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 S1750933Ab1ITNHL (ORCPT <rfc822;w@1wt.eu>);
	Tue, 20 Sep 2011 09:07:11 -0400
Received: from mx2.parallels.com ([64.131.90.16]:43702 "EHLO mx2.parallels.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750746Ab1ITNHJ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Tue, 20 Sep 2011 09:07:09 -0400
Message-ID: <4E788FD1.40301@parallels.com>
Date: Tue, 20 Sep 2011 10:06:25 -0300
From: Glauber Costa <glommer@parallels.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2
MIME-Version: 1.0
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: <linux-kernel@vger.kernel.org>, <xemul@parallels.com>,
        <paul@paulmenage.org>, <lizf@cn.fujitsu.com>, <daniel.lezcano@free.fr>,
        <mingo@elte.hu>, <jbottomley@parallels.com>
Subject: Re: [PATCH 8/9] per-cgroup boot time
References: <1316030695-19826-1-git-send-email-glommer@parallels.com>   <1316030695-19826-9-git-send-email-glommer@parallels.com>  <1316510746.11841.18.camel@twins> <4E78890D.1000607@parallels.com> <1316523860.13664.11.camel@twins>
In-Reply-To: <1316523860.13664.11.camel@twins>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
X-Originating-IP: [201.82.134.226]
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 09/20/2011 10:04 AM, Peter Zijlstra wrote:
> On Tue, 2011-09-20 at 09:37 -0300, Glauber Costa wrote:
>
>>>> +	getboottime(&boottime);
>>>> +	ts = timespec_add(boottime, ca->start_time);
>>>> +	jif = ts.tv_sec;
>>>>
>>>>    	for_each_possible_cpu(i) {
>>>>    		cpustat = per_cpu_ptr(ca->cpustat, i);
>>>
>>>
>>> I'm confused, what does it do? You take a boot time timestamp at cgroup
>>> creation, add that to all boot-time readings and print the result. How
>>> does that make sense? Subtracting the start_time, maybe, that would make
>>> the cgroup creation time 0, adding, not so much.
>>
>> Boot time represent at which times the machine was booted. In this
>> context, at which time the container/cgroup was created. So it have to
>> be an addition.... don't really understand your question
>
> I think we're all properly confused now :-)
>
> getboottime() gives a time since boot, right?
>
> You take stamp at cgroup creation: say 50s after boot.
>
> Then on usage you take a new getboottime() reading (which per definition
> is>  50s) and add your 50s that you read previous. This results in the
> cgroup having 50s of boot-time _MORE_ than the machine. Say you read at
> 123s, you then add your 50s timestamp, resulting in 173s to report.
>
> If instead you did a subtraction: 123-50=73, you would have reported the
> time since cgroup creation.
>
no.

/**
  * getboottime - Return the real time of system boot.
  * @ts:         pointer to the timespec to be set
  *
  * Returns the wall-time of boot in a timespec.
...