----- Original Message -----
> On 12/08/2011 12:33 PM, Ayal Baron wrote:
> >
> >
> > ----- Original Message -----
> >> On Tue, Dec 06, 2011 at 12:42:24PM +0200, Dor Laor wrote:
> >>> On 12/05/2011 03:55 PM, Adam Litke wrote:
> >>>> On Sun, Dec 04, 2011 at 11:07:43PM +0200, Dor Laor wrote:
> >>>>> On 12/02/2011 04:15 PM, Adam Litke wrote:
> >>>>>> On Fri, Dec 02, 2011 at 03:08:24AM +0200, Dan Kenigsberg
> >>>>>> wrote:
> >>>>>>> On Thu, Dec 01, 2011 at 11:05:55AM +0200, Dor Laor wrote:
> >>>>>>>> On 11/29/2011 06:29 PM, Adam Litke wrote:
> >>>>>>>>> After discussing MOM / VDSM integration at length, two
> >>>>>>>>> different strategies have
> >>>>>>>>> emerged.  I will call them Plan A and Plan B:
> >>>>>>>>>
> >>>>>>>>> Plan A: MOM integration at the OS/Packaging level
> >>>>>>>>> Plan B: MOM integration as a new VDSM thread
> >>>>>>>>
> >>>>>>>> I think a form of plan B is more appropriate:
> >>>>>>>>
> >>>>>>>> In general we can look at MOM vs VDSM just like micro kernel
> >>>>>>>> vs linux
> >>>>>>>> kernel approach. MOM can be independent project but then it
> >>>>>>>> will need to
> >>>>>>>> expose much more apis for VDSM and wise verse.
> >>>>>>>>
> >>>>>>>> For example, take live migration, there is no point of MOM
> >>>>>>>> balloon a
> >>>>>>>> guest while it is migrating. So either you ignore that which
> >>>>>>>> is bad or
> >>>>>>>> now need to listen to VDSM events on VM migration.
> >>>>>>>>
> >>>>>>>> Think about hot plug vcpu/pci-device to a VM - if before MOM
> >>>>>>>> used some
> >>>>>>>> SLA for the VM, now it will need to change to cope w/ the
> >>>>>>>> new
> >>>>>>>> resources,
> >>>>>>>> again more api/events for that.
> >>>>>>>>
> >>>>>>>> Another thing - all of the settings for per VM
> >>>>>>>> KSM/THP/Swap/Balloon -
> >>>>>>>> all will need to propagate from the vdsm api towards MOM.
> >>>>>>>
> >>>>>>> Indeed, disagreement is much more interesting! I think that
> >>>>>>> the
> >>>>>>> information
> >>>>>>> that Vdsm is expected to provide to momd is quite limitted
> >>>>>>> and
> >>>>>>> slowly-changing.
> >>>>>>> We may be better off defining an API for Vdsm to notify momd
> >>>>>>> of
> >>>>>>> VM state
> >>>>>>> changes, than to entangle mom within Vdsm.
> >>>>>>
> >>>>>> Yep.  We will need to write a MOM GuestVDSM Collector in order
> >>>>>> to gather
> >>>>>> statistics from vdsm guests.  This Collector could also fetch
> >>>>>> guest events using
> >>>>>> the vdsm API.
> >>>>>>
> >>>>>
> >>>>> All these APIs are nice and required regardless if vdsm hosts
> >>>>> MOM
> >>>>> or
> >>>>> MOM is independent. Still, there is a *huge* difference in
> >>>>> terms
> >>>>> of
> >>>>> development speed and overhead by committing to external APIs.
> >>>>>
> >>>>> Correct me if I'm wrong but the only value of keeping MOM
> >>>>> separate
> >>>>> is that it will be used as a general purpose policy tool for
> >>>>> the
> >>>>> OS.
> >>>>
> >>>> This is one advantage, but cetainly not the only one.  More
> >>>> importantly, as
> >>>> pointed out by Dan K. and Dan B., keeping it separate will
> >>>> encourage
> >>>> modularization which is greatly needed in vdsm.  As part of this
> >>>> modularization,
> >>>> it will be easier to see, specifically, what MOM is allowed to
> >>>> do;
> >>>> making
> >>>> writing a SELinux policy for the policy engine much easier.
