linux-kernel - Re: [PATCH] xen: add steal

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Date:	Wed, 18 May 2016 11:25:35 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
	linux-kernel@...r.kernel.org
Cc:	sstabellini@...nel.org, david.vrabel@...rix.com
Subject: Re: [PATCH] xen: add steal_clock support on x86

On 05/18/2016 10:53 AM, Juergen Gross wrote:
> On 18/05/16 16:46, Boris Ostrovsky wrote:
>> On 05/18/2016 08:15 AM, Juergen Gross wrote:
>>>  }
>>>  
>>> +void __init xen_time_setup_guest(void)
>>> +{
>>> +	pv_time_ops.steal_clock = xen_steal_clock;
>>> +
>>> +	static_key_slow_inc(&paravirt_steal_enabled);
>>> +	/*
>>> +	 * We can't set paravirt_steal_rq_enabled as this would require the
>>> +	 * capability to read another cpu's runstate info.
>>> +	 */
>>> +}
>> Won't we be accounting for stolen cycles twice now --- once from
>> steal_account_process_tick()->steal_clock() and second time from
>> do_stolen_accounting()?
> Uuh, yes.
>
> I guess I should rip do_stolen_accounting() out, too? 

I don't think PARAVIRT_TIME_ACCOUNTING is always selected for Xen. If
that's indeed the case then we should ifndef do_stolen_accounting(). Or
maybe check for paravirt_steal_enabled.

-boris

> It is a
> Xen-specific hack, so I guess nobody will cry. Maybe it would be a
> good idea to select CONFIG_PARAVIRT_TIME_ACCOUNTING for XEN then?
>
>
> Juergen
>