From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752019AbaEGUG6 (ORCPT ); Wed, 7 May 2014 16:06:58 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:56985 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751658AbaEGUG5 (ORCPT ); Wed, 7 May 2014 16:06:57 -0400 Date: Wed, 7 May 2014 13:06:55 -0700 From: Andrew Morton To: Borislav Petkov Cc: LKML , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Mel Gorman , Steven Rostedt , Mike Galbraith , Linus Torvalds , "Srivatsa S. Bhat" Subject: Re: [PATCH] CPU hotplug: Slow down hotplug operations Message-Id: <20140507130655.9f7c46de8cb39726079458fb@linux-foundation.org> In-Reply-To: <1399492661-891-1-git-send-email-bp@alien8.de> References: <1399492661-891-1-git-send-email-bp@alien8.de> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 7 May 2014 21:57:41 +0200 Borislav Petkov wrote: > We have all those eager tester dudes which scratch up a dirty script to > pound on CPU hotplug senselessly and then report bugs they've managed to > trigger. > > Well, first of all, most, if not all, bugs they trigger are CPU hotplug > related anyway. But we know hotplug is full of duct tape and brown > paper bags. So we end up clearly wasting too much time dealing with a > mechanism we know it is b0rked in the first place. > > Oh, and I would understand if that pounding were close to some real > usage patterns but I've yet to receive a justification for toggling > cores on- and offline senselessly. > > In any case, before this gets rewritten properly (I'm being told we > might get lucky after all) let's slow down hotplugging on purpose and > thus make it uninteresting, as a temporary brown paper bag solution > until the real thing gets done. > > This way we'll save us a lot of time and efforts in chasing the wrong > bugs. Well, I only yesterday merged Srivatsa's `CPU hotplug, stop-machine: plug race-window that leads to "IPI-to-offline-CPU"' bugfix. That bug presumably wouldn't have been fixed if this patch was in place.