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Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue |
Date: |
Thu, 4 May 2017 14:52:44 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 |
On 04/05/2017 14:34, Pavel Dovgalyuk wrote:
>> From: Paolo Bonzini [mailto:address@hidden
>> On 04/05/2017 14:10, Pavel Dovgalyuk wrote:
>>>> From: Paolo Bonzini [mailto:address@hidden
>>>> On 04/05/2017 13:54, Pavel Dovgalyuk wrote:
>>>>>> From: Paolo Bonzini [mailto:address@hidden
>>>>>> On 04/05/2017 13:13, Pavel Dovgalyuk wrote:
>>>>>>>>> This patch does not allows saving/loading vmstate when
>>>>>>>>> replay events queue is not empty. There is no reliable
>>>>>>>>> way to save events queue, because it describes internal
>>>>>>>>> coroutine state. Therefore saving and loading operations
>>>>>>>>> should be deferred to another record/replay step.
>>>>>>>>
>>>>>>>> Can it actually be non-empty after bdrv_drain_all?
>>>>>>>
>>>>>>> drain/flush cannot succeed, because started requests are
>>>>>>> prisoned in the replay events queue.
>>>>>>
>>>>>> But that would apply to loading only. Saving should still be always
>>>>>> possible.
>>>>>
>>>>> We can save it. But it wouldn't load correctly - replay queue will be
>>>>> empty after loading.
>>>>
>>>> When saving you can drain, and then the events queue should be empty.
>>>> Or I am misunderstanding how it works, which is possible too.
>>>
>>> Drain will wait until the queue becomes empty.
>>> Queue is processed only at checkpoints.
>>> Checkpoints are met in iothread (at timers processing and so on).
>>> But iothread is waiting for finishing the drain.
>>
>> What checkpoint can hang the drain during a save?
>
> No one. There are no checkpoins during vmsave and during drain.
> Therefore the queue will never become empty.
Understood. And what checkpoint will you be waiting for during drain,
causing a deadlock?
Paolo
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, (continued)
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Juan Quintela, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Paolo Bonzini, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Pavel Dovgalyuk, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Paolo Bonzini, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Pavel Dovgalyuk, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Paolo Bonzini, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Pavel Dovgalyuk, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Paolo Bonzini, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Pavel Dovgalyuk, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Pavel Dovgalyuk, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Paolo Bonzini, 2017/05/04
- Re: [Qemu-devel] [PATCH v9 06/10] replay: fix save/load vm for non-empty queue, Pavel Dovgalyuk, 2017/05/04
[Qemu-devel] [PATCH v9 07/10] replay: added replay log format description, Pavel Dovgalyuk, 2017/05/04
[Qemu-devel] [PATCH v9 08/10] replay: make safe vmstop at record/replay, Pavel Dovgalyuk, 2017/05/04
[Qemu-devel] [PATCH v9 09/10] replay: save prior value of the host clock, Pavel Dovgalyuk, 2017/05/04
[Qemu-devel] [PATCH v9 10/10] icount: fixed saving/restoring of icount warp timers, Pavel Dovgalyuk, 2017/05/04
Re: [Qemu-devel] [PATCH v9 00/10] replay additions, no-reply, 2017/05/04