From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S934161AbbDIJLq (ORCPT <rfc822;w@1wt.eu>);
	Thu, 9 Apr 2015 05:11:46 -0400
Received: from www.linutronix.de ([62.245.132.108]:45825 "EHLO
	Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754976AbbDII6A (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 9 Apr 2015 04:58:00 -0400
Date: Thu, 9 Apr 2015 10:58:16 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Ingo Molnar <mingo@kernel.org>
cc: Peter Zijlstra <peterz@infradead.org>,
        Viresh Kumar <viresh.kumar@linaro.org>, Ingo Molnar <mingo@redhat.com>,
        linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>
Subject: Re: [PATCH] hrtimer: Replace cpu_base->active_bases with a direct
 check of the active list
In-Reply-To: <20150409072038.GA30205@gmail.com>
Message-ID: <alpine.DEB.2.11.1504091054410.3845@nanos>
References: <cover.1428039899.git.viresh.kumar@linaro.org> <b884675ccbd86069d7e9ff6b0de35760c5d6a959.1428039899.git.viresh.kumar@linaro.org> <alpine.DEB.2.11.1504082019220.3845@nanos> <20150409062841.GB14259@gmail.com> <20150409065730.GK27490@worktop.programming.kicks-ass.net>
 <20150409070917.GF14259@gmail.com> <20150409072038.GA30205@gmail.com>
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

On Thu, 9 Apr 2015, Ingo Molnar wrote:
> Plus, look at this code in hrtimer_run_queues():
> 
>         for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
>                 base = &cpu_base->clock_base[index];
>                 if (!base->active.next)
>                         continue;
> 
>                 if (gettime) {
>                         hrtimer_get_softirq_time(cpu_base);
>                         gettime = 0;
>                 }
> 
> if at least one base is active (on my fairly standard system all cpus 
> have at least one active hrtimer base all the time - and many cpus 
> have two bases active), then we run hrtimer_get_softirq_time(), which 
> dirties the cachelines of all 4 clock bases:
> 
>         base->clock_base[HRTIMER_BASE_REALTIME].softirq_time = xtim;
>         base->clock_base[HRTIMER_BASE_MONOTONIC].softirq_time = mono;
>         base->clock_base[HRTIMER_BASE_BOOTTIME].softirq_time = boot;
>         base->clock_base[HRTIMER_BASE_TAI].softirq_time = tai;

This is the non highres case and we actually could optimize that case
as well to avoid the cache line polution.

Thanks,

	tglx