Message-ID: <47135D1B.1060004@bull.net>
Date: Mon, 15 Oct 2007 14:29:15 +0200
From: Laurent Vivier <Laurent.Vivier@bull.net>
Organization: Bull S.A.S.
User-Agent: Thunderbird 1.5.0.2 (X11/20060420)
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To: Avi Kivity <avi@qumranet.com>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RESEND 2][PATCH 4/4] Modify KVM to update guest time	accounting.
References: <46E550EF.5080209@bull.net> <20071015093800.GA22818@elte.hu> <47133732.2090809@qumranet.com> <20071015095125.GB28367@elte.hu> <47133ABD.8050608@qumranet.com> <471346B0.8050102@bull.net> <47134BCE.1080306@qumranet.com> <4713510D.2050208@bull.net> <471357E4.90904@qumranet.com>
In-Reply-To: <471357E4.90904@qumranet.com>
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Avi Kivity wrote:
> Laurent Vivier wrote:
>=20
> =20
>=20
>>> But if we didn't get an interrupt in that time?
>>>
>>> We can clear it a bit later, after local_irq_enable() in
>>> __vcpu_run(). However we need a nop instruction first because "sti"
>>> keeps interrupts
>>> disabled for one more instruction.
>>>    =20
>>
>> IMHO, I think it is better to let kvm_guest_exit() empty (you can
>> remove it, if
>> you want):
>>
>> 1st case:
>> - unset PF_VCPU in kvm_guest_exit(), all the tick is always for system=

>> time.
>> Guest time is always 0.
>>
>> 1st case and half:
>>
>> - like 1st case but we move kvm_guest_exit() as you propose and the
>> reason of
>> the interrupt is the tick interrupt. The tick is for guest time only.
>> I think
>> the probability is very low.
>>  =20
>=20
> If the guest is executing for 10% of the time, the probability is
> exactly 10%, no?

I think you know that better than me.

But is there homogeneity in probability ?

I mean, if the guest has a lot I/O, it is interrupted by them and the
probability to be interrupted by a tick is lower than the time passed in =
the VCPU ?

>> 2nd case:
>> - don't unset PF_VCPU in kvm_guest_exit(), all the tick is for guest
>> time.
>>  =20
>=20
> But then even execution in ->handle_exit() is accounted as guest time,
> which is wrong.

System time and User time are wrong too as the tick is accounted to the s=
ide
where it appears, even if CPU has executed code from the other side in a
sub-part of the tick. It's not a good argument.

Laurent
--=20
---------------- Laurent.Vivier@bull.net  -----------------
"Given enough eyeballs, all bugs are shallow" E. S. Raymond


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