Merge bitcoin/bitcoin#22902: tracing: utxocache tracepoints

2bc51c5 [tracing] tracepoints to utxocache add, spent and uncache (Arnab Sen)
a26e8ee [tracing] tracepoint for utxocache flushes (Arnab Sen)

Pull request description:

  This PR adds some of the UTXO set cache tracepoints proposed in bitcoin/bitcoin#20981 (comment). The first tracepoints were added in bitcoin#22006.

  tracepoint | description
  -- | --
  `utxocache:flush` | Is called after the caches and indexes are flushed
  `utxocache:add` | when a new coin is added to the UTXO cache
  `utxocache:spent` | when a coin is spent
  `utxocache:uncache` | when coin is removed from the UTXO cache

  The tracepoints are further documented in `docs/tracing.md` and the usage is shown via the two newly added example scripts in `contrib/tracing/`.

ACKs for top commit:
  laanwj:
    Code and documentation review ACK 2bc51c5

Tree-SHA512: d6b4f435d3260de4c48b36956f9311f65ab3b52cd03b1e0a4ba9cf47a774d8c4b31878e222b11e0ba5d233a68f7567f8a367b12a6392f688c10c11529341e837

Author: laanwj

contrib/tracing/README.md

@@ -234,3 +234,62 @@ Histogram of block connection times in milliseconds (ms).
 [16, 32)               9 |                                                    |
 [32, 64)               4 |                                                    |
 ```
+
+### log_utxocache_flush.py
+
+A BCC Python script to log the cache and index flushes. Based on the
+`utxocache:flush` tracepoint.
+
+```bash
+$ python3 contrib/tracing/log_utxocache_flush.py ./src/bitcoind
+```
+
+```
+Logging utxocache flushes. Ctrl-C to end...
+Duration (µs)   Mode       Coins Count     Memory Usage    Prune    Full Flush
+0               PERIODIC   28484           3929.87 kB      False    False
+1               PERIODIC   28485           3930.00 kB      False    False
+0               PERIODIC   28489           3930.51 kB      False    False
+1               PERIODIC   28490           3930.64 kB      False    False
+0               PERIODIC   28491           3930.77 kB      False    False
+0               PERIODIC   28491           3930.77 kB      False    False
+0               PERIODIC   28496           3931.41 kB      False    False
+1               PERIODIC   28496           3931.41 kB      False    False
+0               PERIODIC   28497           3931.54 kB      False    False
+1               PERIODIC   28497           3931.54 kB      False    False
+1               PERIODIC   28499           3931.79 kB      False    False
+.
+.
+.
+53788           ALWAYS     30076           4136.27 kB      False    False
+7463            ALWAYS     0               245.84 kB       False    False
+```
+
+### log_utxos.bt
+
+A `bpftrace` script to log information about the coins that are added, spent, or
+uncached from the UTXO set. Based on the `utxocache:add`, `utxocache:spend` and
+`utxocache:uncache` tracepoints.
+
+```bash
+$ bpftrace contrib/tracing/log_utxos.bt
+```
+
+It should produce an output similar to the following.
+
+```bash
+Attaching 4 probes...
+OP      Outpoint                                                                           Value  Height Coinbase
+Added   6ba9ad857e1ef2eb2a2c94f06813c414c7ab273e3d6bd7ad64e000315a887e7c:1                 10000 2094512 No
+Spent   fa7dc4db56637a151f6649d8f26732956d1c5424c82aae400a83d02b2cc2c87b:0             182264897 2094512 No
+Added   eeb2f099b1af6a2a12e6ddd2eeb16fc5968582241d7f08ba202d28b60ac264c7:0                 10000 2094512 No
