Multiple concurrent async ops per IoCtx?

Multiple concurrent async ops per IoCtx?

[Rutger ter Borg]

Dear list,

are Rados' IoCtx objects able to process multiple asynchronous 
operations at the same time, or is it necessary to wait for an operation 
to complete, before issuing a following operation?

I.e., can I do the following and expect it to work?

IoCtx ctx;
ctx.aio_read( ... read 1 ... );
ctx.aio_read( ... read 2 ... );
ctx.aio_read( ... read 3 ... );

... time passes ...

read 3 completes (e.g.)
read 1 completes
read 2 completes

TIA,
Cheers,

Rutger

qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Alexandre DERUMIER]

Hi, 

I'm trying to take a full vm state snapshot with savevm monitor command  (qemu 0.12rc1 + rbd 0.48.1)

it seem that vmstate is not saved in the snapshot. (I also don't notice any vm hang during snapshot)
Snapshot of disk is correctly made.



using loadvm monitor command, rollback correctly to disk snapshot but vm hang.


starting qemu with -loadvm snapshotname give
kvm: Error -22 while loading VM state


Is it normal ? Not implemented ?


Regards,

Alexandre

Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Smart Weblications GmbH - Florian Wiessner]

Am 29.08.2012 15:40, schrieb Alexandre DERUMIER:
> Hi, 
> 
> I'm trying to take a full vm state snapshot with savevm monitor command  (qemu 0.12rc1 + rbd 0.48.1)
> 

Have you tried qemu 1.1.1? 0.12 seems very old!


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Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Alexandre DERUMIER]

damn, I wanted to say, qemu 1.2rc1 ;)



----- Mail original ----- 

De: "Smart Weblications GmbH - Florian Wiessner" <f.wiessner@smart-weblications.de> 
À: "Alexandre DERUMIER" <aderumier@odiso.com> 
Cc: ceph-devel@vger.kernel.org 
Envoyé: Mercredi 29 Août 2012 15:48:05 
Objet: Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ? 

Am 29.08.2012 15:40, schrieb Alexandre DERUMIER: 
> Hi, 
> 
> I'm trying to take a full vm state snapshot with savevm monitor command (qemu 0.12rc1 + rbd 0.48.1) 
> 

Have you tried qemu 1.1.1? 0.12 seems very old! 


-- 

Mit freundlichen Grüßen, 

Florian Wiessner 

Smart Weblications GmbH 
Martinsberger Str. 1 
D-95119 Naila 

fon.: +49 9282 9638 200 
fax.: +49 9282 9638 205 
24/7: +49 900 144 000 00 - 0,99 EUR/Min* 
http://www.smart-weblications.de 

-- 
Sitz der Gesellschaft: Naila 
Geschäftsführer: Florian Wiessner 
HRB-Nr.: HRB 3840 Amtsgericht Hof 
*aus dem dt. Festnetz, ggf. abweichende Preise aus dem Mobilfunknetz 



-- 

-- 



	

Alexandre D e rumier 

Ingénieur Systèmes et Réseaux 


Fixe : 03 20 68 88 85 

Fax : 03 20 68 90 88 


45 Bvd du Général Leclerc 59100 Roubaix 
12 rue Marivaux 75002 Paris 

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Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Josh Durgin]

On 08/29/2012 06:40 AM, Alexandre DERUMIER wrote:
> Hi,
>
> I'm trying to take a full vm state snapshot with savevm monitor command  (qemu 0.12rc1 + rbd 0.48.1)
>
> it seem that vmstate is not saved in the snapshot. (I also don't notice any vm hang during snapshot)
> Snapshot of disk is correctly made.

AFAIK the only block backend that supports saving the vmstate is qcow2.
For rbd, the savevm/loadvm monitor commands are equivalent to
'rbd snap create' and 'rbd snap rollback'. They just save/rollback the
disk.

> using loadvm monitor command, rollback correctly to disk snapshot but vm hang.

