Open Stack

Hey Phil,

As Chris mentioned, I do have another review up: https://review.openstack.org/#/c/9402/

The goal with that one is to more completely calculate all the capacity and resource consumption information on the compute host than the current capacity_notifier does.  So, capacity-based scheduling is not going anywhere, I'm just working on getting more up-to-date and useful information to the scheduler via the same ComputeNode model structure.  Having accurate and timely information on the scheduler side (via ComputeNode) will reduce the number of races when there are multiple schedulers running.  However, because it is a distributed system with non-zero latency and there are no guarantees but death & taxes, the rescheduling patch exists to complement this: https://review.openstack.org/#/c/9540/

As far as the current code goes in capacity_notifier goes, it is confusing, and I'm not sure the comments you mentioned are in sync with the scheduler's current reality.  Capacity notifier is removed in https://review.openstack.org/#/c/9402/ and the logic is moved to the ResourceTracker class.  There are no changes to the ComputeNode model itself, just the process of populating its values.

Thanks,
Brian

On Jul 13, 2012, at 4:06 PM, Chris Behrens wrote:

> Capacity based scheduling currently adds up all instance usage in host_manager.py
> 
> There's another review marked as WIP that will be ready when retries go in that cleans that and the capacity tracking up.  Look for it from Brian Elliott.
> 
> On Jul 13, 2012, at 6:38 AM, "Day, Phil" <philip.day at hp.com> wrote:
> 
>> Hi Folks,
>>  
>> I was reviewing a code change to add generic retries for build failures ( https://review.openstack.org/#/c/9540/2 ), and wanted to be sure that it wouldn’t invalidate the capacity accounting used by the scheduler.
>>  
>> However I've been sitting here for a while working through the Folsom scheduler code trying to understand how the capacity based scheduling now works, and I’m sure I’m missing something obvious but I just can’t work out where the free_ram_mb value in the compute_node table gets updated.
>>  
>> I can see the database api method to update the values, compute_node_utilization_update(),  it doesn’t look as if anything in the code ever calls that ?
>>  
>> From when I last looked at this / various discussions here and at the design summits I thought the approach was that:
>> -          The scheduler would make a call (rather than a cast) to the compute manger, which would then do some verification work, update the DB table whilst in the context of that call, and then start a thread to complete the spawn.  The need to go all the way to the compute node as a call was to avoid race conditions from multiple schedulers.  (the change I’m looking at is part of a blueprint to avoid such a race, so maybe I imagined the change from cast to call ?)
>>  
>> -          On a delete, the capacity_notifer (which had to be configured into the list_notifier) would detect the delete message, and decrement the database values.
>>  
>> But now I look through the code it looks as if the scheduler is still doing a cast (scheduler/driver),  and although I can see the database api call to update the values, compute_node_utilization_update(),  it doesn’t look as if anything in the code ever calls that ?
>>  
>> The ram_filter scheduler seems to use the free_ram_mb value, and that value seems to come from the host_manager in the scheduler which is read from the Database,  but I can't for the life of me work out where these values are updated in the Database.
>>  
>> The capacity_notifier, which used to decrement values on a VM deletion only (according to the comments the increment was done in the scheduler) seems to have now disappeared altogether in the move of the notifier to openstack/common ?
>>  
>> So I’m sure I’m missing some other even more cunning plan on how to keep the values current, but I can’t for the life of me work out what it is – can someone fill me in please ?
>>  
>> Thanks,
>> Phil
>>  
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