From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754419Ab3AGRHE (ORCPT ); Mon, 7 Jan 2013 12:07:04 -0500 Received: from e37.co.us.ibm.com ([32.97.110.158]:40072 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750913Ab3AGRHB (ORCPT ); Mon, 7 Jan 2013 12:07:01 -0500 Date: Mon, 7 Jan 2013 08:57:48 -0800 From: "Paul E. McKenney" To: Josh Triplett Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, 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, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org Subject: Re: [PATCH tip/core/rcu 1/1] Tiny RCU changes for 3.9 Message-ID: <20130107165748.GF2525@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20130105175059.GA15961@linux.vnet.ibm.com> <20130107155810.GC11145@leaf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130107155810.GC11145@leaf> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13010717-7408-0000-0000-00000B9FE751 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 07, 2013 at 07:58:10AM -0800, Josh Triplett wrote: > On Sat, Jan 05, 2013 at 09:50:59AM -0800, Paul E. McKenney wrote: > > rcu: Provide RCU CPU stall warnings for tiny RCU > > > > Tiny RCU has historically omitted RCU CPU stall warnings in order to > > reduce memory requirements, however, lack of these warnings caused Thomas > > Gleixner some debugging pain recently. Therefore, this commit adds RCU > > CPU stall warnings to tiny RCU if RCU_TRACE=y. This keeps the memory > > footprint small, while still enabling CPU stall warnings in kernels > > built to enable them. > > > > This is still a bit on the high-risk side, so running this will likely > > be a debugging exercise. > > > > Reported-by: Thomas Gleixner > > Signed-off-by: Paul E. McKenney > > Signed-off-by: Paul E. McKenney > > Did you generate this patch with something other than git? The > formatting seems a bit off: it doesn't have a diffstat or the usual > "---" line between the commit message and the patch. Indeed I did -- couldn't see the point of sending a 0/1 and 1/1 series of patches. ;-) > This patch seems reasonable to me, but the repeated use of #if > defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE) seems somewhat > annoying, and fragile if you ever decide to change the conditions. How > about defining an appropriate symbol in Kconfig for stall warnings, and > using that? But I only just removed the config option for SMP RCU stall warnings. ;-) But I must agree that "defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE)" is a bit obscure. The rationale is that RCU stall warnings are unconditionally enabled in SMP kernels, but don't want to be in TINY_RCU kernels due to size constraints. I therefore put it under CONFIG_RCU_TRACE, which also contains other TINY_RCU debugging-style options. Would adding a comment to this effect help? Thanx, Paul