Open Stack

Agree with that, whatever the tweak inventory or traits, none of them works.

Same as VGPU, we can support pre-programmed mode for multiple-functions
region, and each region only can support one type function.

There are two reasons why Cyborg has a filter:
* records the usage of functions in a region
* records which function is programmed.

For #1, each region provider multiple functions. Each function can be
assigned to a VM. So we should create ResourceProvider for the region. And
the resource class is function. That is similar to the SR-IOV device. The
region(The PF)
provides functions (VFs).

For #2, We should use trait to distinguish the function type.

Then we didn't keep any inventory info in the cyborg again, and we needn't
any filter in cyborg also,
and there is no race condition anymore.

2018-03-29 2:48 GMT+08:00 Eric Fried <openstack at fried.cc>:

> Sundar-
>
>         We're running across this issue in several places right now.   One
> thing that's definitely not going to get traction is
> automatically/implicitly tweaking inventory in one resource class when
> an allocation is made on a different resource class (whether in the same
> or different RPs).
>
>         Slightly less of a nonstarter, but still likely to get significant
> push-back, is the idea of tweaking traits on the fly.  For example, your
> vGPU case might be modeled as:
>
> PGPU_RP: {
>   inventory: {
>       CUSTOM_VGPU_TYPE_A: 2,
>       CUSTOM_VGPU_TYPE_B: 4,
>   }
>   traits: [
>       CUSTOM_VGPU_TYPE_A_CAPABLE,
>       CUSTOM_VGPU_TYPE_B_CAPABLE,
>   ]
> }
>
>         The request would come in for
> resources=CUSTOM_VGPU_TYPE_A:1&required=VGPU_TYPE_A_CAPABLE, resulting
> in an allocation of CUSTOM_VGPU_TYPE_A:1.  Now while you're processing
> that, you would *remove* CUSTOM_VGPU_TYPE_B_CAPABLE from the PGPU_RP.
> So it doesn't matter that there's still inventory of
> CUSTOM_VGPU_TYPE_B:4, because a request including
> required=CUSTOM_VGPU_TYPE_B_CAPABLE won't be satisfied by this RP.
> There's of course a window between when the initial allocation is made
> and when you tweak the trait list.  In that case you'll just have to
> fail the loser.  This would be like any other failure in e.g. the spawn
> process; it would bubble up, the allocation would be removed; retries
> might happen or whatever.
>
>         Like I said, you're likely to get a lot of resistance to this idea
> as
> well.  (Though TBH, I'm not sure how we can stop you beyond -1'ing your
> patches; there's nothing about placement that disallows it.)
>
>         The simple-but-inefficient solution is simply that we'd still be
> able
> to make allocations for vGPU type B, but you would have to fail right
> away when it came down to cyborg to attach the resource.  Which is code
> you pretty much have to write anyway.  It's an improvement if cyborg
> gets to be involved in the post-get-allocation-candidates
> weighing/filtering step, because you can do that check at that point to
> help filter out the candidates that would fail.  Of course there's still
> a race condition there, but it's no different than for any other resource.
>
> efried
>
> On 03/28/2018 12:27 PM, Nadathur, Sundar wrote:
> > Hi Eric and all,
> >     I should have clarified that this race condition happens only for
> > the case of devices with multiple functions. There is a prior thread
> > <http://lists.openstack.org/pipermail/openstack-dev/2018-
> March/127882.html>
> > about it. I was trying to get a solution within Cyborg, but that faces
> > this race condition as well.
> >
> > IIUC, this situation is somewhat similar to the issue with vGPU types
> > <http://eavesdrop.openstack.org/irclogs/%23openstack-nova/
> %23openstack-nova.2018-03-27.log.html#t2018-03-27T13:41:00>
> > (thanks to Alex Xu for pointing this out). In the latter case, we could
> > start with an inventory of (vgpu-type-a: 2; vgpu-type-b: 4).  But, after
> > consuming a unit of  vGPU-type-a, ideally the inventory should change
> > to: (vgpu-type-a: 1; vgpu-type-b: 0). With multi-function accelerators,
> > we start with an RP inventory of (region-type-A: 1, function-X: 4). But,
> > after consuming a unit of that function, ideally the inventory should
> > change to: (region-type-A: 0, function-X: 3).
> >
> > I understand that this approach is controversial :) Also, one difference
> > from the vGPU case is that the number and count of vGPU types is static,
> > whereas with FPGAs, one could reprogram it to result in more or fewer
> > functions. That said, we could hopefully keep this analogy in mind for
> > future discussions.
> >
> > We probably will not support multi-function accelerators in Rocky. This
> > discussion is for the longer term.
> >
> > Regards,
> > Sundar
> >
> > On 3/23/2018 12:44 PM, Eric Fried wrote:
> >> Sundar-
> >>
> >>      First thought is to simplify by NOT keeping inventory information
