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Date: Wed, 23 Feb 2011 17:15:31 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] Re: Strategic decision: COW format
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Chunqiang Tang <ctang@us.ibm.com>, Markus Armbruster <armbru@redhat.com>, Avi Kivity <avi@redhat.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, qemu-devel@nongnu.org

Am 23.02.2011 17:04, schrieb Anthony Liguori:
> On 02/23/2011 10:03 AM, Avi Kivity wrote:
>> On 02/23/2011 05:50 PM, Anthony Liguori wrote:
>>>> I still don't see.  What would you do with thousands of checkpoints?
>>>
>>>
>>> For reverse debugging, if you store checkpoints at a rate of save, 
>>> every 10ms, and then degrade to storing every 100ms after 1 second, 
>>> etc. you'll have quite a large number of snapshots pretty quickly.  
>>> The idea of snapshotting with reverse debugging is that instead of 
>>> undoing every instruction, you can revert to the snapshot before, and 
>>> then replay the instruction stream until you get to the desired point 
>>> in time.
>>
>> You cannot replay the instruction stream since inputs (interrupts, 
>> rdtsc or other timers, I/O) will be different.  You need Kemari for this.
> 
> Yes, I'm well aware of this.  I don't think all the pieces where ever 
> really there to do this.

So why exactly was this a requirement for internal snapshots to be
consider usable in a reasonable way? ;-)

Anyway, I actually think with internal snapshots you're better suited to
implement something like this than with external snapshots.

Kevin