Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751696AbbKPPHs (ORCPT <rfc822;w@1wt.eu>);
	Mon, 16 Nov 2015 10:07:48 -0500
Received: from www.linutronix.de ([62.245.132.108]:41087 "EHLO
	Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750781AbbKPPHq (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 16 Nov 2015 10:07:46 -0500
Date: Mon, 16 Nov 2015 16:06:57 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Len Brown <len.brown@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Eduardo Valentin <edubezval@gmail.com>, Paul Turner <pjt@google.com>
Subject: Re: [PATCH 2/4] timer: relax tick stop in idle entry
In-Reply-To: <20151113142438.3144d47d@icelake>
Message-ID: <alpine.DEB.2.11.1511161558550.3761@nanos>
References: <1447444387-23525-1-git-send-email-jacob.jun.pan@linux.intel.com> <1447444387-23525-3-git-send-email-jacob.jun.pan@linux.intel.com> <alpine.DEB.2.11.1511131516180.3987@nanos> <20151113142438.3144d47d@icelake>
User-Agent: Alpine 2.11 (DEB 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1529
Lines: 34

On Fri, 13 Nov 2015, Jacob Pan wrote:
>           <idle>-0     [000]    30.093473: bprint:               __tick_nohz_idle_enter: JPAN: __tick_nohz_idle_enter 803
>           <idle>-0     [000]    30.093473: bprint:               __tick_nohz_idle_enter: JPAN: can_stop_idle_tick 743
> [JP] can_stop_idle_tick() checks ok to stop tick
> 
>           <idle>-0     [000]    30.093474: bprint:               __tick_nohz_idle_enter: JPAN: tick_nohz_stop_sched_tick 609 delta 1000000
> [JP] but sees delta is exactly 1 tick away. didn't stop tick.

If the delta is 1 tick then it is not supposed to stop it. Did you
ever try to figure out WHY it is 1 tick?

There are two code pathes which can set it to basemono + TICK_NSEC:

        if (rcu_needs_cpu(basemono, &next_rcu) ||
            arch_needs_cpu() || irq_work_needs_cpu()) {
                next_tick = basemono + TICK_NSEC;
        } else {
                next_tmr = get_next_timer_interrupt(basejiff, basemono);
                ts->next_timer = next_tmr;
                /* Take the next rcu event into account */
                next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
        }

Can you please figure out WHY the tick is requested to continue
instead of blindly wreckaging the logic in that code?

Thanks,

	tglx
--
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/