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Re: [Qemu-devel] [PATCH 1/2] Add virtagent file system freeze/thaw
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] Add virtagent file system freeze/thaw |
Date: |
Tue, 1 Feb 2011 14:34:19 +0000 |
On Tue, Feb 1, 2011 at 2:26 PM, Jes Sorensen <address@hidden> wrote:
> On 02/01/11 15:12, Stefan Hajnoczi wrote:
>> On Tue, Feb 1, 2011 at 10:58 AM, <address@hidden> wrote:
>>> From: Jes Sorensen <address@hidden>
>>>
>>> Implement freeze/thaw support in the guest, allowing the host to
>>> request the guest freezes all it's file systems before a live snapshot
>>> is performed.
>>> - fsfreeze(): Walk the list of mounted local real file systems,
>>> and freeze them.
>>> - fsthaw(): Walk the list of previously frozen file systems and
>>> thaw them.
>>> - fsstatus(): Return the current status of freeze/thaw. The host must
>>> poll this function, in case fsfreeze() returned with a
>>> timeout, to wait for the operation to finish.
>>
>> It is desirable to minimize the freeze time, which may interrupt or
>> degrade the service that applications inside the VM can provide.
>> Polling means we have to choose a fixed value (500 ms?) at which to
>> check for freeze completion. In this example we could have up to 500
>> ms extra time spent in freeze because it completed right after we
>> polled. Any thoughts on this?
>
> I have to admit you lost me here, where do you get that 500ms time from?
> Is that the XMLRPC polling time or? I just used the example code from
> other agent calls.
500 ms is made up. I was thinking, "what would a reasonable polling
interval be?" and picked a sub-second number.
Can you explain how the timeout in fsfreeze can happen? It's probably
because I don't know the virtagent details.
Stefan
[Qemu-devel] Re: [PATCH 1/2] Add virtagent file system freeze/thaw, Adam Litke, 2011/02/01
[Qemu-devel] Re: [PATCH 1/2] Add virtagent file system freeze/thaw, Michael Roth, 2011/02/01
Re: [Qemu-devel] [PATCH 1/2] Add virtagent file system freeze/thaw, Stefan Hajnoczi, 2011/02/02