linux-kernel - Re: [PATCH 2/3] kvmclock

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Message-ID: <4739B85B.2080102@qumranet.com>
Date:	Tue, 13 Nov 2007 16:44:43 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Glauber de Oliveira Costa <gcosta@...hat.com>
CC:	linux-kernel@...r.kernel.org, jeremy@...p.org, aliguori@...ibm.com,
	kvm-devel@...ts.sourceforge.net, hollisb@...ibm.com
Subject: Re: [PATCH 2/3] kvmclock - the host part.

Glauber de Oliveira Costa wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Avi Kivity escreveu:
>   
>> Glauber de Oliveira Costa wrote:
>>     
>>> This is the host part of kvm clocksource implementation. As it does
>>> not include clockevents, it is a fairly simple implementation. We
>>> only have to register a per-vcpu area, and start writting to it
>>> periodically.
>>>
>>>   
>>>       
>> Missing live migration support  (a way for userspace to read and write
>> the guest clock address).  Should probably be in a separate patch.
>>     
>
> I think it's a matter of issuing a hypercall for reading the clock
> address. It's fair simple, and can be done in a later version of this patch.
> As for writting, the register hypercall itself can be used. It has no
> special side-effects we should care about.
>   

kvm live migration is done (at least thus far) without guest 
involvement.  So you need the host to be able to transfer this state.


>   
>>> @@ -1924,6 +1955,7 @@ out:
>>>          goto preempted;
>>>      }
>>>  
>>> +    kvm_write_guest_time(vcpu);
>>>      post_kvm_run_save(vcpu, kvm_run);
>>>   
>>>       
>> Why here?  Seems like we're leaving the guest for a while at this place.
>>
>> Suggest putting it on top of __vcpu_run(), guarded by a flag, and
>> setting the flag every time we put the vcpu.
>>     
>
> No special preference. It just sounded exity enough to me. I can move to
> where you suggest.
>
>   

It's more than a place, it's a set of rules:

- if the vcpu is migrated, we need a new timebase
- ditto if we're descheduled (well that's the same thing)
- if "some time passes"


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

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