From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755270AbbCPUYP (ORCPT ); Mon, 16 Mar 2015 16:24:15 -0400 Received: from www.linutronix.de ([62.245.132.108]:37681 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754094AbbCPUYN (ORCPT ); Mon, 16 Mar 2015 16:24:13 -0400 Date: Mon, 16 Mar 2015 21:24:09 +0100 From: Sebastian Andrzej Siewior To: Mike Galbraith Cc: linux-rt-users , LKML , Thomas Gleixner , rostedt@goodmis.org, John Kacur Subject: Re: [rfc patch v2] rt,nohz_full: fix nohz_full for PREEMPT_RT_FULL Message-ID: <20150316202409.GF28130@linutronix.de> References: <20150216111822.GA21649@linutronix.de> <1424258514.3819.39.camel@gmail.com> <20150309134535.GA13768@linutronix.de> <1425911771.30469.8.camel@gmail.com> <1425980136.3507.17.camel@gmail.com> <1426153093.4190.2.camel@gmail.com> <1426222405.17611.7.camel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1426222405.17611.7.camel@gmail.com> X-Key-Id: 2A8CF5D1 X-Key-Fingerprint: 6425 4695 FFF0 AA44 66CC 19E6 7B96 E816 2A8C F5D1 User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mike Galbraith | 2015-03-13 05:53:25 [+0100]: >First of all, a task being ticked and trying to shut the tick down will >fail to do so due to having just awakened ksoftirqd, so let ksoftirqd >try to do that after SOFTIRQ_TIMER processing. Secondly, should the >tick be shut down, we may livelock in hrtimer-cancel() because in -rt >a callback may be running. Break the loop, and let tick_nohz_restart() >know that the timer is busy so it can bail. I am a bit undecided on that one. I included it in the series but did not enable it yet. Just so we are on the same page here: you boot your machine with something like "isolcpus=1-31 rcu_nocbs=1-31 nohz_full=1-31" and pin all kernel threads to CPU0, right? What you do is that you accept the fact that the timer-softirq is scheduled for no reason and then you try to disable the tick from within the timer-softirq. I assumed that it would work get the "expired timer" somehow. >Signed-off-by: Mike Galbraith Sebastian