From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757704AbdJQAHu (ORCPT ); Mon, 16 Oct 2017 20:07:50 -0400 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:42497 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752490AbdJQAHt (ORCPT ); Mon, 16 Oct 2017 20:07:49 -0400 From: "Rafael J. Wysocki" To: "Li, Aubrey" Cc: Aubrey Li , tglx@linutronix.de, peterz@infradead.org, len.brown@intel.com, ak@linux.intel.com, tim.c.chen@linux.intel.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 5/8] timers: keep sleep length updated as needed Date: Tue, 17 Oct 2017 01:58:13 +0200 Message-ID: <35931824.svOhBhJZiB@aspire.rjw.lan> In-Reply-To: <33404efd-a8e0-eb0b-4df8-9e7aa5a66dde@linux.intel.com> References: <1506756034-6340-1-git-send-email-aubrey.li@intel.com> <1554921.dz8jk4n8cL@aspire.rjw.lan> <33404efd-a8e0-eb0b-4df8-9e7aa5a66dde@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday, October 16, 2017 8:46:41 AM CEST Li, Aubrey wrote: > On 2017/10/14 8:56, Rafael J. Wysocki wrote: > > On Saturday, September 30, 2017 9:20:31 AM CEST Aubrey Li wrote: > >> sleep length indicates how long we'll be idle. Currently, it's updated > >> only when tick nohz enters. These patch series make a new requirement > >> with tick, so we should keep sleep length updated as needed > > > > So what exactly would be the problem with leaving things as they are? > > Previously ts->sleep_length is only updated when tick is stopped. > > As follows, in > > __tick_nohz_idle_enter() > { > if (can_stop_idle_tick() /* return true */) { > tick_nohz_stop_sched_tick() > | > |-----> update sleep_length > } > } Which is logical, because the tick will get in the way if we don't stop it, won't it? > > Now ts->sleep_length is required out of tick_nohz_idle_enter(), so we want > to update sleep_length every time we read it > > If we leave it unchanged, the prediction could read a sleep_length long time > ago if the system keep ticking. Well, but does it make sense to estimate the sleep length without stopping the tick? > >> --- > >> kernel/time/tick-sched.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > >> index d663fab..94fb9b8 100644 > >> --- a/kernel/time/tick-sched.c > >> +++ b/kernel/time/tick-sched.c > >> @@ -1008,8 +1008,11 @@ void tick_nohz_irq_exit(void) > >> */ > >> ktime_t tick_nohz_get_sleep_length(void) > >> { > >> + struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); > >> struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); > >> > >> + ts->sleep_length = ktime_sub(dev->next_event, ktime_get()); > >> + > >> return ts->sleep_length; > >> } > >> > >> > > > > I probably wouldn't do it this way ... > > > > > > May I know the detailed thoughts? That depends on the answer above. :-) Thanks, Rafael