From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lai Jiangshan Subject: Re: [PATCH] lglock: add read-preference local-global rwlock Date: Sat, 02 Mar 2013 21:42:15 +0800 Message-ID: <513201B7.5070004@cn.fujitsu.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130301182854.GA3631@redhat.com> Sender: linux-doc-owner@vger.kernel.org To: Oleg Nesterov , paulmck@linux.vnet.ibm.com Cc: "Srivatsa S. Bhat" , Lai Jiangshan , Michel Lespinasse , 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, 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 List-Id: linux-arch.vger.kernel.org On 02/03/13 02:28, Oleg Nesterov wrote: > Lai, I didn't read this discussion except the code posted by Michel. > I'll try to read this patch carefully later, but I'd like to ask > a couple of questions. > > This version looks more complex than Michel's, why? Just curious, I > am trying to understand what I missed. See > http://marc.info/?l=linux-kernel&m=136196350213593 Michel changed my old draft version a little, his version is good enough for me. My new version tries to add a little better nestable support with only adding single __this_cpu_op() in _read_[un]lock(). > > And I can't understand FALLBACK_BASE... > > OK, suppose that CPU_0 does _write_unlock() and releases ->fallback_rwlock. > > CPU_1 does _read_lock(), and ... > >> +void lg_rwlock_local_read_lock(struct lgrwlock *lgrw) >> +{ >> + struct lglock *lg = &lgrw->lglock; >> + >> + preempt_disable(); >> + rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_); >> + if (likely(!__this_cpu_read(*lgrw->reader_refcnt))) { >> + if (!arch_spin_trylock(this_cpu_ptr(lg->lock))) { > > _trylock() fails, > >> + read_lock(&lgrw->fallback_rwlock); >> + __this_cpu_add(*lgrw->reader_refcnt, FALLBACK_BASE); > > so we take ->fallback_rwlock and ->reader_refcnt == FALLBACK_BASE. > > CPU_0 does lg_global_unlock(lgrw->lglock) and finishes _write_unlock(). > > Interrupt handler on CPU_1 does _read_lock() notices ->reader_refcnt != 0 > and simply does this_cpu_inc(), so reader_refcnt == FALLBACK_BASE + 1. > > Then irq does _read_unlock(), and > >> +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw) >> +{ >> + switch (__this_cpu_dec_return(*lgrw->reader_refcnt)) { >> + case 0: >> + lg_local_unlock(&lgrw->lglock); >> + return; >> + case FALLBACK_BASE: >> + __this_cpu_sub(*lgrw->reader_refcnt, FALLBACK_BASE); >> + read_unlock(&lgrw->fallback_rwlock); > > hits this case? > > Doesn't look right, but most probably I missed something. Your are right, I just realized that I had spit a code which should be atomic. I hope this patch(V2) can get more reviews. My first and many locking knowledge is learned from Paul. Paul, would you also review it? Thanks, Lai > > Oleg. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([222.73.24.84]:8697 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752015Ab3CBNkQ (ORCPT ); Sat, 2 Mar 2013 08:40:16 -0500 Message-ID: <513201B7.5070004@cn.fujitsu.com> Date: Sat, 02 Mar 2013 21:42:15 +0800 From: Lai Jiangshan MIME-Version: 1.0 Subject: Re: [PATCH] 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> In-Reply-To: <20130301182854.GA3631@redhat.com> Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-arch-owner@vger.kernel.org List-ID: To: Oleg Nesterov , paulmck@linux.vnet.ibm.com Cc: "Srivatsa S. Bhat" , Lai Jiangshan , Michel Lespinasse , 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, 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 Message-ID: <20130302134215.kO9OLk_RHTBr3Kj0Lwi-Ipe2CYtVSgwyxPhWI8w9sxA@z> On 02/03/13 02:28, Oleg Nesterov wrote: > Lai, I didn't read this discussion except the code posted by Michel. > I'll try to read this patch carefully later, but I'd like to ask > a couple of questions. > > This version looks more complex than Michel's, why? Just curious, I > am trying to understand what I missed. See > http://marc.info/?l=linux-kernel&m=136196350213593 Michel changed my old draft version a little, his version is good enough for me. My new version tries to add a little better nestable support with only adding single __this_cpu_op() in _read_[un]lock(). > > And I can't understand FALLBACK_BASE... > > OK, suppose that CPU_0 does _write_unlock() and releases ->fallback_rwlock. > > CPU_1 does _read_lock(), and ... > >> +void lg_rwlock_local_read_lock(struct lgrwlock *lgrw) >> +{ >> + struct lglock *lg = &lgrw->lglock; >> + >> + preempt_disable(); >> + rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_); >> + if (likely(!__this_cpu_read(*lgrw->reader_refcnt))) { >> + if (!arch_spin_trylock(this_cpu_ptr(lg->lock))) { > > _trylock() fails, > >> + read_lock(&lgrw->fallback_rwlock); >> + __this_cpu_add(*lgrw->reader_refcnt, FALLBACK_BASE); > > so we take ->fallback_rwlock and ->reader_refcnt == FALLBACK_BASE. > > CPU_0 does lg_global_unlock(lgrw->lglock) and finishes _write_unlock(). > > Interrupt handler on CPU_1 does _read_lock() notices ->reader_refcnt != 0 > and simply does this_cpu_inc(), so reader_refcnt == FALLBACK_BASE + 1. > > Then irq does _read_unlock(), and > >> +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw) >> +{ >> + switch (__this_cpu_dec_return(*lgrw->reader_refcnt)) { >> + case 0: >> + lg_local_unlock(&lgrw->lglock); >> + return; >> + case FALLBACK_BASE: >> + __this_cpu_sub(*lgrw->reader_refcnt, FALLBACK_BASE); >> + read_unlock(&lgrw->fallback_rwlock); > > hits this case? > > Doesn't look right, but most probably I missed something. Your are right, I just realized that I had spit a code which should be atomic. I hope this patch(V2) can get more reviews. My first and many locking knowledge is learned from Paul. Paul, would you also review it? Thanks, Lai > > Oleg. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >