performance: more cost on CPU when upgrading to v0.13.0

[LykxSassinator]

Problem Descriptions

When trying to upgrade the grpcio version from v0.10.3 to the latest version v0.13.0 in TiKV, it seems that it costs more CPU compared to the previous version v0.10.3.

• Related upgrading pr is: grpc-io: upgrade to latest version - v0.13.0. tikv#16165
• Testing results can be reviewed at comment.

And according to profiling flame-graph, the grpcio module might introduce more cost on CompletionQueue::next().

• Master(with v0.10.3 version)
  

• Upgraded pr(with 0.13.0 version)
  

Source profiling files can be reviewed in: comparison.zip

[BusyJay]

Also check the release note in https://github.com/tikv/grpc-rs/releases/tag/v0.12.0.