Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262858AbVCWH5T (ORCPT ); Wed, 23 Mar 2005 02:57:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261206AbVCWH5I (ORCPT ); Wed, 23 Mar 2005 02:57:08 -0500 Received: from ms-smtp-03.nyroc.rr.com ([24.24.2.57]:49096 "EHLO ms-smtp-03.nyroc.rr.com") by vger.kernel.org with ESMTP id S262843AbVCWHzB (ORCPT ); Wed, 23 Mar 2005 02:55:01 -0500 Date: Wed, 23 Mar 2005 02:54:53 -0500 (EST) From: Steven Rostedt X-X-Sender: rostedt@localhost.localdomain Reply-To: rostedt@goodmis.org To: Ingo Molnar cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, Esben Nielsen Subject: Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.41-07 In-Reply-To: <20050323071604.GA32712@elte.hu> Message-ID: References: <20050321090122.GA8066@elte.hu> <20050321090622.GA8430@elte.hu> <20050322054345.GB1296@us.ibm.com> <20050322072413.GA6149@elte.hu> <20050322092331.GA21465@elte.hu> <20050322093201.GA21945@elte.hu> <20050322100153.GA23143@elte.hu> <20050322112856.GA25129@elte.hu> <20050323061601.GE1294@us.ibm.com> <20050323063317.GB31626@elte.hu> <20050323071604.GA32712@elte.hu> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1333 Lines: 36 On Wed, 23 Mar 2005, Ingo Molnar wrote: > > * Ingo Molnar wrote: > > > That callback will be queued on CPU#2 - while the task still keeps > > current->rcu_data of CPU#1. It also means that CPU#2's read counter > > did _not_ get increased - and a too short grace period may occur. > > > > it seems to me that that only safe method is to pick an 'RCU CPU' when > > first entering the read section, and then sticking to it, no matter > > where the task gets migrated to. Or to 'migrate' the +1 read count > > from one CPU to the other, within the scheduler. > > i think the 'migrate read-count' method is not adequate either, because > all callbacks queued within an RCU read section must be called after the > lock has been dropped - while with the migration method CPU#1 would be > free to process callbacks queued in the RCU read section still active on > CPU#2. > Hi Ingo, Although you can't disable preemption for the duration of the rcu_readlock, what about pinning the process to a CPU while it has the lock. Would this help solve the migration issue? -- Steve - 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/