linux-kernel - Re: [PATCH v2] core, x86: Add user return notifiers

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Message-ID: <4AB89D81.5080808@redhat.com>
Date:	Tue, 22 Sep 2009 12:48:49 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v2] core, x86: Add user return notifiers

On 09/22/2009 12:37 PM, Arjan van de Ven wrote:
> On Tue, 22 Sep 2009 12:25:33 +0300
> Avi Kivity<avi@...hat.com>  wrote:
>
>    
>> On 09/19/2009 09:40 AM, Avi Kivity wrote:
>>      
>>> Add a general per-cpu notifier that is called whenever the kernel is
>>> about to return to userspace.  The notifier uses a thread_info flag
>>> and existing checks, so there is no impact on user return or context
>>> switch fast paths.
>>>
>>>        
>> Ingo/Peter?
>>      
> isn't this like really expensive when used ?
>    

No, why?  It triggers a call to do_notify_resume() and a walks a list of 
length 1.

-- 
error compiling committee.c: too many arguments to function

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