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tracing: drop block_connected hash.toString() arg

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The tracepoint `validation:block_connected` was introduced in #22006.
The first argument was the hash of the connected block as a pointer
to a C-like String. The last argument passed the hash of the
connected block as a pointer to 32 bytes. The hash was only passed as
string to allow `bpftrace` scripts to print the hash. It was
(incorrectly) assumed that `bpftrace` cannot hex-format and print the
block hash given only the hash as bytes.

The block hash can be printed in `bpftrace` by calling
`printf("%02x")` for each byte of the hash in an `unroll () {...}`.
By starting from the last byte of the hash, it can be printed in
big-endian (the block-explorer format).

```C
  $p = $hash + 31;
  unroll(32) {
      $b = *(uint8*)$p;
      printf("%02x", $b);
      $p -= 1;
  }
```

See also: https://github.com/bitcoin/bitcoin/pull/22902#discussion_r705176691

This is a breaking change to the block_connected tracepoint API, however
this tracepoint has not yet been included in a release.
This commit is contained in:
0xb10c
2021-10-18 13:19:13 +02:00
parent 3bf40d06a2
commit 53c9fa9e62
4 changed files with 19 additions and 26 deletions
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7
contrib/tracing/README.md
View File

@ -176,17 +176,12 @@ third acts as a duration threshold in milliseconds. When the `ConnectBlock()`
function takes longer than the threshold, information about the block, is
printed. For more details, see the header comment in the script.
By default, `bpftrace` limits strings to 64 bytes due to the limited stack size
in the kernel VM. Block hashes as zero-terminated hex strings are 65 bytes which
exceed the string limit. The string size limit can be set to 65 bytes with the
environment variable `BPFTRACE_STRLEN`.
The following command can be used to benchmark, for example, `ConnectBlock()`
between height 20000 and 38000 on SigNet while logging all blocks that take
longer than 25ms to connect.
```
$ BPFTRACE_STRLEN=65 bpftrace contrib/tracing/connectblock_benchmark.bt 20000 38000 25
$ bpftrace contrib/tracing/connectblock_benchmark.bt 20000 38000 25
```
In a different terminal, starting Bitcoin Core in SigNet mode and with

22
contrib/tracing/connectblock_benchmark.bt
View File

@ -4,11 +4,8 @@
USAGE:
BPFTRACE_STRLEN=65 bpftrace contrib/tracing/connectblock_benchmark.bt <start height> <end height> <logging threshold in ms>
bpftrace contrib/tracing/connectblock_benchmark.bt <start height> <end height> <logging threshold in ms>
- The environment variable BPFTRACE_STRLEN needs to be set to 65 chars as
strings are limited to 64 chars by default. Hex strings with Bitcoin block
hashes are 64 hex chars + 1 null-termination char.
- <start height> sets the height at which the benchmark should start. Setting
the start height to 0 starts the benchmark immediately, even before the
first block is connected.
@ -23,7 +20,7 @@
EXAMPLES:
BPFTRACE_STRLEN=65 bpftrace contrib/tracing/connectblock_benchmark.bt 300000 680000 1000
bpftrace contrib/tracing/connectblock_benchmark.bt 300000 680000 1000
When run together 'bitcoind -reindex', this benchmarks the time it takes to
connect the blocks between height 300.000 and 680.000 (inclusive) and prints
@ -31,7 +28,7 @@
histogram with block connection times when the benchmark is finished.
BPFTRACE_STRLEN=65 bpftrace contrib/tracing/connectblock_benchmark.bt 0 0 500
bpftrace contrib/tracing/connectblock_benchmark.bt 0 0 500
When running together 'bitcoind', all newly connected blocks that
take longer than 500ms to connect are logged. A histogram with block
@ -107,14 +104,23 @@ usdt:./src/bitcoind:validation:block_connected /arg1 >= $1 && (arg1 <= $2 || $2
*/
usdt:./src/bitcoind:validation:block_connected / (uint64) arg5 / 1000> $3 /
{
$hash_str = str(arg0);
$hash = arg0;
$height = (int32) arg1;
$transactions = (uint64) arg2;
$inputs = (int32) arg3;
$sigops = (int64) arg4;
$duration = (int64) arg5;
printf("Block %d (%s) %4d tx %5d ins %5d sigops took %4d ms\n", $height, $hash_str, $transactions, $inputs, $sigops, (uint64) $duration / 1000);
printf("Block %d (", $height);
/* Prints each byte of the block hash as hex in big-endian (the block-explorer format) */
$p = $hash + 31;
unroll(32) {
$b = *(uint8*)$p;
printf("%02x", $b);
$p -= 1;
}
printf(") %4d tx %5d ins %5d sigops took %4d ms\n", $transactions, $inputs, $sigops, (uint64) $duration / 1000);
}