Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753110AbcL2Qpm (ORCPT ); Thu, 29 Dec 2016 11:45:42 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:43476 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752839AbcL2Qpl (ORCPT ); Thu, 29 Dec 2016 11:45:41 -0500 Date: Thu, 29 Dec 2016 17:42:48 +0100 (CET) From: Thomas Gleixner To: Frederic Weisbecker cc: LKML , Peter Zijlstra , James Hartsock , Ingo Molnar , Rik van Riel Subject: Re: [PATCH] nohz: Fix collision between tick and other hrtimers In-Reply-To: <1482596100-16494-1-git-send-email-fweisbec@gmail.com> Message-ID: References: <1482596100-16494-1-git-send-email-fweisbec@gmail.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1434 Lines: 45 On Sat, 24 Dec 2016, Frederic Weisbecker wrote: > static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > ktime_t now, int cpu) > { > - struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); > u64 basemono, next_tick, next_tmr, next_rcu, delta, expires; > unsigned long seq, basejiff; > ktime_t tick; > @@ -767,7 +766,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > tick.tv64 = expires; > > /* Skip reprogram of event if its not changed */ > - if (ts->tick_stopped && (expires == dev->next_event.tv64)) > + if (ts->tick_stopped && (expires == ts->next_tick.tv64)) > goto out; Good catch! > > /* > @@ -787,6 +786,8 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > trace_tick_stop(1, TICK_DEP_MASK_NONE); > } > > + ts->next_tick = tick; > + > /* > * If the expiration time == KTIME_MAX, then we simply stop > * the tick timer. > @@ -803,7 +804,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > tick_program_event(tick, 1); > out: > /* Update the estimated sleep length */ > - ts->sleep_length = ktime_sub(dev->next_event, now); > + ts->sleep_length = ktime_sub(ts->next_tick, now); This is wrong. If the next event is earlier than the next estimated tick then tick_nohz_get_sleep_length() will return crap and the idle governor will go into a deeper C-state than sensible. Thanks, tglx