ;-) Thanx, Paul