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Well, I don't know what John means by "modify the over-commit calculation in the scheduler", so I cannot comment. 

The idea of choosing free host for Hadoop on the fly is rather complicated and contains several operations, namely: (1) assuring the host never get pass 100% CPU load; (2) identifying a host that already has a Hadoop VM running on it, or already 100% CPU commitment; (3) releasing the host from 100% CPU commitment once the Hadoop VM stops; (4) possibly avoiding other applications to use the host (to economy the host resource). 

- You'll need (1) because otherwise your Hadoop VM would come short of resources after the host gets overloaded. 
- You'll need (2) because you don't want to restrict a new host while one of your 100% CPU commited hosts still has free resources. 
- You'll need (3) because otherwise you host would be forerever restricted, and that is no longer "on the fly". 
- You'll may need (4) because otherwise it'd be a waste of resources. 

The problem of changing CPU overcommit on the fly is that when your Hadoop VM is still running, someone else can add another VM in the same host with a higher CPU overcommit (e.g. 200%), (violating (1) ) thus effecting your Hadoop VM also. 
The idea of putting the host in the aggregate can give you (1) and (2). (4) is done by AggregateInstanceExtraSpecsFilter. However, it does not give you (3); which can be done with pCloud. 


----- Original Message -----

From: "Alexander Kuznetsov" <akuznetsov at mirantis.com> 
To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org> 
Sent: Wednesday, November 13, 2013 3:09:40 PM 
Subject: Re: [openstack-dev] [nova] Configure overcommit policy 

Toan and Alex. Having separate computes pools for Hadoop is not suitable if we want to use an unused power of OpenStack cluster to run Hadoop analytic jobs. Possibly in this case it is better to modify the over-commit calculation in the scheduler according John suggestion. 


On Tue, Nov 12, 2013 at 7:16 PM, Khanh-Toan Tran < khanh-toan.tran at cloudwatt.com > wrote: 



FYI, by default Openstack overcommit CPU 1:16, meaning it can host 16 times number of cores it possesses. As mentioned Alex, you can change it by enabling AggregateCoreFilter in nova.conf: 
scheduler_default_filters = <list of your filters, adding AggregateCoreFilter here> 

and modifying the overcommit ratio by adding: 
cpu_allocation_ratio=1.0 

Just a suggestion, think of isolating the host for the tenant that uses Hadoop so that it will not serve other applications. You have several filters at your disposal: 
AggregateInstanceExtraSpecsFilter 
IsolatedHostsFilter 
AggregateMultiTenancyIsolation 

Best regards, 

Toan 


From: "Alex Glikson" < GLIKSON at il.ibm.com > 

To: "OpenStack Development Mailing List (not for usage questions)" < openstack-dev at lists.openstack.org > 
Sent: Tuesday, November 12, 2013 3:54:02 PM 

Subject: Re: [openstack-dev] [nova] Configure overcommit policy 

You can consider having a separate host aggregate for Hadoop, and use a combination of AggregateInstanceExtraSpecFilter (with a special flavor mapped to this host aggregate) and AggregateCoreFilter (overriding cpu_allocation_ratio for this host aggregate to be 1). 

Regards, 
Alex 




From: John Garbutt < john at johngarbutt.com > 
To: "OpenStack Development Mailing List (not for usage questions)" < openstack-dev at lists.openstack.org >, 
Date: 12/11/2013 04:41 PM 
Subject: Re: [openstack-dev] [nova] Configure overcommit policy 




On 11 November 2013 12:04, Alexander Kuznetsov < akuznetsov at mirantis.com > wrote: 
> Hi all, 
> 
> While studying Hadoop performance in a virtual environment, I found an 
> interesting problem with Nova scheduling. In OpenStack cluster, we have 
> overcommit policy, allowing to put on one compute more vms than resources 
> available for them. While it might be suitable for general types of 
> workload, this is definitely not the case for Hadoop clusters, which usually 
> consume 100% of system resources. 
> 
> Is there any way to tell Nova to schedule specific instances (the ones which 
> consume 100% of system resources) without overcommitting resources on 
> compute node? 

You could have a flavor with "no-overcommit" extra spec, and modify 
the over-commit calculation in the scheduler on that case, but I don't 
remember seeing that in there. 

John 

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