+Added   eeb2f099b1af6a2a12e6ddd2eeb16fc5968582241d7f08ba202d28b60ac264c7:1             182254756 2094512 No
+Added   a0c7f4ec9cccef2d89672a624a4e6c8237a17572efdd4679eea9e9ee70d2db04:0              10072679 2094513 Yes
+Spent   25e0df5cc1aeb1b78e6056bf403e5e8b7e41f138060ca0a50a50134df0549a5e:2                   540 2094508 No
+Spent   42f383c04e09c26a2378272ec33aa0c1bf4883ca5ab739e8b7e06be5a5787d61:1               3848399 2007724 No
+Added   f85e3b4b89270863a389395cc9a4123e417ab19384cef96533c6649abd6b0561:0               3788399 2094513 No
+Added   f85e3b4b89270863a389395cc9a4123e417ab19384cef96533c6649abd6b0561:2                   540 2094513 No
+Spent   a05880b8c77971ed0b9f73062c7c4cdb0ff3856ab14cbf8bc481ed571cd34b83:1            5591281046 2094511 No
+Added   eb689865f7d957938978d6207918748f74e6aa074f47874724327089445b0960:0            5589696005 2094513 No
+Added   eb689865f7d957938978d6207918748f74e6aa074f47874724327089445b0960:1               1565556 2094513 No
+```

contrib/tracing/log_utxocache_flush.py

@@ -0,0 +1,107 @@
+#!/usr/bin/env python3
+
+import sys
+import ctypes
+from bcc import BPF, USDT
+
+"""Example logging Bitcoin Core utxo set cache flushes utilizing
+    the utxocache:flush tracepoint."""
+
+# USAGE:  ./contrib/tracing/log_utxocache_flush.py path/to/bitcoind
+
+# BCC: The C program to be compiled to an eBPF program (by BCC) and loaded into
+# a sandboxed Linux kernel VM.
+program = """
+# include <uapi/linux/ptrace.h>
+struct data_t
+{
+  u64 duration;
+  u32 mode;
+  u64 coins_count;
+  u64 coins_mem_usage;
+  bool is_flush_prune;
+  bool is_full_flush;
+};
+
+// BPF perf buffer to push the data to user space.
+BPF_PERF_OUTPUT(flush);
+
+int trace_flush(struct pt_regs *ctx) {
+  struct data_t data = {};
+  bpf_usdt_readarg(1, ctx, &data.duration);
+  bpf_usdt_readarg(2, ctx, &data.mode);
+  bpf_usdt_readarg(3, ctx, &data.coins_count);
+  bpf_usdt_readarg(4, ctx, &data.coins_mem_usage);
+  bpf_usdt_readarg(5, ctx, &data.is_flush_prune);
+  bpf_usdt_readarg(5, ctx, &data.is_full_flush);
+  flush.perf_submit(ctx, &data, sizeof(data));
+  return 0;
+}
+"""
+
+FLUSH_MODES = [
+    'NONE',
+    'IF_NEEDED',
+    'PERIODIC',
+    'ALWAYS'
+]
+
+
+class Data(ctypes.Structure):
+    # define output data structure corresponding to struct data_t
+    _fields_ = [
+        ("duration", ctypes.c_uint64),
+        ("mode", ctypes.c_uint32),
+        ("coins_count", ctypes.c_uint64),
+        ("coins_mem_usage", ctypes.c_uint64),
+        ("is_flush_prune", ctypes.c_bool),
+        ("is_full_flush", ctypes.c_bool)
+    ]
+
+
+def print_event(event):
+    print("%-15d %-10s %-15d %-15s %-8s %-8s" % (
+        event.duration,
+        FLUSH_MODES[event.mode],
+        event.coins_count,
+        "%.2f kB" % (event.coins_mem_usage/1000),
+        event.is_flush_prune,
+        event.is_full_flush
+    ))
+
+
+def main(bitcoind_path):
+    bitcoind_with_usdts = USDT(path=str(bitcoind_path))
+
+    # attaching the trace functions defined in the BPF program
+    # to the tracepoints
+    bitcoind_with_usdts.enable_probe(
+        probe="flush", fn_name="trace_flush")
+    b = BPF(text=program, usdt_contexts=[bitcoind_with_usdts])
+
+    def handle_flush(_, data, size):
+        """ Coins Flush handler.
+          Called each time coin caches and indexes are flushed."""
+        event = ctypes.cast(data, ctypes.POINTER(Data)).contents
+        print_event(event)
+
+    b["flush"].open_perf_buffer(handle_flush)
+    print("Logging utxocache flushes. Ctrl-C to end...")