If you don't quiesce i/o i.e. via xfsfreeze (it works on the vfs level
now, so it's not xfs-specific anymore) before snapshotting a running
vm, the fs might require a fsck to be usable. This is only rolling back
the disk, and not the memory state, so doing it while the vm is running
is likely to cause problems.

> starting qemu with -loadvm snapshotname give
> kvm: Error -22 while loading VM state
>
>
> Is it normal ? Not implemented ?

bdrv_{save|load}_vmstate are not implemented.

>
> Regards,
>
> Alexandre

Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Yehuda Sadeh]

On Wed, Aug 29, 2012 at 9:15 AM, Josh Durgin <josh.durgin@inktank.com> wrote:
> On 08/29/2012 06:40 AM, Alexandre DERUMIER wrote:
>>
>> Hi,
>>
>> I'm trying to take a full vm state snapshot with savevm monitor command
>> (qemu 0.12rc1 + rbd 0.48.1)
>>
>> it seem that vmstate is not saved in the snapshot. (I also don't notice
>> any vm hang during snapshot)
>> Snapshot of disk is correctly made.
>
>
> AFAIK the only block backend that supports saving the vmstate is qcow2.
> For rbd, the savevm/loadvm monitor commands are equivalent to
> 'rbd snap create' and 'rbd snap rollback'. They just save/rollback the
> disk.
>
>
>> using loadvm monitor command, rollback correctly to disk snapshot but vm
>> hang.
>
>
> If you don't quiesce i/o i.e. via xfsfreeze (it works on the vfs level
> now, so it's not xfs-specific anymore) before snapshotting a running
> vm, the fs might require a fsck to be usable. This is only rolling back
> the disk, and not the memory state, so doing it while the vm is running
> is likely to cause problems.
>
>
>> starting qemu with -loadvm snapshotname give
>> kvm: Error -22 while loading VM state
>>
>>
>> Is it normal ? Not implemented ?
>
>
> bdrv_{save|load}_vmstate are not implemented.
>
How complicated would it be to implement it? Looking at the api it
seems trivial. We can add a new block with a .vmstate prefix and keeps
the raw data on it. We should probably add some librbd functionality
that stores and retrieves alternative data payloads and use it for
that.

Yehuda

Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Josh Durgin]

On 08/29/2012 09:25 AM, Yehuda Sadeh wrote:
> On Wed, Aug 29, 2012 at 9:15 AM, Josh Durgin <josh.durgin@inktank.com> wrote:
>> On 08/29/2012 06:40 AM, Alexandre DERUMIER wrote:
>>>
>>> Hi,
>>>
>>> I'm trying to take a full vm state snapshot with savevm monitor command
>>> (qemu 0.12rc1 + rbd 0.48.1)
>>>
>>> it seem that vmstate is not saved in the snapshot. (I also don't notice
>>> any vm hang during snapshot)
>>> Snapshot of disk is correctly made.
>>
>>
>> AFAIK the only block backend that supports saving the vmstate is qcow2.
>> For rbd, the savevm/loadvm monitor commands are equivalent to
>> 'rbd snap create' and 'rbd snap rollback'. They just save/rollback the
>> disk.
>>
>>
>>> using loadvm monitor command, rollback correctly to disk snapshot but vm
>>> hang.
>>
>>
>> If you don't quiesce i/o i.e. via xfsfreeze (it works on the vfs level
>> now, so it's not xfs-specific anymore) before snapshotting a running
>> vm, the fs might require a fsck to be usable. This is only rolling back
>> the disk, and not the memory state, so doing it while the vm is running
>> is likely to cause problems.
>>
>>
>>> starting qemu with -loadvm snapshotname give
>>> kvm: Error -22 while loading VM state
>>>
>>>
>>> Is it normal ? Not implemented ?
>>
>>
>> bdrv_{save|load}_vmstate are not implemented.
>>
> How complicated would it be to implement it? Looking at the api it
> seems trivial. We can add a new block with a .vmstate prefix and keeps
> the raw data on it. We should probably add some librbd functionality
> that stores and retrieves alternative data payloads and use it for
> that.
>
> Yehuda
>

We probably wouldn't want to keep it in a single object, since it could
be very large, but it wouldn't be hard to reuse the regular I/O code to
stripe it across objects as well. It wouldn't be very complicated to
implement.

