net/art: implement the Table type, a multi-level art route table.

Updates #7781 │ sec/op │ TableInsertion/ipv4/10 1.562µ ± 2% TableInsertion/ipv4/100 2.398µ ± 5% TableInsertion/ipv4/1000 2.097µ ± 3% TableInsertion/ipv4/10000 2.756µ ± 4% TableInsertion/ipv4/100000 2.473µ ± 13% TableInsertion/ipv6/10 7.649µ ± 2% TableInsertion/ipv6/100 12.09µ ± 3% TableInsertion/ipv6/1000 14.84µ ± 5% TableInsertion/ipv6/10000 14.72µ ± 8% TableInsertion/ipv6/100000 13.23µ ± 41% TableDelete/ipv4/10 378.4n ± 5% TableDelete/ipv4/100 366.9n ± 3% TableDelete/ipv4/1000 418.6n ± 3% TableDelete/ipv4/10000 609.2n ± 11% TableDelete/ipv4/100000 679.2n ± 28% TableDelete/ipv6/10 504.2n ± 4% TableDelete/ipv6/100 959.5n ± 12% TableDelete/ipv6/1000 1.436µ ± 6% TableDelete/ipv6/10000 1.772µ ± 15% TableDelete/ipv6/100000 1.172µ ± 113% TableGet/ipv4/10 32.14n ± 11% TableGet/ipv4/100 38.58n ± 2% TableGet/ipv4/1000 45.03n ± 2% TableGet/ipv4/10000 52.90n ± 7% TableGet/ipv4/100000 135.2n ± 11% TableGet/ipv6/10 41.55n ± 1% TableGet/ipv6/100 44.78n ± 2% TableGet/ipv6/1000 49.03n ± 2% TableGet/ipv6/10000 65.38n ± 5% TableGet/ipv6/100000 525.0n ± 39% │ avg-B/op │ TableInsertion/ipv4/10 25.18Ki ± 0% TableInsertion/ipv4/100 17.63Ki ± 0% TableInsertion/ipv4/1000 14.14Ki ± 0% TableInsertion/ipv4/10000 12.92Ki ± 0% TableInsertion/ipv4/100000 11.13Ki ± 0% TableInsertion/ipv6/10 76.87Ki ± 0% TableInsertion/ipv6/100 98.33Ki ± 0% TableInsertion/ipv6/1000 91.44Ki ± 0% TableInsertion/ipv6/10000 90.39Ki ± 0% TableInsertion/ipv6/100000 87.19Ki ± 0% TableDelete/ipv4/10 3.230 ± 0% TableDelete/ipv4/100 4.020 ± 0% TableDelete/ipv4/1000 3.990 ± 0% TableDelete/ipv4/10000 4.000 ± 0% TableDelete/ipv4/100000 4.000 ± 0% TableDelete/ipv6/10 16.00 ± 0% TableDelete/ipv6/100 16.00 ± 0% TableDelete/ipv6/1000 16.00 ± 0% TableDelete/ipv6/10000 16.00 ± 0% TableDelete/ipv6/100000 16.00 ± 0% │ avg-allocs/op │ TableInsertion/ipv4/10 2.900 ± 0% TableInsertion/ipv4/100 2.330 ± 0% TableInsertion/ipv4/1000 2.070 ± 0% TableInsertion/ipv4/10000 1.980 ± 0% TableInsertion/ipv4/100000 1.840 ± 0% TableInsertion/ipv6/10 6.800 ± 0% TableInsertion/ipv6/100 8.420 ± 0% TableInsertion/ipv6/1000 7.900 ± 0% TableInsertion/ipv6/10000 7.820 ± 0% TableInsertion/ipv6/100000 7.580 ± 0% TableDelete/ipv4/10 1.000 ± 0% TableDelete/ipv4/100 1.000 ± 0% TableDelete/ipv4/1000 1.000 ± 0% TableDelete/ipv4/10000 1.000 ± 0% TableDelete/ipv4/100000 1.000 ± 0% TableDelete/ipv6/10 1.000 ± 0% TableDelete/ipv6/100 1.000 ± 0% TableDelete/ipv6/1000 1.000 ± 0% TableDelete/ipv6/10000 1.000 ± 0% TableDelete/ipv6/100000 1.000 ± 0% │ routes/s │ TableInsertion/ipv4/10 640.3k ± 2% TableInsertion/ipv4/100 417.1k ± 5% TableInsertion/ipv4/1000 477.0k ± 