> >>>
> >>> It's not a reason to commit to two separate remote APIs that will
> >>> be
> >>> supported for a very long period.
> >>> Modularization and internal apis should be achieved regardless.
> >>> Moreover, since there is no modularization today, committing too
> >>> early for new apis might cause us pains in the future.
> >>>
> >>> So my offer is to do the modularization and define apis between
> >>> mom
> >>> and vdsm but keep all internal. After a year we'll be able to
> >>> judge
> >>> whether we got the right set and might be worth to spin off MOM.
> >>
> >> We let's give this plan a try.  Based on other planning and
> >> dicussions, vdsm is
> >> going to gain quite a few new threads: QMF agent threads, REST API
> >> server
> >> threads, MOM threads.  A good place to start poking might be to
> >> ensure that we
> >> can handle the additional complexity that comes with these extra
> >> threads.
> >
> > Which plan?
> 
> A plan of first hosting MOM inside VDSM w/o committing to support
> public
> APIs. After definition/stabilization period it will be
> possible/sensible
> to spin off MOM for independence.
> 
> AFAIK, Dan and Adam are on board this plan, I can't understand from
> the
> email what's your opinion about it.
> 
> It doesn't matter how small you might keep MOM, it will take time to
> define the right APIs and to commit for long term support. If
> miraculously one might manage to do this really fast, then no problem
> at
> all. Reading previous posts, it seems like VDSM will get benefit of
> that
> too for its internal APIs

we can build it as a library from the get go, that would immediately make sure 
we're passing things the right way and it wouldn't mean that mom has to commit 
to a stable API.
My take on it is that we shouldn't integrate with yet another daemon competing 
on the same resources (VMs) and that full integration as part of vdsm is wrong 
as well.

> 
> 
> > In general, I think that Mom APIs should be kept separate from vdsm
> > and vdsm would interact with a public mom API. On the other hand,
> > I do not think mom should be a daemon as that quickly leads to it
> > keeping a lot of state that needs to be synchronized between vdsm
> > and mom.
> > You gave libvirt as an example, but it is a very bad one as the
> > architecture there is sub par at most.  Suffice it to see that the
> > #loc when vdsm communicated directly with qemu was smaller than it
> > is now going through libvirt without additional direct
> > functionality (there is a lot that we gained using libvirt in the
> > form of svirt and other configurations libvirt does, but this
> > should not have affected the integration at all).
> > The reason for the code bloat is having to synchronize 2 stateful
> > daemons.  I believe that were libvirt actually a lib things would
> > have been much simpler and more straight-forward.
> > I think the same applies to mom.
> >
> > Because mom is a generic policy engine then it stands to reason
> > that any mom-client would want the following:
> >
> > 1. send mom client's current state and rules/policy
> > 2. mom would compute required state changes
> > 3. run client specific changes.
> >
> > Doing number 3 would require either integrating with the client's
> > public API or just pass back to the client a list of required
> > changes and have it execute them.
> > I don't think that using the public API in this scenario is the
> > right thing to do.
> >
> > I think that the current mom implementation mixes the client and
> > the engine functionality.
> > If you separate current mom into 2 projects, the rule engine and
> > the rest (data collectors and execution of actions) you will find
> > that the engine needs no special privileges at all.
> > The current mapping problem is that you're trying to use the client
> > you already wrote with vdsm which is wrong, as vdsm already has
> > collectors of its own and knows the problem specific actions that
> > it can run.  The confusion stems from the fact that the problem
> > domain is the same (throttling VMs).
> >
> >
> >>
> >> --
> >> Adam Litke<a...@us.ibm.com>
> >> IBM Linux Technology Center
> >>
> >> _______________________________________________
> >> vdsm-devel mailing list
> >> vdsm-devel@lists.fedorahosted.org
> >> https://fedorahosted.org/mailman/listinfo/vdsm-devel
> >>
> 
> 
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