> in
> >> the cyborg db at all.  The provider record in the placement service
> >> already knows the device (the provider ID, which you can look up in the
> >> cyborg db) the host (the root_provider_uuid of the provider representing
> >> the device) and the inventory, and (I hope) you'll be augmenting it with
> >> traits indicating what functions it's capable of.  That way, you'll
> >> always get allocation candidates with devices that *can* load the
> >> desired function; now you just have to engage your weigher to prioritize
> >> the ones that already have it loaded so you can prefer those.
> >>
> >>      Am I missing something?
> >>
> >>              efried
> >>
> >> On 03/22/2018 11:27 PM, Nadathur, Sundar wrote:
> >>> Hi all,
> >>>     There seems to be a possibility of a race condition in the
> >>> Cyborg/Nova flow. Apologies for missing this earlier. (You can refer to
> >>> the proposed Cyborg/Nova spec
> >>> <https://review.openstack.org/#/c/554717/1/doc/specs/rocky/
> cyborg-nova-sched.rst>
> >>> for details.)
> >>>
> >>> Consider the scenario where the flavor specifies a resource class for a
> >>> device type, and also specifies a function (e.g. encrypt) in the extra
> >>> specs. The Nova scheduler would only track the device type as a
> >>> resource, and Cyborg needs to track the availability of functions.
> >>> Further, to keep it simple, say all the functions exist all the time
> (no
> >>> reprogramming involved).
> >>>
> >>> To recap, here is the scheduler flow for this case:
> >>>
> >>>   * A request spec with a flavor comes to Nova conductor/scheduler. The
> >>>     flavor has a device type as a resource class, and a function in the
> >>>     extra specs.
> >>>   * Placement API returns the list of RPs (compute nodes) which contain
> >>>     the requested device types (but not necessarily the function).
> >>>   * Cyborg will provide a custom filter which queries Cyborg DB. This
> >>>     needs to check which hosts contain the needed function, and filter
> >>>     out the rest.
> >>>   * The scheduler selects one node from the filtered list, and the
> >>>     request goes to the compute node.
> >>>
> >>> For the filter to work, the Cyborg DB needs to maintain a table with
> >>> triples of (host, function type, #free units). The filter checks if a
> >>> given host has one or more free units of the requested function type.
> >>> But, to keep the # free units up to date, Cyborg on the selected
> compute
> >>> node needs to notify the Cyborg API to decrement the #free units when
> an
> >>> instance is spawned, and to increment them when resources are released.
> >>>
> >>> Therein lies the catch: this loop from the compute node to controller
> is
> >>> susceptible to race conditions. For example, if two simultaneous
> >>> requests each ask for function A, and there is only one unit of that
> >>> available, the Cyborg filter will approve both, both may land on the
> >>> same host, and one will fail. This is because Cyborg on the controller
> >>> does not decrement resource usage due to one request before processing
> >>> the next request.
> >>>
> >>> This is similar to this previous Nova scheduling issue
> >>> <https://specs.openstack.org/openstack/nova-specs/specs/
> pike/implemented/placement-claims.html>.
> >>> That was solved by having the scheduler claim a resource in Placement
> >>> for the selected node. I don't see an analog for Cyborg, since it would
> >>> not know which node is selected.
> >>>
> >>> Thanks in advance for suggestions and solutions.
> >>>
> >>> Regards,
> >>> Sundar
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> ____________________________________________________________
> ______________
> >>> OpenStack Development Mailing List (not for usage questions)
> >>> Unsubscribe: OpenStack-dev-request at lists.openstack.org?subject:
> unsubscribe
> >>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> >>>
> >> ____________________________________________________________
> ______________
> >> OpenStack Development Mailing List (not for usage questions)
> >> Unsubscribe: OpenStack-dev-request at lists.openstack.org?subject:
> unsubscribe
> >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> >
> >
> >
> > ____________________________________________________________
> ______________
> > OpenStack Development Mailing List (not for usage questions)
> > Unsubscribe: OpenStack-dev-request at lists.openstack.org?subject:
> unsubscribe
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> >
>
> __________________________________________________________________________
> OpenStack Development Mailing List (not for usage questions)
> Unsubscribe: OpenStack-dev-request at lists.openstack.org?subject:unsubscribe
> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstack.org/pipermail/openstack-dev/attachments/20180329/499cbc59/attachment.html>