On 06/06/2014 08:07 AM, Murray, Paul (HP Cloud) wrote:
Forcing an instance to a specific host is very useful for the
operator - it fulfills a valid use case for monitoring and testing
purposes.
Pray tell, what is that valid use case?
I am not defending a particular way of doing this, just
bringing up that it has to be handled. The effect on limits is purely
implementation - no limits get set so it by-passes any resource
constraints, which is deliberate.
-----Original Message----- From: Jay Pipes
[mailto:jaypi...@gmail.com] Sent: 04 June 2014 19:17 To:
openstack-dev@lists.openstack.org Subject: Re: [openstack-dev] [nova]
Proposal: Move CPU and memory allocation ratio out of scheduler
On 06/04/2014 06:10 AM, Murray, Paul (HP Cloud) wrote:
Hi Jay,
This sounds good to me. You left out the part of limits from the
discussion - these filters set the limits used at the resource
tracker.
Yes, and that is, IMO, bad design. Allocation ratios are the domain
of the compute node and the resource tracker. Not the scheduler. The
allocation ratios simply adjust the amount of resources that the
compute node advertises to others. Allocation ratios are *not*
scheduler policy, and they aren't related to flavours.
You also left out the force-to-host and its effect on limits.
force-to-host is definitively non-cloudy. It was a bad idea that
should never have been added to Nova in the first place.
That said, I don't see how force-to-host has any affect on limits.
Limits should not be output from the scheduler. In fact, they
shouldn't be anything other than an *input* to the scheduler,
provided in each host state struct that gets built from records
updated in the resource tracker and the Nova database.
Yes, I would agree with doing this at the resource tracker too.
And of course the extensible resource tracker is the right way to
do it J
:) Yes, clearly this is something that I ran into while brainstorming
around the extensible resource tracker patches.
Best, -jay
Paul.
*From:*Jay Lau [mailto:jay.lau....@gmail.com] *Sent:* 04 June 2014
10:04 *To:* OpenStack Development Mailing List (not for usage
questions) *Subject:* Re: [openstack-dev] [nova] Proposal: Move CPU
and memory allocation ratio out of scheduler
Does there is any blueprint related to this? Thanks.
2014-06-03 21:29 GMT+08:00 Jay Pipes <jaypi...@gmail.com
<mailto:jaypi...@gmail.com>>:
Hi Stackers,
tl;dr =====
Move CPU and RAM allocation ratio definition out of the Nova
scheduler and into the resource tracker. Remove the calculations
for overcommit out of the core_filter and ram_filter scheduler
pieces.
Details =======
Currently, in the Nova code base, the thing that controls whether
or not the scheduler places an instance on a compute host that is
already "full" (in terms of memory or vCPU usage) is a pair of
configuration options* called cpu_allocation_ratio and
ram_allocation_ratio.
These configuration options are defined in, respectively,
nova/scheduler/filters/core_filter.py and
nova/scheduler/filters/ram_filter.py.
Every time an instance is launched, the scheduler loops through a
collection of host state structures that contain resource
consumption figures for each compute node. For each compute host,
the core_filter and ram_filter's host_passes() method is called. In
the host_passes() method, the host's reported total amount of CPU
or RAM is multiplied by this configuration option, and the product
is then subtracted from the reported used amount of CPU or RAM. If
the result is greater than or equal to the number of vCPUs needed
by the instance being launched, True is returned and the host
continues to be considered during scheduling decisions.
I propose we move the definition of the allocation ratios out of
the scheduler entirely, as well as the calculation of the total
amount of resources each compute node contains. The resource
tracker is the most appropriate place to define these configuration
options, as the resource tracker is what is responsible for keeping
track of total and used resource amounts for all compute nodes.
Benefits:
* Allocation ratios determine the amount of resources that a
compute node advertises. The resource tracker is what determines
the amount of resources that each compute node has, and how much of
a particular type of resource have been used on a compute node. It
therefore makes sense to put calculations and definition of
allocation ratios where they naturally belong. * The scheduler
currently needlessly re-calculates total resource amounts on every
call to the scheduler. This isn't necessary. The total resource
amounts don't change unless either a configuration option is
changed on a compute node (or host aggregate), and this calculation
can be done more efficiently once in the resource tracker. * Move
more logic out of the scheduler * With the move to an extensible
resource tracker, we can more easily evolve to defining all
resource-related options in the same place (instead of in different
filter files in the scheduler...)
Thoughts?
Best, -jay
* Host aggregates may also have a separate allocation ratio that
overrides any configuration setting that a particular host may
have
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Thanks,
Jay
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