Reducing memory allocations in read RTCP methods

[tyohan]

I'm profiling Inlive SFU to see how we can reduce the CPU usage and found out the ReadRTCP memory is keep allocating new memory for each RTCP packet and put a high pressure on the GC.

So I create a benchmark test on unmarshal method and to see if using sync.Pool and some other improvement can make a significant impact and the result comes with this below:

Before using sync.Pool

BenchmarkUnmarshal-8   	 2621134	       414.3 ns/op	     584 B/op	      16 allocs/op

After using sync.Pool

BenchmarkUnmarshal-8   	 3275593	       356.6 ns/op	     384 B/op	      10 allocs/op

[Sean-Der]

Sorry I missed this @tyohan !

I added you to the org so you can create branches/dev easier.

[codecov]

Codecov Report

Attention: Patch coverage is 88.63636% with 10 lines in your changes missing coverage. Please review.

Project coverage is 79.05%. Comparing base (26bcda5) to head (d76d213).

Files with missing lines	Patch %	Lines
packet.go	82.50%	7 Missing ⚠️
compound_packet.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #185      +/-   ##
==========================================
+ Coverage   78.50%   79.05%   +0.55%     
==========================================
  Files          22       22              
  Lines        2005     2072      +67     
==========================================
+ Hits         1574     1638      +64     
- Misses        336      339       +3     
  Partials       95       95              

Flag	Coverage Δ
go	79.05% <88.63%> (+0.55%)	⬆️
wasm	79.05% <88.63%> (+0.55%)	⬆️

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[Sean-Der]

What happens if users don’t call Release

I am 100% in support of performance changes, as long as they don’t impact existing users!

[tyohan]

Thank you for adding me to the org @Sean-Der

So far from my understanding of sync.Pool, without release the packet or we don't put it back to the pool it will treated just like the current implementation. The memory will be release once there is no reference to it. But if it put back to the pool, it will reuse once there is a request to the new packet.

I still trying to figure out what the best way to implement this without impacting the Pion API. I'll request more feedback from Pion slack channel.