[ovs-dev] [RFC 0/8] ovn-controller Incremental Processing

[Mark Michelson]

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. 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).

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.

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             |   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
>