Handles multiple chunks in inter-thread communication

teip degrades the performance rapidly if is has large number of small chunks.

$ yes | tr -d \\n | fold -w 1024 | TEIP_HIGHLIGHT="<{}>" teip -og . | head -n 1
<y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y><y>...

$ yes | tr -d \\n | fold -w 1024 | TEIP_HIGHLIGHT="<{}>" teip -og . | pv >/dev/null
.0MiB 0:00:05 [3.59MiB/s] [              <=>                                                                                                                                     ]
$ yes | tr -d \\n | fold -w 1024 | TEIP_HIGHLIGHT="<{}>" teip -og '.{64}' | pv >/dev/null
30MiB 0:00:04 [31.7MiB/s] [           <=>                                                                                                                                        ]

I believe that this performance degration is caused by the large mount of inter-thread communication. Actually, futex occupies large ratio of execution time.

$ yes | tr -d \\n | fold -w 1024 | head -n 1024 | TEIP_HIGHLIGHT="<{}>" strace -cf teip -og .
︙
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 92.52    0.582339           7     85927     34598 futex
  5.85    0.036801          36      1026           write
  0.67    0.004226           9       485           sched_yield
  0.49    0.003090          24       130           read
  0.35    0.002197           9       248           brk
  0.06    0.000409         102         4           mmap
  0.01    0.000083          10         8           rt_sigprocmask
  0.01    0.000055          11         5           rt_sigaction
  0.01    0.000047           8         6           sigaltstack
  0.01    0.000039          13         3           munmap
  0.00    0.000028           9         3           mprotect
  0.00    0.000020          20         1           clone
  0.00    0.000016          16         1           poll
  0.00    0.000014          14         1           getrandom
  0.00    0.000013          13         1           ioctl
  0.00    0.000013          13         1           arch_prctl
  0.00    0.000010          10         1           set_tid_address
  0.00    0.000000           0         1           execve
------ ----------- ----------- --------- --------- ----------------
100.00    0.629400                 87852     34598 total

To mitigate the issue, it is good idea to reduce the number of futex calls. Currently, the PipeIntercepter sends single chunk by tx.send for each time.

https://github.com/greymd/teip/blob/v2.2.0/src/pipeintercepter.rs#L23-L53 https://github.com/greymd/teip/blob/v2.2.0/src/pipeintercepter.rs#L235

This part can be improved more. If PipeIntercepter can bufferes chunks and sends it to other thread, number of futex will be reduced and performance improves rapidly under such the particular situation likea above.

greymd / teip

Handles multiple chunks in inter-thread communication #55