3% TableInsertion/ipv4/10000 362.8k ± 5% TableInsertion/ipv4/100000 404.5k ± 15% TableInsertion/ipv6/10 130.7k ± 1% TableInsertion/ipv6/100 82.69k ± 3% TableInsertion/ipv6/1000 67.37k ± 5% TableInsertion/ipv6/10000 67.93k ± 9% TableInsertion/ipv6/100000 75.63k ± 29% TableDelete/ipv4/10 2.642M ± 6% TableDelete/ipv4/100 2.726M ± 3% TableDelete/ipv4/1000 2.389M ± 3% TableDelete/ipv4/10000 1.641M ± 12% TableDelete/ipv4/100000 1.472M ± 27% TableDelete/ipv6/10 1.984M ± 4% TableDelete/ipv6/100 1.042M ± 11% TableDelete/ipv6/1000 696.5k ± 6% TableDelete/ipv6/10000 564.4k ± 13% TableDelete/ipv6/100000 853.6k ± 53% │ addrs/s │ TableGet/ipv4/10 31.11M ± 10% TableGet/ipv4/100 25.92M ± 2% TableGet/ipv4/1000 22.21M ± 2% TableGet/ipv4/10000 18.91M ± 8% TableGet/ipv4/100000 7.397M ± 12% TableGet/ipv6/10 24.07M ± 1% TableGet/ipv6/100 22.33M ± 2% TableGet/ipv6/1000 20.40M ± 2% TableGet/ipv6/10000 15.30M ± 5% TableGet/ipv6/100000 1.905M ± 28% │ B/op │ TableGet/ipv4/10 4.000 ± 0% TableGet/ipv4/100 4.000 ± 0% TableGet/ipv4/1000 4.000 ± 0% TableGet/ipv4/10000 4.000 ± 0% TableGet/ipv4/100000 4.000 ± 0% TableGet/ipv6/10 16.00 ± 0% TableGet/ipv6/100 16.00 ± 0% TableGet/ipv6/1000 16.00 ± 0% TableGet/ipv6/10000 16.00 ± 0% TableGet/ipv6/100000 16.00 ± 0% │ allocs/op │ TableGet/ipv4/10 1.000 ± 0% TableGet/ipv4/100 1.000 ± 0% TableGet/ipv4/1000 1.000 ± 0% TableGet/ipv4/10000 1.000 ± 0% TableGet/ipv4/100000 1.000 ± 0% TableGet/ipv6/10 1.000 ± 0% TableGet/ipv6/100 1.000 ± 0% TableGet/ipv6/1000 1.000 ± 0% TableGet/ipv6/10000 1.000 ± 0% TableGet/ipv6/100000 1.000 ± 0% Signed-off-by: David Anderson <danderson@tailscale.com>
2025-12-03 02:21:58 +00:00 · 2023-04-04 09:00:51 -07:00
parent edb02b63f8
commit a7c910e361
4 changed files with 708 additions and 6 deletions
--- a/net/art/table.go
+++ b/net/art/table.go
@@ -11,3 +11,152 @@
 // For more information, see Yoichi Hariguchi's paper:
 // https://cseweb.ucsd.edu//~varghese/TEACH/cs228/artlookup.pdf
 package art
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/netip"
+	"strings"
+)
+
+// Table is an IPv4 and IPv6 routing table.
+type Table[T any] struct {
+	v4 strideTable[T]
+	v6 strideTable[T]
+}
+
+// Get does a route lookup for addr and returns the associated value, or nil if
+// no route matched.
+func (t *Table[T]) Get(addr netip.Addr) *T {
+	st := &t.v4
+	if addr.Is6() {
+		st = &t.v6
+	}
+
+	var ret *T
+	for _, stride := range addr.AsSlice() {
+		rt, child := st.getValAndChild(stride)
+		if rt != nil {
+			// Found a more specific route than whatever we found previously,
+			// keep a note.
+			ret = rt
+		}
+		if child == nil {
+			// No sub-routes further down, whatever we have recorded in ret is
+			// the result.
