From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754214Ab3AGR4R (ORCPT ); Mon, 7 Jan 2013 12:56:17 -0500 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:54767 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751337Ab3AGR4Q (ORCPT ); Mon, 7 Jan 2013 12:56:16 -0500 X-Originating-IP: 217.70.178.140 X-Originating-IP: 173.246.103.110 Date: Mon, 7 Jan 2013 09:56:06 -0800 From: Josh Triplett To: "Paul E. McKenney" 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: <20130107175606.GA9962@jtriplet-mobl1> References: <20130105175059.GA15961@linux.vnet.ibm.com> <20130107155810.GC11145@leaf> <20130107165748.GF2525@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130107165748.GF2525@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 07, 2013 at 08:57:48AM -0800, Paul E. McKenney wrote: > 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. ;-) Just don't pass --cover-letter to git format-patch and you won't get the 0/1. > > 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? I understand the rationale; I just think it would become clearer if you added an internal-only Kconfig symbol selected in both cases and change the conditionals to use that. - Josh Triplett