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.


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

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