+			return ret
+		}
+		st = child
+	}
+
+	// Unreachable because Insert/Delete won't allow the leaf strideTables to
+	// have children, so we must return via the nil check in the loop.
+	panic("unreachable")
+}
+
+// Insert adds pfx to the table, with value val.
+// If pfx is already present in the table, its value is set to val.
+func (t *Table[T]) Insert(pfx netip.Prefix, val *T) {
+	if val == nil {
+		panic("Table.Insert called with nil value")
+	}
+	st := &t.v4
+	if pfx.Addr().Is6() {
+		st = &t.v6
+	}
+	bs := pfx.Addr().AsSlice()
+	i := 0
+	numBits := pfx.Bits()
+
+	// The strideTable we want to insert into is potentially at the end of a
+	// chain of parent tables, each one encoding successive 8 bits of the
+	// prefix. Navigate downwards, allocating child tables as needed, until we
+	// find the one this prefix belongs in.
+	for numBits > 8 {
+		st = st.getOrCreateChild(bs[i])
+		i++
+		numBits -= 8
+	}
+	// Finally, insert the remaining 0-8 bits of the prefix into the child
+	// table.
+	st.insert(bs[i], numBits, val)
+}
+
+// Delete removes pfx from the table, if it is present.
+func (t *Table[T]) Delete(pfx netip.Prefix) {
+	st := &t.v4
+	if pfx.Addr().Is6() {
+		st = &t.v6
+	}
+	bs := pfx.Addr().AsSlice()
+	i := 0
+	numBits := pfx.Bits()
+
+	// Deletion may drive the refcount of some strideTables down to zero. We
+	// need to clean up these dangling tables, so we have to keep track of which
+	// tables we touch on the way down, and which strideEntry index each child
+	// is registered in.
+	strideTables := [16]*strideTable[T]{st}
+	var strideIndexes [16]int
+
+	// Similar to Insert, navigate down the tree of strideTables, looking for
+	// the one that houses the last 0-8 bits of the prefix to delete.
+	//
+	// The only difference is that here, we don't create missing child tables.
+	// If a child necessary to pfx is missing, then the pfx cannot exist in the
+	// Table, and we can exit early.
+	for numBits > 8 {
+		child, idx := st.getChild(bs[i])
+		if child == nil {
+			// Prefix can't exist in the table, one of the necessary
+			// strideTables doesn't exit.
+			return
+		}
+		// Note that the strideIndex and strideTables entries are off-by-one.
+		// The child table pointer is recorded at i+1, but it is referenced by a
+		// particular index in the parent table, at index i.
+		strideIndexes[i] = idx
+		i++
+		strideTables[i] = child
+		numBits -= 8
+		st = child
+	}
+	if st.delete(bs[i], numBits) == nil {
+		// Prefix didn't exist in the expected strideTable, refcount hasn't
+		// changed, no need to run through cleanup.
+		return
+	}
+
+	// st.delete reduced st's refcount by one, so we may be hanging onto a chain
+	// of redundant strideTables. Walk back up the path we recorded in the
+	// descent loop, deleting tables until we encounter one that still has other
+	// refs (or we hit the root strideTable, which is never deleted).
+	for i > 0 && strideTables[i].refs == 0 {
+		strideTables[i-1].deleteChild(strideIndexes[i-1])
+		i--
+	}
+}
+
+// debugSummary prints the tree of allocated strideTables in t, with each
+// strideTable's refcount.
+func (t *Table[T]) debugSummary() string {
+	var ret bytes.Buffer
+	fmt.Fprintf(&ret, "v4: ")
+	strideSummary(&ret, &t.v4, 0)
+	fmt.Fprintf(&ret, "v6: ")
+	strideSummary(&ret, &t.v6, 0)
+	return ret.String()
+}
+
+func strideSummary[T any](w io.Writer, st *strideTable[T], indent int) {
+	fmt.Fprintf(w, "%d refs\n", st.refs)
+	indent += 2
+	for i := firstHostIndex; i <= lastHostIndex; i++ {
+		if child := st.entries[i].child; child != nil {
+			addr, len := inversePrefixIndex(i)
+			fmt.Fprintf(w, "%s%d/%d: ", strings.Repeat(" ", indent), addr, len)
+			strideSummary(w, child, indent)
+		}
+	}
+}