From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753629AbbDBNr2 (ORCPT ); Thu, 2 Apr 2015 09:47:28 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:45821 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753601AbbDBNrY (ORCPT ); Thu, 2 Apr 2015 09:47:24 -0400 Date: Thu, 2 Apr 2015 15:47:13 +0200 From: Peter Zijlstra To: Viresh Kumar Cc: Thomas Gleixner , Ingo Molnar , linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] hrtimer: update '->active_bases' before calling hrtimer_force_reprogram() Message-ID: <20150402134713.GB23123@twins.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 02, 2015 at 04:21:21PM +0530, Viresh Kumar wrote: > 'active_bases' indicates which clock-base have active timers. While it > is updated (almost) correctly, it is hardly used. Next commit will start > using it to make code more efficient, but before that we need to fix a > problem. > > While removing hrtimers, in __remove_hrtimer(): > - We first remove the hrtimer from the queue. > - Then reprogram clockevent device if required > (hrtimer_force_reprogram()). > - And then finally clear 'active_bases', if no more timers are pending > on the current clock base (from which we are removing the hrtimer). > > hrtimer_force_reprogram() needs to loop over all active clock bases to > find the next expiry event, and while doing so it will use > 'active_bases' (after next commit). And it will find the current base > active, as we haven't cleared it until now, even if current clock base > has no more hrtimers queued. > > To fix this issue, clear active_bases before calling > hrtimer_force_reprogram(). This is a small inefficiency right? Not an actual bug or anything.