SRT: Performance is low caused by srs_assert

[winlinvip]

Note: Please read FAQ before file an issue, see #2716

Description

Please description your issue here

1. SRS Version: 6.0.38

2. SRS Config: conf/srt.conf

Replay

Please describe how to replay the bug?

Step 1: Start SRS

./objs/srs -c conf/srt.conf 

Step 2: Publish by FFmpeg

ffmpeg -stream_loop -1 -re -i bbb.h264.mp4 -c copy -pes_payload_size 0 -f mpegts 'srt://localhost:10080?streamid=#!::r=live/livestream,m=publish'

Note: The bitrate must be large enough, 30Mbps+

Step 3: top

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                                                                                                     
 173532 winlin    20   0   20.0t 403352  10844 S  52.0  10.1   0:10.91 ./objs/srs -c console.conf

sudo perf top -p $(pidof srs)

Samples: 5K of event 'cpu-clock:pppH', 4000 Hz, Event count (approx.): 1269558516 lost: 0/0 drop: 0/0
Overhead  Shared Object        Symbol
  32.08%  srs                  [.] SrsCplxError::srs_assert
  12.97%  srs                  [.] SrsBuffer::skip
   5.81%  srs                  [.] SrsBuffer::empty
   5.27%  srs                  [.] srs_avc_startswith_annexb
   3.86%  srs                  [.] SrsBuffer::require
   2.56%  [kernel]             [k] finish_task_switch
   2.21%  srs                  [.] SrsBuffer::data
   2.12%  srs                  [.] SrsBuffer::pos

Expect

If disable the SRT to RTMP, CPU usage is low, about 5%.

[winlinvip]

When we finish the refactor of SRT server structure for #3251, we will start this performance improvement.