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OpenCyphal / pycyphal

Python implementation of the Cyphal protocol stack.
https://pycyphal.readthedocs.io/
MIT License
123 stars 106 forks source link

use much faster crcmod library for crc #30

Closed jschall closed 6 years ago

pavel-kirienko commented 6 years ago

I have a better proposition. Consider the result of profiling you shared yesterday:

24527    0.108    0.000    7.077    0.000 /usr/local/lib/python3.5/dist-packages/uavcan/node.py:295(_recv_frame)
24527    0.224    0.000    6.634    0.000 /usr/local/lib/python3.5/dist-packages/uavcan/transport.py:752(from_frames)
24527    0.064    0.000    4.885    0.000 /usr/local/lib/python3.5/dist-packages/uavcan/dsdl/parser.py:304(get_data_type_signature)
24527    0.039    0.000    4.780    0.000 /usr/local/lib/python3.5/dist-packages/uavcan/dsdl/parser.py:293(get_dsdl_signature)
24527    0.036    0.000    4.352    0.000 /usr/local/lib/python3.5/dist-packages/uavcan/dsdl/signature.py:61(compute_signature)
24527    4.294    0.000    4.298    0.000 /usr/local/lib/python3.5/dist-packages/uavcan/dsdl/signature.py:39(add)

We can eliminate CRC computation completely, no extra dependencies necessary. The result of the method get_dsdl_signature is dependent only on the definition of its data type, which can't change while the program is running. So I propose to keep the current CRC computation algorithm unchanged, but cache the output of get_dsdl_signature; alternatively, we can compute the signature when the object is constructed and keep the result; in that case, get_dsdl_signature will just return the precomputed result.

A fair bit of computation is happening also here in get_data_type_signature: https://github.com/UAVCAN/pyuavcan/blob/0fd4122fe6e128aabd00d5ca88aba5cc82518c9c/uavcan/dsdl/parser.py#L304-L318 We could apply caching or precomputation here as well.

pavel-kirienko commented 6 years ago

Closing in favor of https://github.com/UAVCAN/pyuavcan/pull/31