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

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Message-ID: <47398A68.8080009@redhat.com>
Date:	Tue, 13 Nov 2007 09:28:40 -0200
From:	Glauber de Oliveira Costa <gcosta@...hat.com>
To:	Avi Kivity <avi@...ranet.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.

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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.

>> @@ -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.

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