Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933022AbaDIKtp (ORCPT ); Wed, 9 Apr 2014 06:49:45 -0400 Received: from mail-oa0-f46.google.com ([209.85.219.46]:44390 "EHLO mail-oa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932482AbaDIKto (ORCPT ); Wed, 9 Apr 2014 06:49:44 -0400 MIME-Version: 1.0 In-Reply-To: References: Date: Wed, 9 Apr 2014 16:19:44 +0530 Message-ID: Subject: Re: [Query]: tick-sched: why don't we stop tick when we are running idle task? From: Viresh Kumar To: =?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?= Cc: Thomas Gleixner , Linux Kernel Mailing List , Lists linaro-kernel Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9 April 2014 16:03, Viresh Kumar wrote: > Hi Frederic, > > File: kernel/time/tick-sched.c > Function: tick_nohz_full_stop_tick() > > We are doing this: > > if (!tick_nohz_full_cpu(cpu) || is_idle_task(current)) > return; > > Which means: if a FULL_NO_HZ cpu is running idle task currently, > don't stop its tick.. > > I couldn't understand why. Can you please help here? Is it because of this code ? : void tick_nohz_irq_exit(void) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); if (ts->inidle) __tick_nohz_idle_enter(ts); else tick_nohz_full_stop_tick(ts); } i.e. tick_nohz_full_stop_tick() would never be called while we have 'inidle' set or we are running idle task? In this case as well, we don't really need that check to be present. -- 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/