From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752374AbbEGHud (ORCPT ); Thu, 7 May 2015 03:50:33 -0400 Received: from mail-ob0-f171.google.com ([209.85.214.171]:32830 "EHLO mail-ob0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752026AbbEGHub (ORCPT ); Thu, 7 May 2015 03:50:31 -0400 MIME-Version: 1.0 In-Reply-To: References: Date: Thu, 7 May 2015 13:20:30 +0530 Message-ID: Subject: Re: [PATCH V2 0/2] clockevents: Stop unused clockevent devices From: Viresh Kumar To: Thomas Gleixner , Ingo Molnar , Peter Zijlstra Cc: Linaro Kernel Mailman List , Linux Kernel Mailing List , Frederic Weisbecker , Kevin Hilman , Daniel Lezcano , Preeti U Murthy , Viresh Kumar Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3 April 2015 at 09:04, Viresh Kumar wrote: > Hi, > > A clockevent device is used to service timers/hrtimers requests and the next > event (when it should fire) is decided by the timer/hrtimer expiring next. When > no timers/hrtimers are pending to be serviced, the expiry time is set to a > special value: KTIME_MAX. > > This would normally happen with NO_HZ_{IDLE|FULL} in both LOWRES/HIGHRES modes. > > When 'expiry == KTIME_MAX', we either cancel the 'tick-sched' hrtimer > (NOHZ_MODE_HIGHRES) or skip reprogramming clockevent device (NOHZ_MODE_LOWRES). > But, the clockevent device is already reprogrammed from the tick-handler for > next tick. > > As the clock event device is programmed in ONESHOT mode it will at least fire > one more time (unnecessarily). Timers on few implementations (like > arm_arch_timer, etc.) only support PERIODIC mode and their drivers emulate > ONESHOT over that. Which means that on these platforms we will get spurious > interrupts periodically (at last programmed interval rate, normally tick rate). > > In order to avoid spurious interrupts, the unused clockevent device should be > stopped or its interrupts should be masked. > > Thomas suggested to add an optional state ONESHOT_STOPPED to solve this problem: > lkml.org/lkml/2014/5/9/508. > > First patch implements the required infrastructure to start/stop clockevent > device. The second patch stops/starts clockevent devices as and when required. > > It is also pushed here: > > git://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git tick/oneshot-stopped > > @Preeti: I have applied your Reviewed-by only for the first commit as others > have changed significantly. Feel free to give it again :) > > V1->V2: > - Peter & Ingo suggested to to start/stop clockevent device from > tick_program_event() instead of the call sites that called > tick_program_event(). Hi Thomas, Gentle reminder ping... -- viresh