From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757555Ab3CER5b (ORCPT ); Tue, 5 Mar 2013 12:57:31 -0500 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:53019 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754892Ab3CER53 (ORCPT ); Tue, 5 Mar 2013 12:57:29 -0500 Message-ID: <51363179.2030109@linux.vnet.ibm.com> Date: Tue, 05 Mar 2013 23:25:05 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 MIME-Version: 1.0 To: Lai Jiangshan CC: Michel Lespinasse , Oleg Nesterov , Lai Jiangshan , linux-doc@vger.kernel.org, peterz@infradead.org, fweisbec@gmail.com, linux-kernel@vger.kernel.org, namhyung@kernel.org, mingo@kernel.org, linux-arch@vger.kernel.org, linux@arm.linux.org.uk, xiaoguangrong@linux.vnet.ibm.com, wangyun@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, rusty@rustcorp.com.au, rostedt@goodmis.org, rjw@sisk.pl, vincent.guittot@linaro.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, sbw@mit.edu, tj@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH V2] lglock: add read-preference local-global rwlock References: <512BBAD8.8010006@linux.vnet.ibm.com> <512C7A38.8060906@linux.vnet.ibm.com> <512CC509.1050000@linux.vnet.ibm.com> <512D0D67.9010609@linux.vnet.ibm.com> <512E7879.20109@linux.vnet.ibm.com> <5130E8E2.50206@cn.fujitsu.com> <20130301182854.GA3631@redhat.com> <5131FB4C.7070408@cn.fujitsu.com> <513232B6.9060905@linux.vnet.ibm.com> <5136123C.3040508@cn.fujitsu.com> In-Reply-To: <5136123C.3040508@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13030517-2000-0000-0000-00000B2F48C1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/05/2013 09:11 PM, Lai Jiangshan wrote: > On 03/03/13 01:11, Srivatsa S. Bhat wrote: >> On 03/02/2013 06:44 PM, Lai Jiangshan wrote: >>> From 345a7a75c314ff567be48983e0892bc69c4452e7 Mon Sep 17 00:00:00 2001 >>> From: Lai Jiangshan >>> Date: Sat, 2 Mar 2013 20:33:14 +0800 >>> Subject: [PATCH] lglock: add read-preference local-global rwlock >>> >>> Current lglock is not read-preference, so it can't be used on some cases >>> which read-preference rwlock can do. Example, get_cpu_online_atomic(). >>> >> [...] >>> diff --git a/kernel/lglock.c b/kernel/lglock.c >>> index 6535a66..52e9b2c 100644 >>> --- a/kernel/lglock.c >>> +++ b/kernel/lglock.c >>> @@ -87,3 +87,71 @@ void lg_global_unlock(struct lglock *lg) >>> preempt_enable(); >>> } >>> EXPORT_SYMBOL(lg_global_unlock); >>> + >>> +#define FALLBACK_BASE (1UL << 30) >>> + >>> +void lg_rwlock_local_read_lock(struct lgrwlock *lgrw) >>> +{ >>> + struct lglock *lg = &lgrw->lglock; >>> + >>> + preempt_disable(); >>> + if (likely(!__this_cpu_read(*lgrw->reader_refcnt))) { >>> + rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_); >>> + if (unlikely(!arch_spin_trylock(this_cpu_ptr(lg->lock)))) { >>> + read_lock(&lgrw->fallback_rwlock); >>> + __this_cpu_write(*lgrw->reader_refcnt, FALLBACK_BASE); >>> + return; >>> + } >>> + } >>> + >>> + __this_cpu_inc(*lgrw->reader_refcnt); >>> +} >>> +EXPORT_SYMBOL(lg_rwlock_local_read_lock); >>> + >>> +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw) >>> +{ >>> + switch (__this_cpu_read(*lgrw->reader_refcnt)) { >>> + case 1: >>> + __this_cpu_write(*lgrw->reader_refcnt, 0); >>> + lg_local_unlock(&lgrw->lglock); >>> + return; >> >> This should be a break, instead of a return, right? >> Otherwise, there will be a preempt imbalance... > > > "lockdep" and "preempt" are handled in lg_local_unlock(&lgrw->lglock); > Ah, ok.. I had missed that. Regards, Srivatsa S. Bhat