Re: [PATCH v1 0/4] [RFC] Testpmd RPC API

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, Apr 11, 2022 at 11:19 PM Owen Hilyard <ohilyard@iol.unh.edu> wrote:
>>
>> scheme is probably over-engineered
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> I tried my hardest to keep this as simple as possible. The requirements imposed by DTS being a distributed system in Python restricted what I could do a lot. Needing to be compatible with DPDK's license also got rid of a lot of options. Binding generators are made for simple projects, and DPDK is not a simple project. There were some other options related to choice in the RPC framework, but very few RPC protocols seem to work well with C and be usable from Python, which is why I ended up using C++ with gRPC. Most of the code in api_impl.cc is taken from /app/test-acl/main.c, and the new part is mostly the C++ class at the bottom. Overall, this proposal comes out to ~100 lines of new C++, 9 lines of C, 12 lines of gRPC Protobuf and 100 lines of Meson. gRPC may be able to do a lot more than I need it to for the proof of concept, but many of the features that are not used, like bi-directional streaming, become very useful in writing more complicated tests. Overall, this solution is probably more capable than we need it to be, but I think that those extra capabilities don't come at a very large cost.


Now it is clear, I was carried away with the POC test application and
I was not knowing existing DTS tests are based on python

Is below a fair summary?

1) DPDK has interactive test cases and no interactive test cases.

For The interactive test case like testpmd, I agree that we can enable
RPC service via gRPC server in C++ as  and client in Python, and
something along the lines of exposing the existing test-pmd command
line function as service
to avoid command line parsing and reuse the existing python test suite.

If so, I think, gRPC service would be along with existing testpmd
functions, like start_packet_forwarding(). Also, We don't need to
rewrite the existing testpmd,
Instead, RPC service, we can add in existing app/test-pmd/ and hook to
existing core testpmd functions to bypass the command-line parsing in
C and control from python client as needed as service.

Also, I agree that pulling in gRPC C++ server boilerplate and hooking
to C functions is a good idea as it is the best C-based RPC scheme
available today.

2)I think, DPDK has only one interactive test case which is testpmd,
Remaining test cases are non-interactive, non-interactive test cases
can simply run over ssh with passwordless login. Right?
Do we need gRPC for that? Will the following scheme suffice? If not,
How you are planning to do noninteractive test cases?
i.e
a)Copy test to target
b) result=`ssh username@IP /path/to/testapp/in/target`

I think, key should be leveraging existing test cases as much as
possible and make easy for developers to add new test cases.


>>
>> Now that, Test code is also part of DPDK.
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> DTS is pure python. I tried to use FFI to call directly into DPDK from Python and then use xmlrpc from the python standard library. As mentioned in the writeup, I couldn't find a binding generator that would properly handle DPDK's allocators, which made it so that anything passed to DPDK using python was allocated using the system malloc. I don't think it is wise to attempt to programmatically re-write the generated code to allow for custom allocators. The original reason for needing to have DTS and DPDK in the same repository was so that tests could be committed and run alongside the feature patch.
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>> Interactive - Testpmd one, I believe, Feeding stdin programmatically would suffice to test all the combinations.
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> One of the issues this is trying to address is that human-readable strings are a poor way to pass complex information between two programs. DTS is a distributed system, and it can have up to 3 physical servers involved in any given test. This means that it's not stdin via a pipe, it's an entire SSH session. This adds a noticeable amount of overhead when trying to send and verify the result of sending 1,000+ packets, since the lack of structured output means each packet must be checked before the next can be sent. This might be solvable by adding a structured output mode to testpmd, but that would involve committing to writing output twice for every function in testpmd forever.
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>> We need to add all test cases in this model and we need to maintain two sets of programs.(Traditional tests and gRPC model-based tests).
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> Assuming by traditional tests you mean the unit tests run by Meson, I would argue that we are already maintaining 2 kinds of tests. The unit tests, and the python-based DTS tests. My intention is to create a thin wrapper around DPDK that would be exposed via gRPC, like you see here, and use that as midware. Then, we would have two front-ends. Testpmd, which takes text and then calls midware as it does now, and the gRPC frontend, which parses messages from the RPC server and runs the midware. This would enable testpmd to still be used to sanity check a DPDK installation, but we would not need to continually expand Testpmd. The primary issue is that, right now, anything not included in Testpmd is not really testable by DTS. This includes portions of the RTE Flow API, which was part of my reason for proposing this. The RTE Flow API would, in my estimation, if fully implemented into Testpmd, probably add at least another 10,000 lines of code. As mentioned in my proposal, Testpmd already does more parsing and lexing than it does interaction with DPDK by line count. Also, since I am proposing making this a separate application, we would be able to gradually migrate the tests inside of DTS. This would have no effect on anything except for Testpmd, the new application and the addition of a flag to toggle the use of a C++ compiler.
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> I'm not sure exactly what you mean by gRPC model-based tests. gRPC uses classes to model services, but for this usecase we are essentially using it to transfer function arguments across the internet and then pass the return value back. Any RPC framework would function similarly if I ignored the restrictions of which languages to use, and the choice is not important to how tests are conducted. Put another way, how you write a test for DTS will not change much if you are using this or testpmd, it's just how you transfer data and get it back that I want to change.