Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933372AbaDIP3x (ORCPT ); Wed, 9 Apr 2014 11:29:53 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.232]:42469 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932908AbaDIP3w (ORCPT ); Wed, 9 Apr 2014 11:29:52 -0400 Date: Wed, 9 Apr 2014 11:29:50 -0400 From: Steven Rostedt To: Viresh Kumar Cc: Thomas Gleixner , "Paul E. McKenney" , Matthew Whitehead , John Stultz , "linux-kernel@vger.kernel.org" , mwhitehe@redhat.com Subject: Re: nohz problem with idle time on old hardware Message-ID: <20140409112950.7be9f8ac@gandalf.local.home> In-Reply-To: References: <20131113113927.GA13875@mwhitehe.csb> <20131113102153.5f10e6b5@gandalf.local.home> <20131113103134.5b8cf02f@gandalf.local.home> <20131113105737.3f7a0b1b@gandalf.local.home> <20131113111257.482c2955@gandalf.local.home> <20131113161829.GE4138@linux.vnet.ibm.com> <20131113112338.7d303c0f@gandalf.local.home> <20131113163552.GF4138@linux.vnet.ibm.com> <20140409103138.29be16b9@gandalf.local.home> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.142:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 9 Apr 2014 20:50:59 +0530 Viresh Kumar wrote: > On 9 April 2014 20:01, Steven Rostedt wrote: > > Ouch! You are correct, this part of the patch makes no sense. That's > > what I get for reviewing a patch and not looking at all the code around > > the changes. (another kernel developer hangs head in shame :-( ) > > > > I think that if statement should be nuked. > > Hmm, my opinion differs here :) > > If we completely remove this statement, we will run > tick_nohz_switch_to_nohz() even if nohz is not enabled. And check for > enabled must stay. Do we? This is only called by tick_check_oneshot_change() which has the following: int tick_check_oneshot_change(int allow_nohz) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); if (!test_and_clear_bit(0, &ts->check_clocks)) return 0; if (ts->nohz_mode != NOHZ_MODE_INACTIVE) return 0; if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) return 0; if (!allow_nohz) return 1; tick_nohz_switch_to_nohz(); return 0; } How often does it make it to that last check? -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/