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 S932799AbcHIXfd (ORCPT <rfc822;w@1wt.eu>);
	Tue, 9 Aug 2016 19:35:33 -0400
Received: from mail-wm0-f66.google.com ([74.125.82.66]:33857 "EHLO
	mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932593AbcHIXfb (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 9 Aug 2016 19:35:31 -0400
MIME-Version: 1.0
In-Reply-To: <CANRm+CzxWo9i_=Ygn4CAF0L5=1avtnX=ahwMK96fj3hnQW-_zA@mail.gmail.com>
References: <1468421405-20056-1-git-send-email-fweisbec@gmail.com>
 <1468421405-20056-2-git-send-email-fweisbec@gmail.com> <CANRm+CyYHLaihuk+ckQg42-Lo_3vFHaS8gU=GmXh8Rfq5mMpaA@mail.gmail.com>
 <1470751579.13905.77.camel@redhat.com> <CANRm+CzxWo9i_=Ygn4CAF0L5=1avtnX=ahwMK96fj3hnQW-_zA@mail.gmail.com>
From: Wanpeng Li <kernellwp@gmail.com>
Date: Wed, 10 Aug 2016 07:35:29 +0800
Message-ID: <CANRm+Cwy=JH4i2O_2ZgGkRXybZjB1=VEbKetGYhanonRcC8qzQ@mail.gmail.com>
Subject: Re: [PATCH 1/5] sched,time: Count actually elapsed irq & softirq time
To: Rik van Riel <riel@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Wanpeng Li <wanpeng.li@hotmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Radim Krcmar <rkrcmar@redhat.com>, Mike Galbraith <efault@gmx.de>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

2016-08-10 7:25 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> 2016-08-09 22:06 GMT+08:00 Rik van Riel <riel@redhat.com>:
>> On Tue, 2016-08-09 at 11:59 +0800, Wanpeng Li wrote:
>>> Hi Rik,
>>> 2016-07-13 22:50 GMT+08:00 Frederic Weisbecker <fweisbec@gmail.com>:
>>> > From: Rik van Riel <riel@redhat.com>
>>> >
>>> > Currently, if there was any irq or softirq time during 'ticks'
>>> > jiffies, the entire period will be accounted as irq or softirq
>>> > time.
>>> >
>>> > This is inaccurate if only a subset of the time was actually spent
>>> > handling irqs, and could conceivably mis-count all of the ticks
>>> > during
>>> > a period as irq time, when there was some irq and some softirq
>>> > time.
>>> >
>>> > This can actually happen when irqtime_account_process_tick is
>>> > called
>>> > from account_idle_ticks, which can pass a larger number of ticks
>>> > down
>>> > all at once.
>>> >
>>> > Fix this by changing irqtime_account_hi_update,
>>> > irqtime_account_si_update,
>>> > and steal_account_process_ticks to work with cputime_t time units,
>>> > and
>>> > return the amount of time spent in each mode.
>>>
>>> Do we need to minus st cputime from idle cputime in
>>> account_idle_ticks() when noirqtime is true? I try to add this logic
>>> w/ noirqtime and idle=poll boot parameter for a full dynticks guest,
>>> however, there is no difference, where I miss?
>>
>> Yes, you are right. The code in account_idle_ticks()
>> could use the same treatment.
>>
>> I am not sure why it would not work, though...
>
> Actually I observed a regression caused by this patch. I use a i5

The regression is caused by your commit "sched,time: Count actually
elapsed irq & softirq time".

> laptop, 4 pCPUs, 4vCPUs for one full dynticks guest, there are four
> cpu hog processes(for loop) running in the guest, I hot-unplug the
> pCPUs on host one by one until there is only one left, then observe
> the top in guest, there are 100% st for cpu0(housekeeping), and 75% st
> for other cpus(nohz full). However, w/o this patch, 75% for all the
> four cpus.
>
> I try to figure out this recently, any tip is a great appreciated. :)
>
> Regards,
> Wapeng Li