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merge-script 19f277711e
Merge bitcoin/bitcoin#26593: tracing: Only prepare tracepoint arguments when actually tracing 
0de3e96e33 tracing: use bitcoind pid in bcc tracing examples (0xb10c)
411c6cfc6c tracing: only prepare tracepoint args if attached (0xb10c)
d524c1ec06 tracing: dedup TRACE macros & rename to TRACEPOINT (0xb10c)

Pull request description:

  Currently, if the tracepoints are compiled (e.g. in depends and release builds), we always prepare the tracepoint arguments regardless of the tracepoints being used or not. We made sure that the argument preparation is as cheap as possible, but we can almost completely eliminate any overhead for users not interested in the tracepoints (the vast majority), by gating the tracepoint argument preparation with an `if(something is attached to this tracepoint)`. To achieve this, we use the optional semaphore feature provided by SystemTap.

  The first commit simplifies and deduplicates our tracepoint macros from 13 TRACEx macros to a single TRACEPOINT macro. This makes them easier to use and also avoids more duplicate macro definitions in the second commit.

  The Linux tracing tools I'm aware of (bcc, bpftrace, libbpf, and systemtap) all support the semaphore gating feature. Thus, all existing tracepoints and their argument preparation is gated in the second commit. For details, please refer to the commit messages and the updated documentation in `doc/tracing.md`.

  Also adding unit tests that include all tracepoint macros to make sure there are no compiler problems with them (e.g. some varadiac extension not supported).

  Reviewers might want to check:
  - Do the tracepoints still work for you? Do the examples in `contrib/tracing/` run on your system (as bpftrace frequently breaks on every new version, please test master too if it should't work for you)? Do the CI interface tests still pass?
  - Is the new documentation clear?
  - The `TRACEPOINT_SEMAPHORE(event, context)` macros places global variables in our global namespace. Is this something we strictly want to avoid or maybe move to all `TRACEPOINT_SEMAPHORE`s to a separate .cpp file or even namespace? I like having the `TRACEPOINT_SEMAPHORE()` in same file as the `TRACEPOINT()`, but open for suggestion on alternative approaches.
  - Are newly added tracepoints in the unit tests visible when using `readelf -n build/src/test/test_bitcoin`? You can run the new unit tests with `./build/src/test/test_bitcoin --run_test=util_trace_tests* --log_level=all`.
  <details><summary>Two of the added unit tests demonstrate that we are only processing the tracepoint arguments when attached by having a test-failure condition in the tracepoint argument preparation. The following bpftrace script can be used to demonstrate that the tests do indeed fail when attached to the tracepoints.</summary>

  `fail_tests.bt`:

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

  usdt:./build/src/test/test_bitcoin:test:check_if_attached {
    printf("the 'check_if_attached' test should have failed\n");
  }

  usdt:./build/src/test/test_bitcoin:test:expensive_section {
    printf("the 'expensive_section' test should have failed\n");
  }
  ```

  Run the unit tests with `./build/src/test/test_bitcoin` and start `bpftrace fail_tests.bt -p $(pidof test_bitcoin)` in a separate terminal. The unit tests should fail with:

  ```
  Running 594 test cases...
  test/util_trace_tests.cpp(31): error: in "util_trace_tests/test_tracepoint_check_if_attached": check false has failed
  test/util_trace_tests.cpp(51): error: in "util_trace_tests/test_tracepoint_manual_tracepoint_active_check": check false has failed

  *** 2 failures are detected in the test module "Bitcoin Core Test Suite"
  ```

  </details>

  These links might provide more contextual information for reviewers:
  - [How SystemTap Userspace Probes Work by eklitzke](https://eklitzke.org/how-sytemtap-userspace-probes-work) (actually an example on Bitcoin Core; mentions that with semaphores "the overhead for an untraced process is effectively zero.")
  - [libbpf comment on USDT semaphore handling](1596a09b5d/src/usdt.c (L83-L92)) (can recommend the whole comment for background on how the tracepoints and tracing tools work together)
  - https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation#Semaphore_Handling

ACKs for top commit:
  willcl-ark:
    utACK 0de3e96e33
  laanwj:
    re-ACK 0de3e96e33
  jb55:
    utACK 0de3e96e33
  vasild:
    ACK 0de3e96e33

Tree-SHA512: 0e5e0dc5e0353beaf5c446e4be03d447e64228b1be71ee9972fde1d6fac3fac71a9d73c6ce4fa68975f87db2b2bf6eee2009921a2a145e24d83a475d007a559b
2024-11-11 10:33:28 +00:00
..
asmap Compare ASMaps with respect to specific addresses 2024-06-27 16:35:15 +02:00
completions testnet: Introduce Testnet4 2024-08-06 01:38:10 +02:00
debian doc: upgrade Bitcoin Core license to 2024 2024-01-10 16:29:01 -06:00
devtools build: Bump minimum supported macOS to 13.0 2024-10-15 10:18:48 +01:00
guix build: Unify -logsourcelocations format 2024-11-04 11:30:43 +00:00
init
linearize contrib: support reading XORed blocks in linearize-data.py script 2024-08-07 23:53:39 +02:00
macdeploy Merge bitcoin/bitcoin#30287: macOS: rewrite some docs & swap mmacosx-version-min for mmacos-version-min 2024-06-18 10:55:46 +01:00
message-capture test: use built-in collection types for type hints (Python 3.9 / PEP 585) 2023-10-25 01:10:21 +02:00
qos
seeds contrib: Update asmap link in seeds readme 2024-09-26 15:54:01 +02:00
shell
signet doc: update signet documentation related to build directories 2024-09-28 20:53:21 +02:00
testgen
tracing tracing: use bitcoind pid in bcc tracing examples 2024-10-28 14:27:54 +01:00
verify-binaries contrib: Fixup verify-binaries OS platform parsing 2024-06-25 11:32:56 -05:00
verify-commits
windeploy windeploy: Renew certificate 2024-05-21 23:19:51 -04:00
zmq
filter-lcov.py
README.md
valgrind.supp doc: Prepend 'build/' to binary paths under 'src/' in docs 2024-08-29 15:23:12 +02:00

README.md

Repository Tools

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Linearize

Construct a linear, no-fork, best version of the blockchain.

Qos

A Linux bash script that will set up traffic control (tc) to limit the outgoing bandwidth for connections to the Bitcoin network. This means one can have an always-on bitcoind instance running, and another local bitcoind/bitcoin-qt instance which connects to this node and receives blocks from it.

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Utility to generate the pnSeed[] array that is compiled into the client.

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