On 02/23/2018 02:04 PM, Han Zhou wrote:
Hi Mark, thank you very much for the feedback!!

On Fri, Feb 23, 2018 at 10:56 AM, Mark Michelson <mmich...@redhat.com <mailto:mmich...@redhat.com>> wrote:
 > Hi Han,
> First off, great work! This is fantastic to see, and I'm super excited to see such a drop in CPU usage with this patch.
> Since this is an RFC patch, I won't go too deep into nitty-gritty details on this. Rather, I'll look at it from a high level.
> The API design idea is great. I like the use of a directed graph since it clearly indicates dependencies. The patch progression is done really well since it allows for us to easily understand each individual change. It also makes it easy to see additional incremental changes that could be added in the future.
> My main concern is that the specific setup you have used here results in data encapsulation not being very strong. For instance, the en_flow_output node consistently looks inside the en_runtime_data node for input data. It appears from my quick look that en_flow_output is treating this data as immutable, but I'm not 100% sure if I'm correct. There's nothing in place to stop it from modifying that data if it wanted to, though.

Agree. It is also my concern for the lack of strong encapsulation. The principle to follow is that each node take input node data as immutable, and write its own data. I will think about how to make this explicitly from code perspective. I didn't have a good idea on this. Do you have any suggestion?
One thought is that we could create better delineations between the working data of a node and its output data. In other words, there could be one structure of mutable data that the node can manipulate, and a separate structure of const data that it exports for other nodes to read. Right now, there is a function called engine_get_input() that retrieves an engine_node. Maybe a better idea would be to replace that with something like engine_get_input_data() that retrieves read-only data from an engine node instead.

> Also it is common for nodes to modify global data rather than just modifying node-local data(e.g. making calls to ofctrl_add_flow(), which modifies a global hmap).

flow-table can be considered as data of en_flow_output. Since en_flow_output is the leaf node of the DAG and no other engine node depends on it, so I didn't think it is quit necessary to maintain its own local data. But I agree it is better to be clear from the engine node perspective. I can move the flow-table to en_flow_output data, and update ofctrl module as consumer of that data.

> Ideally, this entire thing would be doable without the need for the engine_get_input() function. Each node would operate independently on its own data. Doing this would aid in the ability to reason about what each node is responsible for, and it would open the door for introducing parallel processing of sibling nodes in the DAG.

Sorry that I didn't get this point. Each node would operate on its own data but they also depends on their inputs, and that's why engine_get_input() is here for. Did I misunderstand your point?

I think taking a second look at the patch has made things a bit more clear for me. In my initial reading, I thought that engine_get_input() was an anti-pattern since it was being used to look into the "private" data of another node. Now that I look again, it makes more sense that the input node data should be accessible since they provide input data for the parent node. You can ignore my initial finding.

For parallel processing, I am a little hesitating, because the goal is to reduce the CPU cost on HVs (to save CPU for real workloads). The processing engine should be non-blocking, so if we need parallel processing in the engine, it means we are requesting too much CPU on the HV. I hope we don't need parallel processing for flow computing.

That's a good point.

> All that being said, I would be happy to see a change like this go in as-is (pending more in-depth code review, of course) if the data encapsulation work would creep the scope out too much for the initial changeset.
 > Mark!
 > On 02/20/2018 01:04 PM, Han Zhou wrote:
>> ovn-controller currently recomputes everything when there are any changes
 >> of input, which leads to high CPU usages and slow in end-to-end flow
>> enforcement in response to changes. It even wastes CPU to recompute flows
 >> for unrelated inputs such as pinctrl events.
 >> This patch series implements incremental processing in ovn-controller to
>> solve above problems. There has been a similar attempt of solve the problem
 >> earlier but was reverted (see commit: 926c34fd). This patch series takes
 >> a different approach with an incremental processing engine, to make the
>> dependencies clear and easier to maintain. The engine is a DAG representing >> dependencies between different nodes. Each node maintains its own data, which >> depends on its inputs and the data can also be inputs of other nodes. Each >> node implements a method to recompute its data based on all the inputs, but >> also implements methods to handle changes of different inputs incrementally. >> The engine will be responsible to try incremental processing for each node >> based on the dependencies or fallback to recompute when changes cannot be
 >> handled incrementally.
 >> This patch series can incrementally process the most common changes:
>> logical flows and port bindings from OVNSB. It can be expanded further for
 >> more fine grained incremental processing gradually.
 >> With the patch series, the CPU time of ovn-controller in ovn-scale-test
 >> for 500 lports creating and binding on 50 HVs decreased 90%.
>> This is RFC version to get feedback to see if there is any major issue of >> this approach, before refining it future for formal review. There are still
 >> two test cases failed and debugging ongoing.
 >> Han Zhou (8):
 >>    ovn-controller: Incremental processing engine
 >>    ovn-controller: Track OVSDB changes
 >>    ovn-controller: Initial use of incremental engine in main
 >>    ovn-controller: Split SB inputs as separate incremental engine nodes
 >>    ovn-controller: split ovs_idl inputs in incremental engine
 >>    ovn-controller: Incremental logical flow processing
 >>    ovn-controller: runtime_data change handler for SB port-binding
>>    ovn-controller: port-binding incremental processing for physical flows
 >>   include/ovn/actions.h           |   3 +
 >>   ovn/controller/bfd.c            |   4 +-
 >>   ovn/controller/binding.c        | 101 +++++++-
 >>   ovn/controller/binding.h        |   6 +
 >>   ovn/controller/encaps.c         |  12 +-
 >>   ovn/controller/lflow.c          | 104 ++++++--
 >>   ovn/controller/lflow.h          |  10 +-
 >>   ovn/controller/ofctrl.c         | 226 ++++++++++++-----
 >>   ovn/controller/ofctrl.h         |  16 +-
>>   ovn/controller/ovn-controller.c | 546 +++++++++++++++++++++++++++++++---------
 >>   ovn/controller/ovn-controller.h |   5 +
 >>   ovn/controller/physical.c       | 140 +++++++----
 >>   ovn/controller/physical.h       |   8 +-
 >>   ovn/lib/actions.c               |   6 +-
 >>   ovn/lib/automake.mk <http://automake.mk>             |   4 +-
 >>   ovn/lib/extend-table.c          |  31 ++-
 >>   ovn/lib/extend-table.h          |   9 +-
 >>   ovn/lib/inc-proc-eng.c          |  97 +++++++
 >>   ovn/lib/inc-proc-eng.h          | 118 +++++++++
 >>   19 files changed, 1143 insertions(+), 303 deletions(-)
 >>   create mode 100644 ovn/lib/inc-proc-eng.c
 >>   create mode 100644 ovn/lib/inc-proc-eng.h

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