From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757692Ab3CEQkU (ORCPT ); Tue, 5 Mar 2013 11:40:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:19674 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757402Ab3CEQkR (ORCPT ); Tue, 5 Mar 2013 11:40:17 -0500 Date: Tue, 5 Mar 2013 17:35:22 +0100 From: Oleg Nesterov To: Lai Jiangshan Cc: Michel Lespinasse , "Srivatsa S. Bhat" , 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] lglock: add read-preference local-global rwlock Message-ID: <20130305163522.GA4179@redhat.com> References: <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> <20130302170656.GB29769@redhat.com> <51361540.3060603@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51361540.3060603@cn.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/05, Lai Jiangshan wrote: > > On 03/03/13 01:06, Oleg Nesterov wrote: > > On 03/02, Michel Lespinasse wrote: > >> > >> My version would be slower if it needs to take the > >> slow path in a reentrant way, but I'm not sure it matters either :) > > > > I'd say, this doesn't matter at all, simply because this can only happen > > if we race with the active writer. > > It can also happen when interrupted. (still very rarely) > > arch_spin_trylock() > ------->interrupted, > __this_cpu_read() returns 0. > arch_spin_trylock() fails > slowpath, any nested will be slowpath too. > ... > ..._read_unlock() > <-------interrupt > __this_cpu_inc() > .... Yes sure. Or it can take the local lock after we already take the global fallback_lock. But the same can happen with FALLBACK_BASE, just because we need to take a lock (local or global) first, then increment the counter. > (I worries to much. I tend to remove FALLBACK_BASE now, we should > add it only after we proved we needed it, this part is not proved) Agreed, great ;) Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH] lglock: add read-preference local-global rwlock Date: Tue, 5 Mar 2013 17:35:22 +0100 Message-ID: <20130305163522.GA4179@redhat.com> References: <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> <20130302170656.GB29769@redhat.com> <51361540.3060603@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Lai Jiangshan , linux-doc@vger.kernel.org, peterz@infradead.org, fweisbec@gmail.com, Michel Lespinasse , 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, namhyung@kernel.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, vincent.guittot@linaro.org, sbw@mit.edu, "Srivatsa S. Bhat" , tj@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org To: Lai Jiangshan Return-path: Content-Disposition: inline In-Reply-To: <51361540.3060603@cn.fujitsu.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Sender: "Linuxppc-dev" List-Id: netdev.vger.kernel.org On 03/05, Lai Jiangshan wrote: > > On 03/03/13 01:06, Oleg Nesterov wrote: > > On 03/02, Michel Lespinasse wrote: > >> > >> My version would be slower if it needs to take the > >> slow path in a reentrant way, but I'm not sure it matters either :) > > > > I'd say, this doesn't matter at all, simply because this can only happen > > if we race with the active writer. > > It can also happen when interrupted. (still very rarely) > > arch_spin_trylock() > ------->interrupted, > __this_cpu_read() returns 0. > arch_spin_trylock() fails > slowpath, any nested will be slowpath too. > ... > ..._read_unlock() > <-------interrupt > __this_cpu_inc() > .... Yes sure. Or it can take the local lock after we already take the global fallback_lock. But the same can happen with FALLBACK_BASE, just because we need to take a lock (local or global) first, then increment the counter. > (I worries to much. I tend to remove FALLBACK_BASE now, we should > add it only after we proved we needed it, this part is not proved) Agreed, great ;) Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 From: oleg@redhat.com (Oleg Nesterov) Date: Tue, 5 Mar 2013 17:35:22 +0100 Subject: [PATCH] lglock: add read-preference local-global rwlock In-Reply-To: <51361540.3060603@cn.fujitsu.com> References: <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> <20130302170656.GB29769@redhat.com> <51361540.3060603@cn.fujitsu.com> Message-ID: <20130305163522.GA4179@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 03/05, Lai Jiangshan wrote: > > On 03/03/13 01:06, Oleg Nesterov wrote: > > On 03/02, Michel Lespinasse wrote: > >> > >> My version would be slower if it needs to take the > >> slow path in a reentrant way, but I'm not sure it matters either :) > > > > I'd say, this doesn't matter at all, simply because this can only happen > > if we race with the active writer. > > It can also happen when interrupted. (still very rarely) > > arch_spin_trylock() > ------->interrupted, > __this_cpu_read() returns 0. > arch_spin_trylock() fails > slowpath, any nested will be slowpath too. > ... > ..._read_unlock() > <-------interrupt > __this_cpu_inc() > .... Yes sure. Or it can take the local lock after we already take the global fallback_lock. But the same can happen with FALLBACK_BASE, just because we need to take a lock (local or global) first, then increment the counter. > (I worries to much. I tend to remove FALLBACK_BASE now, we should > add it only after we proved we needed it, this part is not proved) Agreed, great ;) Oleg.