Wladimir J. van der Laan 43f3ada27b Merge #19866: eBPF Linux tracepoints ...

22eb7930a6 tracing: add tracing framework (William Casarin)
933ab8a720 build: detect sys/sdt.h for eBPF tracing (William Casarin)

Pull request description:

  Instead of writing ad-hoc logging everywhere (eg: #19509), we can take advantage of linux user static defined traces, aka. USDTs ( not the stablecoin 😅 )

  The linux kernel can hook into these tracepoints at runtime, but otherwise they have little to no performance impact. Traces can pass data which can be printed externally via tools such as bpftrace. For example, here's one that prints incoming and outgoing network messages:

  # Examples

  ## Network Messages

  ```
  #!/usr/bin/env bpftrace

  BEGIN
  {
    printf("bitcoin net msgs\n");
    @start = nsecs;
  }

  usdt:./src/bitcoind:net:push_message
  {
    $ip = str(arg0);
    $peer_id = (int64)arg1;
    $command = str(arg2);
    $data_len = arg3;
    $data = buf(arg3,arg4);
    $t = (nsecs - @start) / 100000;

    printf("%zu outbound %s %s %zu %d %r\n", $t, $command, $ip, $peer_id, $data_len, $data);

    @outbound[$command]++;
  }

  usdt:./src/bitcoind:net:process_message
  {
    $ip = str(arg0);
    $peer_id = (int64)arg1;
    $command = str(arg2);
    $data_len = arg3;
    $data = buf(arg3,arg4);
    $t = (nsecs - @start) / 100000;

    printf("%zu inbound %s %s %zu %d %r\n", $t, $command, $ip, $peer_id, $data_len, $data);

    @inbound[$ip, $command]++;
  }

  ```

      $ sudo bpftrace netmsg.bt

  output: https://jb55.com/s/b11312484b601fb3.txt

  if you look at the bottom of the output you can see a histogram of all the messages grouped by message type and IP. nice!

  ## IBD Benchmarking

  ```
  #!/usr/bin/env bpftrace
  BEGIN
  {
    printf("IBD to 500,000 bench\n");
  }

  usdt:./src/bitcoind:CChainState:ConnectBlock
  {
    $height = (uint32)arg0;

    if ($height == 1) {
      printf("block 1 found, starting benchmark\n");
      @start = nsecs;
    }

    if ($height >= 500000) {
      @end = nsecs;
      @duration = @end - @start;
      exit();
    }
  }

  END {
    printf("duration %d ms\n", @duration / 1000000)
  }
  ```
  This one hooks into ConnectBlock and prints the IBD time to height 500,000 starting from the first call to ConnectBlock

  Userspace static tracepoints give lots of flexibility without invasive logging code. It's also more flexible than ad-hoc logging code, allowing you to instrument many different aspects of the system without having to enable per-subsystem logging.

  Other ideas: tracepoints for lock contention, threads, what else?

  Let me know what ya'll think and if this is worth adding to bitcoin.

  ## TODO

  - [ ] docs?
  - [x] Integrate systemtap-std-dev/libsystemtap into build (provides the <sys/sdt.h> header)
  - [x] ~dtrace macos support? (is this still a thing?)~ going to focus on linux for now

ACKs for top commit:
  laanwj:
    Tested ACK 22eb7930a6
  0xB10C:
    Tested ACK 22eb7930a6

Tree-SHA512: 69242242112b679c8a12a22b3bc50252c305894fb3055ae6e13d5f56221d858e58af1d698af55e23b69bdb7abedb5565ac6b45fa5144087b77a17acd04646a75

2021-01-18 22:09:05 +01:00

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