From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: Does anyone use CONFIG_TINY_PREEMPT_RCU? Date: Mon, 12 Nov 2012 17:32:36 -0800 Message-ID: <20121113013236.GM2518@linux.vnet.ibm.com> References: <20121113004906.GA10557@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, sbw@mit.edu, patches@linaro.org To: Frederic Weisbecker Return-path: Received: from e6.ny.us.ibm.com ([32.97.182.146]:41238 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753851Ab2KMBcp (ORCPT ); Mon, 12 Nov 2012 20:32:45 -0500 Received: from /spool/local by e6.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 12 Nov 2012 20:32:45 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: On Tue, Nov 13, 2012 at 02:12:27AM +0100, Frederic Weisbecker wrote: > 2012/11/13 Paul E. McKenney : > > Hello! > > > > I know of people using TINY_RCU, TREE_RCU, and TREE_PREEMPT_RCU, but I > > have not heard of anyone using TINY_PREEMPT_RCU for whom TREE_PREEMPT_RCU > > was not a viable option (in contrast, the people running Linux on > > tiny-memmory systems typically use TINY_RCU). Of course, if no one > > really needs it, the proper thing to do is to remove it. > > > > So, if you need TINY_PREEMPT_RCU, please let me know. Otherwise, I will > > remove it, probably in the 3.9 timeframe. > > I don't use it personally but if you remove it, does that mean that > RCU couldn't be preemptible on UP? It would mean that a kernel built with SMP=n and PREEMPT=y would use TREE_PREEMPT_RCU rather than the current TINY_PREEMPT_RCU. So it would work just as well, but use somewhat more memory. Thanx, Paul