From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754476Ab1I1OBJ (ORCPT ); Wed, 28 Sep 2011 10:01:09 -0400 Received: from mga14.intel.com ([143.182.124.37]:43452 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752039Ab1I1OBI (ORCPT ); Wed, 28 Sep 2011 10:01:08 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.68,455,1312182000"; d="scan'208";a="56567863" Message-ID: <4E8328A2.3070806@linux.intel.com> Date: Wed, 28 Sep 2011 07:01:06 -0700 From: Arjan van de Ven User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:7.0) Gecko/20110922 Thunderbird/7.0 MIME-Version: 1.0 To: Peter Zijlstra CC: Venki Pallipadi , Thomas Gleixner , Ingo Molnar , Suresh Siddha , linux-kernel@vger.kernel.org Subject: Re: [RFC] Introduce greedy hrtimer walk on idle References: <1316804080-6396-1-git-send-email-venki@google.com> <1316808181.9084.49.camel@twins> <1317216203.24040.18.camel@twins> In-Reply-To: <1317216203.24040.18.camel@twins> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/28/2011 6:23 AM, Peter Zijlstra wrote: > On Fri, 2011-09-23 at 16:47 -0700, Venki Pallipadi wrote: >> On Fri, Sep 23, 2011 at 1:03 PM, Peter Zijlstra wrote: >>> On Fri, 2011-09-23 at 11:54 -0700, Venkatesh Pallipadi wrote: >>>> Comments? >>> Looks to be a possible IRQ latency issue as well, that can be a lot of >>> timers to run.. >>> >> We could add some rate limit on how many timers we service this way >> and/or interrupt/disable-enable in the inner loop. >> But, this would be a problem with current hrtimer as well. When >> sched_tick timer is not around, we may end up servicing lot of timers >> depending on number of them and slack. No? > Right, still something to consider. We might just have to push down on > slack for -rt or so when it becomes a problem. that might not be the right answer ;-) Slack gives you freedom to schedule these guys; without slack you can still get bursts of timers, but with no freedom to punt some for RT behavior. with slack, you can run the mandatory ones first, and then the optionals until you hit some RT limit.. the optionals you do run are not going to bunch up to you at the time they become mandatory.