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19f277711e
0de3e96e333090548a43e5e870c4cb8941d6baf1 tracing: use bitcoind pid in bcc tracing examples (0xb10c)
411c6cfc6c2e488e407f057b646730e63806ed8a tracing: only prepare tracepoint args if attached (0xb10c)
d524c1ec06643208c189089089e84f6e1cd0abad 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 0de3e96e333090548a43e5e870c4cb8941d6baf1
laanwj:
re-ACK 0de3e96e333090548a43e5e870c4cb8941d6baf1
jb55:
utACK 0de3e96e333090548a43e5e870c4cb8941d6baf1
vasild:
ACK 0de3e96e333090548a43e5e870c4cb8941d6baf1
Tree-SHA512: 0e5e0dc5e0353beaf5c446e4be03d447e64228b1be71ee9972fde1d6fac3fac71a9d73c6ce4fa68975f87db2b2bf6eee2009921a2a145e24d83a475d007a559b
Bitcoin Core
Setup
Bitcoin Core is the original Bitcoin client and it builds the backbone of the network. It downloads and, by default, stores the entire history of Bitcoin transactions, which requires several hundred gigabytes or more of disk space. Depending on the speed of your computer and network connection, the synchronization process can take anywhere from a few hours to several days or more.
To download Bitcoin Core, visit bitcoincore.org.
Running
The following are some helpful notes on how to run Bitcoin Core on your native platform.
Unix
Unpack the files into a directory and run:
bin/bitcoin-qt(GUI) orbin/bitcoind(headless)
Windows
Unpack the files into a directory, and then run bitcoin-qt.exe.
macOS
Drag Bitcoin Core to your applications folder, and then run Bitcoin Core.
Need Help?
- See the documentation at the Bitcoin Wiki for help and more information.
- Ask for help on Bitcoin StackExchange.
- Ask for help on #bitcoin on Libera Chat. If you don't have an IRC client, you can use web.libera.chat.
- Ask for help on the BitcoinTalk forums, in the Technical Support board.
Building
The following are developer notes on how to build Bitcoin Core on your native platform. They are not complete guides, but include notes on the necessary libraries, compile flags, etc.
- Dependencies
- macOS Build Notes
- Unix Build Notes
- Windows Build Notes
- FreeBSD Build Notes
- OpenBSD Build Notes
- NetBSD Build Notes
Development
The Bitcoin repo's root README contains relevant information on the development process and automated testing.
- Developer Notes
- Productivity Notes
- Release Process
- Source Code Documentation (External Link)
- Translation Process
- Translation Strings Policy
- JSON-RPC Interface
- Unauthenticated REST Interface
- BIPS
- Dnsseed Policy
- Benchmarking
- Internal Design Docs
Resources
- Discuss on the BitcoinTalk forums, in the Development & Technical Discussion board.
- Discuss project-specific development on #bitcoin-core-dev on Libera Chat. If you don't have an IRC client, you can use web.libera.chat.
Miscellaneous
- Assets Attribution
- bitcoin.conf Configuration File
- CJDNS Support
- Files
- Fuzz-testing
- I2P Support
- Init Scripts (systemd/upstart/openrc)
- Managing Wallets
- Multisig Tutorial
- Offline Signing Tutorial
- P2P bad ports definition and list
- PSBT support
- Reduce Memory
- Reduce Traffic
- Tor Support
- Transaction Relay Policy
- ZMQ
License
Distributed under the MIT software license.