linux-kernel - Re: [BUG] Paravirtual time accounting / IRQ time accounting

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Date:	Sat, 22 Mar 2014 10:57:28 -0400
From:	Rik van Riel <riel@...hat.com>
To:	lwcheng@...hku.hk
CC:	Glauber Costa <glommer@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] Paravirtual time accounting / IRQ time accounting

On 03/22/2014 03:15 AM, lwcheng@...hku.hk wrote:

> I observe that sometimes irq_time only includes "part" of steal_time.
> 
> Like you said, irq_time is in dozens-of-microseconds. In VMs, as all
> devices seen are virtual ones, irq_time seems to be not as desired
> as it is in physical hosts.
> 
> A quick (but not radical) solution may be:
> disable CONFIG_IRQ_TIME_ACCOUNTING if CONFIG_PARAVIRT is selected.
> Just adopt tick-based accounting: CONFIG_TICK_CPU_ACCOUNTING
> 
> I am thinking what irq_time really *means* in VMs.

That is not really an option for Linux distributions, which tend
to run the same kernel image on the host and in the guest...

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