+    print("%-15s %-10s %-15s %-15s %-8s %-8s" % ("Duration (µs)", "Mode",
+                                                 "Coins Count", "Memory Usage",
+                                                 "Prune", "Full Flush"))
+
+    while True:
+        try:
+            b.perf_buffer_poll()
+        except KeyboardInterrupt:
+            exit(0)
+
+
+if __name__ == "__main__":
+    if len(sys.argv) < 2:
+        print("USAGE: ", sys.argv[0], "path/to/bitcoind")
+        exit(1)
+
+    path = sys.argv[1]
+    main(path)

contrib/tracing/log_utxos.bt

@@ -0,0 +1,86 @@
+#!/usr/bin/env bpftrace
+
+/*
+
+  USAGE:
+
+  bpftrace contrib/tracing/log_utxos.bt
+
+  This script requires a 'bitcoind' binary compiled with eBPF support and the
+  'utxochache' tracepoints. By default, it's assumed that 'bitcoind' is
+  located in './src/bitcoind'. This can be modified in the script below.
+
+  NOTE: requires bpftrace v0.12.0 or above.
+*/
+
+BEGIN
+{
+    printf("%-7s %-71s %16s %7s %8s\n",
+          "OP", "Outpoint", "Value", "Height", "Coinbase");
+}
+
+/*
+  Attaches to the 'utxocache:add' tracepoint and prints additions to the UTXO set cache.
+*/
+usdt:./src/bitcoind:utxocache:add
+{
+  $txid = arg0;
+  $index = (uint32)arg1;
+  $height = (uint32)arg2;
+  $value = (int64)arg3;
+  $isCoinbase = arg4;
+
+  printf("Added   ");
+  $p = $txid + 31;
+  unroll(32) {
+    $b = *(uint8*)$p;
+    printf("%02x", $b);
+    $p-=1;
+  }
+
+  printf(":%-6d %16ld %7d %s\n", $index, $value, $height, ($isCoinbase ? "Yes" : "No" ));
+}
+
+/*
+  Attaches to the 'utxocache:spent' tracepoint and prints spents from the UTXO set cache.
+*/
+usdt:./src/bitcoind:utxocache:spent
+{
+  $txid = arg0;
+  $index = (uint32)arg1;
+  $height = (uint32)arg2;
+  $value = (int64)arg3;
+  $isCoinbase = arg4;
+
+  printf("Spent   ");
+  $p = $txid + 31;
+  unroll(32) {
+    $b = *(uint8*)$p;
+    printf("%02x", $b);
+    $p-=1;
+  }
+
+  printf(":%-6d %16ld %7d %s\n", $index, $value, $height, ($isCoinbase ? "Yes" : "No" ));
+}
+
+/*
+  Attaches to the 'utxocache:uncache' tracepoint and uncache UTXOs from the UTXO set cache.
+*/
+usdt:./src/bitcoind:utxocache:uncache
+{
+  $txid = arg0;
+  $index = (uint32)arg1;
+  $height = (uint32)arg2;
+  $value = (int64)arg3;
+  $isCoinbase = arg4;
+
+  printf("Uncache ");
+  $p = $txid + 31;
+  unroll(32) {
+    $b = *(uint8*)$p;
+    printf("%02x", $b);
+    $p-=1;
+  }
+
+  printf(":%-6d %16ld %7d %s\n", $index, $value, $height, ($isCoinbase ? "Yes" : "No" ));
+}

doc/tracing.md

@@ -108,6 +108,55 @@ Arguments passed:
 5. SigOps in the Block (excluding coinbase SigOps) `uint64`
 6. Time it took to connect the Block in microseconds (µs) as `uint64`
 
+### Context `utxocache`
+
+#### Tracepoint `utxocache:flush`
+
+Is called *after* the caches and indexes are flushed depending on the mode
+`CChainState::FlushStateToDisk` is called with.
+
+Arguments passed:
+1. Duration in microseconds as `int64`
+2. Flush state mode as `uint32`. It's an enumerator class with values `0`
+   (`NONE`), `1` (`IF_NEEDED`), `2` (`PERIODIC`), `3` (`ALWAYS`)
+3. Number of coins flushed as `uint64`
+4. Memory usage in bytes as `uint64`
+5. If the flush was pruned as `bool`
+6. If it was full flush as `bool`
+
+#### Tracepoint `utxocache:add`
+
+It is called when a new coin is added to the UTXO cache.
+
+Arguments passed:
+1. Transaction ID (hash) as `pointer to unsigned chars` (i.e. 32 bytes in little-endian)
+2. Output index as `uint32`
+3. Block height the coin was added to the UTXO-set as  `uint32`
