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 S1754646AbbKJRPI (ORCPT <rfc822;w@1wt.eu>);
	Tue, 10 Nov 2015 12:15:08 -0500
Received: from mga02.intel.com ([134.134.136.20]:7195 "EHLO mga02.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752711AbbKJRPG (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Tue, 10 Nov 2015 12:15:06 -0500
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.20,271,1444719600"; 
   d="scan'208";a="847130526"
Date: Tue, 10 Nov 2015 09:14:08 -0800
From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Len Brown <len.brown@intel.com>, Andi Kleen <andi.kleen@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>, Paul Turner <pjt@google.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Eduardo Valentin <edubezval@gmail.com>,
        Punit Agrawal <punit.agrawal@arm.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection
Message-ID: <20151110091408.5e31366c@icelake>
In-Reply-To: <20151110170010.GH17308@twins.programming.kicks-ass.net>
References: <1447114883-23851-1-git-send-email-jacob.jun.pan@linux.intel.com>
	<1447114883-23851-4-git-send-email-jacob.jun.pan@linux.intel.com>
	<20151110132324.GC17308@twins.programming.kicks-ass.net>
	<20151110060116.26cd5ff8@yairi>
	<20151110145823.GD17308@twins.programming.kicks-ass.net>
	<20151110082859.1493f106@icelake>
	<20151110163646.GG17308@twins.programming.kicks-ass.net>
	<20151110085055.67bdb1fa@icelake>
	<20151110170010.GH17308@twins.programming.kicks-ass.net>
Organization: OTC
X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.23; x86_64-pc-linux-gnu)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, 10 Nov 2015 18:00:10 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> > Different per CPU timer may intercept parameter changes at slightly
> > different time, so there is a race condition such that some CPUs may
> > catch the period change later by one period, which results in a
> > correct period change but at a different time, i.e. out of sync.  
> 
> Ah yes. So if the locking hurts I can come up with a lockless
> algorithm for this. Shouldn't be too hard.
Great! the current patch was designed to be lockless but a
little awkward. My idea was to have a common start time, then we don't
need to worry about CPUs out of sync, at most they will be off by one
period then catch up.

Thanks,

Jacob