linux-kernel - Re: [kvm-devel] [PATCH 4/4] Modify KVM to update guest time accounting.

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Date:	Mon, 20 Aug 2007 17:08:23 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Laurent Vivier <Laurent.Vivier@...l.net>
CC:	Ingo Molnar <mingo@...e.hu>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [kvm-devel] [PATCH 4/4] Modify KVM to update guest time accounting.

Laurent Vivier wrote:
> Avi Kivity wrote:
>   
>> Laurent Vivier wrote:
>>     
>>> [PATCH 4/4] Modify KVM to update guest time accounting.
>>>
>>>   
>>>       
>>> Index: kvm/drivers/kvm/kvm.h
>>> ===================================================================
>>> --- kvm.orig/drivers/kvm/kvm.h    2007-08-20 13:23:53.000000000 +0200
>>> +++ kvm/drivers/kvm/kvm.h    2007-08-20 13:23:58.000000000 +0200
>>> @@ -589,6 +589,17 @@ void kvm_mmu_unload(struct kvm_vcpu *vcp
>>>  
>>>  int kvm_hypercall(struct kvm_vcpu *vcpu, struct kvm_run *run);
>>>  
>>> +static inline void kvm_guest_enter(void)
>>> +{
>>> +#ifdef CONFIG_GUEST_ACCOUNTING
>>> +    current->flags |= PF_VCPU;
>>> +#endif
>>>   
>>>       
>> Since you select GUEST_ACCOUNTING, the #ifdef is always true?
>>     
>
> It is just to avoid error if we compile kvm module outside of the kernel, with
> kernel without support of guest accounting. Can be removed if you want.
>
>   

Ah okay.  We take care of the external module in 
external-module-compat.h (in this case, we can #define PF_VCPU to 0 if 
it is undefined).

>>> +}
>>> +
>>> +static inline void kvm_guest_exit(void)
>>> +{
>>>   
>>>       
>> Missing content?
>>     
>
> No, empty function.
>
> It is just to introduce "symmetry" in code, the VCPU code begins with
> "kvm_guest_start()" and ends with "kvm_guest_exit()". And we have no operation
> to do in kvm_guest_exit() (the PF_VCPU is cleared by account_system_time()), so
> "empty function", removed by the optimizer (I hope).
>   

But what if account_system_time() is not called (because we exited 
before the timer interrupt hit)?


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

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