From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH v3 4/4] nmi_backtrace: generate one-line reports for idle cpus Date: Tue, 22 Mar 2016 23:28:03 +0100 Message-ID: <1714182.jSNjvC6qiX@vostro.rjw.lan> References: <1458667179-19630-1-git-send-email-cmetcalf@mellanox.com> <1458667179-19630-5-git-send-email-cmetcalf@mellanox.com> <20160322173005.GT6344@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: Received: from v094114.home.net.pl ([79.96.170.134]:60096 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751484AbcCVWZx (ORCPT ); Tue, 22 Mar 2016 18:25:53 -0400 In-Reply-To: <20160322173005.GT6344@twins.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Chris Metcalf , Russell King , Thomas Gleixner , Aaron Tomlin , Ingo Molnar , Andrew Morton , Daniel Thompson , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org On Tuesday, March 22, 2016 06:30:05 PM Peter Zijlstra wrote: > On Tue, Mar 22, 2016 at 01:19:39PM -0400, Chris Metcalf wrote: > > When doing an nmi backtrace of many cores, most of which are idle, > > the output is a little overwhelming and very uninformative. Suppress > > messages for cpus that are idling when they are interrupted and just > > emit one line, "NMI backtrace for N skipped: idling at pc 0xNNN". > > > > We do this by grouping all the cpuidle code together into a new > > .cpuidle.text section, and then checking the address of the > > interrupted PC to see if it lies within that section. > > > > This commit suitably tags x86, arm64, and tile idle routines, > > and only adds in the minimal framework for other architectures. > > > > Acked-by: Peter Zijlstra (Intel) > > Tested-by: Peter Zijlstra (Intel) > > Signed-off-by: Chris Metcalf > > For some reason I found a few CPUs using poll_idle(). > > Rafael, when and why would that ever get selected as a useful idle > state? When the predicted idle time is so short even C1 isn't worth it? Yes, that's the case.