[Engine-devel] CPU Pinning @engine

[Doron Fediuck]

On 21/05/12 11:16, Yaniv Kaul wrote:
> On 05/21/2012 11:08 AM, Doron Fediuck wrote:
>> On 21/05/12 11:01, Dor Laor wrote:
>>> On 05/21/2012 10:58 AM, Doron Fediuck wrote:
>>>> On 21/05/12 01:45, Andrew Cathrow wrote:
>>>>>
>>>>> ----- Original Message -----
>>>>>> From: "Doron Fediuck"<dfediuck at redhat.com>
>>>>>> To: dlaor at redhat.com
>>>>>> Cc: engine-devel at ovirt.org
>>>>>> Sent: Sunday, May 20, 2012 5:49:08 PM
>>>>>> Subject: Re: [Engine-devel] CPU Pinning @engine
>>>>>>
>>>>>> On 20/05/12 21:41, Dor Laor wrote:
>>>>>>> On 05/17/2012 11:15 PM, Doron Fediuck wrote:
>>>>>>>> On 17/05/12 20:28, Ayal Baron wrote:
>>>>>>>>> "Live migration will not be supported for such VM's."
>>>>>>>>>
>>>>>>>>> Migration will work on homogeneous clusters so this should not be
>>>>>>>>> enforced (not limited to VMs which are pinned to host) just give
>>>>>>>>> a warning.
>>>>>>>>>
>>>>>>>> I agree, but if we wish to ping vCPUx to pCPUy in host a, we
>>>>>>>> cannot ensure to have the same in host b,
>>>>>>>> since it may have pCPUy too busy, so performance will degrade.
>>>>>>>> Also, I hope you saw my general comment
>>>>>>> Performance may degrade on any migration to loaded host regardless
>>>>>>> of pinning.
>>>>>>>
>>>>>>> There is not need to forbid migration. Instead, the SLA assurance
>>>>>>> policy should verify the dedicated resources and match the target
>>>>>>> w/ the guarantee and decide according to this.
>>>>>>>
>>>>>> Thanks for the input.
>>>>>> We may start with migration blocked in a configurable manner, so
>>>>>> people who wish migrate to work
>>>>>> will simply set the relevant configuration key.
>>>>>> As for looking for a matched CPU, will add it as p2.
>>>>> We shouldn't block migration
>>>>> If a user wants to not migrate a cpu pinned VM then let them use the non-migratable flag in the UI.
>>>>>
>>>> We're not blocking migration, we're allowing pinning (for now) only for non-migrative VM's.
>>>> For p2 we'll verify destination host has the relevant pinning capacity, which will allow
>>>> pinning for migrative VM's as well.
>>>
>>> IMHO the order should be the opposite - if the user likes to migrate a pinned VM, let him (you can pop some message if you like).
>> I'll check it with UI guys (AFAIK engine UI has no pop-ups).
>> Also, I prefer safe than sorry. So start with a safe working pinning for pinned-to-host VMs, and then push the envelope.
> 
> Safe is letting the user migrate. It may or may not succeed (I'd worry it may put a host into Error state - I hope we've removed this state).
This is a pure speculation. If I'm pinning a specific VM to a specific host, and its vCPUS into specific pCPUs, 
how can live migration be considered a safe thing? If I pinned to host, this is a violation of my request. Now, let's say
I didn't pin to host, but I ask for specific vCPUS pinning into specific pCPUs. For now, there's no guarantee the destination
host will have a relevant CPU capacity (maybe even topology), so CPU pinning may not work, which is also a violation of
my request. Is live migration really the safe thing to do here??? Why not alert me so I could manually migrate to where I think
is better?
Having that said, I'm reminding you the somewhere earlier in this thread I wrote we'll make the constraint of cpu pinning
allowed only on pinned-to-host VMs configurable, so people who wish to walk on wild side, can give it a go.

> Sorry is when you wish you had done so initially.  ;-)
In this case, I disagree as this is configurable.

> Y.
> 
> 
>>
>>>>>>>> about starting with a humble solution and gradually improving. In
>>>>>>>> this context (auto)numa can help us,
>>>>>>>> so we better do numa than handle migration for basic mode, risking
>>>>>>>> performance issues.
>>>>>>>>
>>>>>>>>> ----- Original Message -----
>>>>>>>>>> From: "Doron Fediuck"<dfediuck at redhat.com>
>>>>>>>>>> To: engine-devel at ovirt.org
>>>>>>>>>> Sent: Thursday, May 17, 2012 2:42:46 PM
>>>>>>>>>> Subject: [Engine-devel] CPU Pinning @engine
>>>>>>>>>>
>>>>>>>>>> Hi All,
>>>>>>>>>> Currently the VDSM has a CPU pinning hook.
>>>>>>>>>> We'd like to add better support of it into the engine itself.
>>>>>>>>>> Here's a design draft to cover it:
>>>>>>>>>> http://www.ovirt.org/wiki/Features/Design/cpu-pinning
>>>>>>>>>>
>>>>>>>>>> Please review and comment if needed.
>>>>>>>>>>
>>>>>>>>>> Thanks!
>>>>>>>>>> -- 
>>>>>>>>>>
>>>>>>>>>> /d
>>>>>>>>>>
>>>>>>>>>> Never say "OOPS!" always say "Ah, Interesting!"
>>>>>>>>>> _______________________________________________
>>>>>>>>>> Engine-devel mailing list
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>>>>>>>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
>>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> Engine-devel mailing list
>>>>>>>>> Engine-devel at ovirt.org
>>>>>>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
>>>>>>>>
>>>>>>
>>>>>> -- 
>>>>>>
>>>>>> /d
>>>>>>
>>>>>> Never say "OOPS!" always say "Ah, Interesting!"
>>>>>> _______________________________________________
>>>>>> Engine-devel mailing list
>>>>>> Engine-devel at ovirt.org
>>>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
>>>>>>
>>>>
>>
> 


-- 

/d

Why doesn't DOS ever say "EXCELLENT command or filename!"