+4. Value of the coin as `int64`
+5. If the coin is a coinbase as `bool`
+
+#### Tracepoint `utxocache:spent`
+
+It is called when a coin is spent from the UTXO cache.
+
+Arguments passed:
+1. Transaction ID (hash) as `pointer to unsigned chars` (i.e. 32 bytes in little-endian)
+2. Output index as `uint32`
+3. Block height the coin was spent, as `uint32`
+4. Value of the coin as `int64`
+5. If the coin is a coinbase as `bool`
+
+#### Tracepoint `utxocache:uncache`
+
+It is called when the UTXO with the given outpoint is removed from the cache.
+
+Arguments passed:
+1. Transaction ID (hash) as `pointer to unsigned chars` (i.e. 32 bytes in little-endian)
+2. Output index as `uint32`
+3. Block height the coin was uncached, as `uint32`
+4. Value of the coin as `int64`
+. If the coin is a coinbase as `bool`
+
 ## Adding tracepoints to Bitcoin Core
 
 To add a new tracepoint, `#include <util/trace.h>` in the compilation unit where

src/coins.cpp

@@ -7,6 +7,7 @@
 #include <consensus/consensus.h>
 #include <logging.h>
 #include <random.h>
+#include <util/trace.h>
 #include <version.h>
 
 bool CCoinsView::GetCoin(const COutPoint &outpoint, Coin &coin) const { return false; }
@@ -95,6 +96,12 @@ void CCoinsViewCache::AddCoin(const COutPoint &outpoint, Coin&& coin, bool possi
     it->second.coin = std::move(coin);
     it->second.flags |= CCoinsCacheEntry::DIRTY | (fresh ? CCoinsCacheEntry::FRESH : 0);
     cachedCoinsUsage += it->second.coin.DynamicMemoryUsage();
+    TRACE5(utxocache, add,
+           outpoint.hash.data(),
+           (uint32_t)outpoint.n,
+           (uint32_t)coin.nHeight,
+           (int64_t)coin.out.nValue,
+           (bool)coin.IsCoinBase());
 }
 
 void CCoinsViewCache::EmplaceCoinInternalDANGER(COutPoint&& outpoint, Coin&& coin) {
@@ -120,6 +127,12 @@ bool CCoinsViewCache::SpendCoin(const COutPoint &outpoint, Coin* moveout) {
     CCoinsMap::iterator it = FetchCoin(outpoint);
     if (it == cacheCoins.end()) return false;
     cachedCoinsUsage -= it->second.coin.DynamicMemoryUsage();
+    TRACE5(utxocache, spent,
+           outpoint.hash.data(),
+           (uint32_t)outpoint.n,
+           (uint32_t)it->second.coin.nHeight,
+           (int64_t)it->second.coin.out.nValue,
+           (bool)it->second.coin.IsCoinBase());
     if (moveout) {
         *moveout = std::move(it->second.coin);
     }
@@ -231,6 +244,12 @@ void CCoinsViewCache::Uncache(const COutPoint& hash)
     CCoinsMap::iterator it = cacheCoins.find(hash);
     if (it != cacheCoins.end() && it->second.flags == 0) {
         cachedCoinsUsage -= it->second.coin.DynamicMemoryUsage();
+        TRACE5(utxocache, uncache,
+               hash.hash.data(),
+               (uint32_t)hash.n,
+               (uint32_t)it->second.coin.nHeight,
+               (int64_t)it->second.coin.out.nValue,
+               (bool)it->second.coin.IsCoinBase());
         cacheCoins.erase(it);
     }
 }

src/validation.cpp

@@ -2101,6 +2101,13 @@ bool CChainState::FlushStateToDisk(
             nLastFlush = nNow;
             full_flush_completed = true;
         }
+        TRACE6(utxocache, flush,
+               (int64_t)(GetTimeMicros() - nNow.count()), // in microseconds (µs)
+               (u_int32_t)mode,
+               (u_int64_t)coins_count,
+               (u_int64_t)coins_mem_usage,
+               (bool)fFlushForPrune,
+               (bool)fDoFullFlush);
     }
     if (full_flush_completed) {
         // Update best block in wallet (so we can detect restored wallets).