Josh

Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Alexandre DERUMIER]

Thanks Josh,

that's exactly what I want to know.

(BTW: I think that sheepdog block driver also support the save of the vmstate
http://lists.wpkg.org/pipermail/sheepdog/2010-April/000368.html
)

Regards,

Alexandre
----- Mail original ----- 

De: "Josh Durgin" <josh.durgin@inktank.com> 
À: "Alexandre DERUMIER" <aderumier@odiso.com> 
Cc: ceph-devel@vger.kernel.org 
Envoyé: Mercredi 29 Août 2012 18:15:17 
Objet: Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ? 

On 08/29/2012 06:40 AM, Alexandre DERUMIER wrote: 
> Hi, 
> 
> I'm trying to take a full vm state snapshot with savevm monitor command (qemu 0.12rc1 + rbd 0.48.1) 
> 
> it seem that vmstate is not saved in the snapshot. (I also don't notice any vm hang during snapshot) 
> Snapshot of disk is correctly made. 

AFAIK the only block backend that supports saving the vmstate is qcow2. 
For rbd, the savevm/loadvm monitor commands are equivalent to 
'rbd snap create' and 'rbd snap rollback'. They just save/rollback the 
disk. 

> using loadvm monitor command, rollback correctly to disk snapshot but vm hang. 

If you don't quiesce i/o i.e. via xfsfreeze (it works on the vfs level 
now, so it's not xfs-specific anymore) before snapshotting a running 
vm, the fs might require a fsck to be usable. This is only rolling back 
the disk, and not the memory state, so doing it while the vm is running 
is likely to cause problems. 

> starting qemu with -loadvm snapshotname give 
> kvm: Error -22 while loading VM state 
> 
> 
> Is it normal ? Not implemented ? 

bdrv_{save|load}_vmstate are not implemented. 

> 
> Regards, 
> 
> Alexandre 




-- 

-- 



	

Alexandre D e rumier 

Ingénieur Systèmes et Réseaux 


Fixe : 03 20 68 88 85 

Fax : 03 20 68 90 88 


45 Bvd du Général Leclerc 59100 Roubaix 
12 rue Marivaux 75002 Paris 
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Re: Multiple concurrent async ops per IoCtx?

[Josh Durgin]

On 08/29/2012 03:57 AM, Rutger ter Borg wrote:
>
> Dear list,
>
> are Rados' IoCtx objects able to process multiple asynchronous
> operations at the same time, or is it necessary to wait for an operation
> to complete, before issuing a following operation?
>
> I.e., can I do the following and expect it to work?
>
> IoCtx ctx;
> ctx.aio_read( ... read 1 ... );
> ctx.aio_read( ... read 2 ... );
> ctx.aio_read( ... read 3 ... );
>
> ... time passes ...
>
> read 3 completes (e.g.)
> read 1 completes
> read 2 completes
>
> TIA,
> Cheers,
>
> Rutger

Yes, all the asynchronous functions can run in parallel. An IoCtx
has little bearing on performance - it mostly just saves you from
specifying the full set of parameters (i.e. pool, snapshot id, snapshot
context, etc.) for each operation.

Are you seeing behavior that looks like the aio operations aren't being 
run in parallel?

Josh

Re: Multiple concurrent async ops per IoCtx?

[Rutger ter Borg]

On 2012-08-29 16:41, Josh Durgin wrote:

> Yes, all the asynchronous functions can run in parallel. An IoCtx
> has little bearing on performance - it mostly just saves you from
> specifying the full set of parameters (i.e. pool, snapshot id, snapshot
> context, etc.) for each operation.
>
> Are you seeing behavior that looks like the aio operations aren't being
> run in parallel?
>
> Josh

Thanks, that's all I wanted to check at this point!

Cheers,

Rutger