Re: [Qemu-devel] [RFC][PATCH 10/16 v6] run dump at the background

[Jan Kiszka]

On 2012-02-15 10:35, Wen Congyang wrote:
> At 02/15/2012 05:21 PM, Jan Kiszka Wrote:
>> On 2012-02-15 10:22, Wen Congyang wrote:
>>> At 02/15/2012 05:07 PM, Jan Kiszka Wrote:
>>>> On 2012-02-15 04:47, Wen Congyang wrote:
>>>>> At 02/15/2012 02:27 AM, Jan Kiszka Wrote:
>>>>>> On 2012-02-14 19:05, Jan Kiszka wrote:
>>>>>>> On 2012-02-09 04:28, Wen Congyang wrote:
>>>>>>>> The new monitor command dump may take long time to finish. So we need 
>>>>>>>> run it
>>>>>>>> at the background.
>>>>>>>
>>>>>>> How does it work? Like live migration, i.e. you retransmit (overwrite)
>>>>>>> already written but then dirtied pages? Hmm... no.
>>>>>>>
>>>>>>> What does background mean then? What is the use case? What if the user
>>>>>>> decides to resume the vm?
>>>>>>
>>>>>> OK, that is addressed in patch 15! I would suggest merging it into this
>>>>>> patch. It makes sense to handle that case gracefully right from the
>>>>>> beginning.
>>>>>
>>>>> OK, I will merge it.
>>>>>
>>>>>>
>>>>>> OK, now I have some other question: What is the point of rate-limiting
>>>>>> the dump? The guest is not running, thus not competing for bandwidth.
>>>>>
>>>>> I use bandwidth to try to control the writing speed. If we write the 
>>>>> vmcore
>>>>> to disk in a high speed, it may affect some other appilications which use
>>>>> the same disk too.
>>>>
>>>> Just like the guest of that particular VM can do. I don't think we need
>>>> this level of control here, it will be provided (if required) at a
>>>> different level, affecting the whole QEMU process. Removing the vmcore
>>>> bandwidth control will simplify code and user interface.
>>>
>>> OK. I will implementing it like this:
>>> 1. write 100ms
>>> 2. sleep 100ms(allow qemu to do the other things)
>>> 3. goto 1
>>
>> Why? Just write as fast as possible.
> 
> If the memory is too big, the command will take too long time. 
> Eric said:
>   It sounds like it is long-running, which
>   means it probably needs to be asynchronous, as well as issue an event
>   upon completion, so that other monitor commands can be issued in the
>   meantime.

Asynchronous doesn't mean throttled. It means not waiting for
potentially long-running I/O in the context of the monitor, but becoming
interactive again.

Jan

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