Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754970AbaA1QL2 (ORCPT ); Tue, 28 Jan 2014 11:11:28 -0500 Received: from mail-qc0-f179.google.com ([209.85.216.179]:58074 "EHLO mail-qc0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752937AbaA1QL0 (ORCPT ); Tue, 28 Jan 2014 11:11:26 -0500 MIME-Version: 1.0 In-Reply-To: <20140128132306.GB9172@localhost.localdomain> References: <20140115171704.GB21574@localhost.localdomain> <20140120155145.GB9436@localhost.localdomain> <20140123145842.GD13345@localhost.localdomain> <20140128132306.GB9172@localhost.localdomain> Date: Tue, 28 Jan 2014 08:11:25 -0800 Message-ID: Subject: Re: [QUERY]: Is using CPU hotplug right for isolating CPUs? From: Kevin Hilman To: Frederic Weisbecker Cc: Viresh Kumar , Thomas Gleixner , Peter Zijlstra , Linux Kernel Mailing List , Lists linaro-kernel , Steven Rostedt , Linaro Networking Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 28, 2014 at 5:23 AM, Frederic Weisbecker wrote: > On Fri, Jan 24, 2014 at 10:51:14AM +0530, Viresh Kumar wrote: >> On 23 January 2014 20:28, Frederic Weisbecker wrote: >> > On Tue, Jan 21, 2014 at 04:03:53PM +0530, Viresh Kumar wrote: >> >> >> So, the main problem in my case was caused by this: >> >> >> >> <...>-2147 [001] d..2 302.573881: hrtimer_start: >> >> hrtimer=c172aa50 function=tick_sched_timer expires=602075000000 >> >> softexpires=602075000000 >> >> >> >> I have mentioned this earlier when I sent you attachments. I think >> >> this is somehow >> >> tied with the NO_HZ_FULL stuff? As the timer is queued for 300 seconds after >> >> current time. >> >> >> >> How to get this out? >> > >> > So it's scheduled away 300 seconds later. It might be a pending timer_list. Enabling the >> > timer tracepoints may give you some clues. >> >> Trace was done with that enabled. /proc/timer_list confirms that a hrtimer >> is queued for 300 seconds later for tick_sched_timer. And so I assumed >> this is part of the current NO_HZ_FULL implementation. >> >> Just to confirm, when we decide that a CPU is running a single task and so >> can enter tickless mode, do we queue this tick_sched_timer for 300 seconds >> ahead of time? If not, then who is doing this :) > > No, when a single task is running on a full dynticks CPU, the tick is supposed to run > every seconds. I'm actually suprised it doesn't happen in your traces, did you tweak > something specific? I think Viresh is using my patch/hack to configure/disable the 1Hz residual tick. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/