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Subject: Re: [PATCH] xen: add steal_clock support on x86
To: Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
References: <1463573758-11441-1-git-send-email-jgross@suse.com>
 <573C804F.6020708@oracle.com> <573C81D1.9040309@suse.com>
Cc: sstabellini@kernel.org, david.vrabel@citrix.com
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <573C896F.4090303@oracle.com>
Date: Wed, 18 May 2016 11:25:35 -0400
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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
>