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Hi Phil,

The nova.db.api.compute_node_update() call is what the individual virt
drivers call to update the compute node stats. grep for that and you'll
see where the calls to set the compute node data are called.

Best,
-jay

On 07/13/2012 09:38 AM, Day, Phil 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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