feature/prefix-aware-routing (vllm-project#546)

* feat: add vllmruntime

Signed-off-by: BrianPark314 <brianpark314@gmail.com>

* feat: add prefix aware picker

Signed-off-by: BrianPark314 <brianpark314@gmail.com>

* feat: add prefix aware picker

Signed-off-by: BrianPark314 <brianpark314@gmail.com>

* feat: update prefix aware logic

Signed-off-by: BrianPark314 <brianpark314@gmail.com>

* chore: revert roundrobin picker

Signed-off-by: BrianPark314 <brianpark314@gmail.com>

* chore: fix pa picker logic

Signed-off-by: BrianPark314 <brianpark314@gmail.com>

* chore: add newline

Signed-off-by: BrianPark314 <brianpark314@gmail.com>

---------

Signed-off-by: BrianPark314 <brianpark314@gmail.com>
Co-authored-by: BrianPark314 <brianpark314@gmail.com>
Co-authored-by: Yuhan Liu <32589867+YuhanLiu11@users.noreply.github.com>

Author: 3 people

src/gateway_inference_extension/prefix_aware_picker.go

@@ -0,0 +1,213 @@
+/*
+Copyright 2025 The vLLM Production Stack Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+*/
+
+package picker
+
+import (
+	"math/rand"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/cespare/xxhash/v2"
+
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/plugins"
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/types"
+)
+
+const chunkSize = 128
+
+var _ plugins.Picker = &PrefixMatchPicker{}
+
+// PrefixMatchPicker selects the engine whose URL was returned by the
+// longest-prefix match against previously-seen prompts (same idea as the
+// Python `route_request`). Ties are broken at random.
+type PrefixMatchPicker struct {
+	trie *hashTrie
+	rnd  *rand.Rand
+}
+
+// NewPrefixMatchPicker returns a ready-to-use picker instance.
+func NewPrefixMatchPicker() *PrefixMatchPicker {
+	return &PrefixMatchPicker{
+		trie: newHashTrie(),
+		rnd:  rand.New(rand.NewSource(time.Now().UnixNano())),
+	}
+}
+
+func (p *PrefixMatchPicker) Name() string { return "prefixmatch" }
+
+// Pick implements plugins.Picker.
+//
+// SchedulingContext is assumed to carry the inference request body in
+// ctx.RequestBody (map[string]any) with the prompt at key "prompt".  Adjust
+// the accessor if your integration differs.
+func (p *PrefixMatchPicker) Pick(
+	ctx *types.SchedulingContext,
+	scoredPods []*types.ScoredPod,
+) *types.Result {
+	if len(scoredPods) == 0 {
+		return &types.Result{}
+	}
+
+	var prompt string
+
+	if msgs, ok := ctx.RequestBody["messages"]; ok {
+		if arr, ok := msgs.([]any); ok {
+			var parts []string
+			for _, m := range arr {
+				mm, ok := m.(map[string]any)
+				if !ok {
+					continue
+				}
+				switch c := mm["content"].(type) {
+				case string:
+					parts = append(parts, c)
+				case []any:
+					for _, part := range c {
+						mp, ok := part.(map[string]any)
+						if !ok {
+							continue
+						}
+						if mp["type"] == "text" {
+							if txt, ok := mp["text"].(string); ok {
+								parts = append(parts, txt)
+							}
+						}
+					}
+				}
+			}
+			prompt = strings.Join(parts, "\n")
+		}
+	}
+
+	if prompt == "" {
+		prompt, _ = ctx.RequestBody["prompt"].(string)
+	}
+
+	// 1. Build the set of available endpoints.
+	available := make(map[string]struct{}, len(scoredPods))
+	for _, sp := range scoredPods {
+		ep := sp.GetPod().EndpointURL // <-- adapt this accessor
+		available[ep] = struct{}{}
+	}
+
+	// 2. Longest-prefix match within the trie.
+	matched := p.trie.longestPrefixMatch(prompt, available)
+
+	// 3. Fallback: no match --> all endpoints are candidates.
+	if len(matched) == 0 {
+		for ep := range available {
+			matched[ep] = struct{}{}
+		}
+	}
+
+	// 4. Convert the matched set to a slice and pick randomly.
+	endpoints := make([]string, 0, len(matched))
+	for ep := range matched {
+		endpoints = append(endpoints, ep)
+	}
+	selected := endpoints[p.rnd.Intn(len(endpoints))]
+
+	// 5. Cache the decision for future prefix look-ups.
+	p.trie.insert(prompt, selected)
+
+	// 6. Return the pod whose URL matches `selected`.
+	for _, sp := range scoredPods {
+		if sp.GetPod().EndpointURL == selected { // same accessor as above
+			return &types.Result{TargetPod: sp}
+		}
+	}
+	// Should never hit; safe fallback.
+	return &types.Result{TargetPod: scoredPods[0]}
+}
+
+/*---------------------------- trie implementation ---------------------------*/
+
+type hashTrie struct {
+	mu        sync.RWMutex
+	children  map[uint64]*hashTrie
+	endpoints map[string]struct{}
+}
+
+func newHashTrie() *hashTrie {
+	return &hashTrie{children: make(map[uint64]*hashTrie)}
+}
+
+func intersection(a, b map[string]struct{}) map[string]struct{} {
+	res := make(map[string]struct{})
+	for k := range a {
+		if _, ok := b[k]; ok {
+			res[k] = struct{}{}
+		}
+	}
+	return res
+}
+
+func chunkAndHash(s string) []uint64 {
+	hashes := make([]uint64, 0, (len(s)+chunkSize-1)/chunkSize)
+	for i := 0; i < len(s); i += chunkSize {
+		end := i + chunkSize
+		if end > len(s) {
+			end = len(s)
+		}
+		hashes = append(hashes, xxhash.Sum64([]byte(s[i:end])))
+	}
+	return hashes
+}
+
+func (t *hashTrie) insert(key, endpoint string) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	node := t
+	if node.endpoints == nil {
+		node.endpoints = make(map[string]struct{})
+	}
+	node.endpoints[endpoint] = struct{}{}
+
+	for _, h := range chunkAndHash(key) {
+		child, ok := node.children[h]
+		if !ok {
+			child = newHashTrie()
+			node.children[h] = child
+		}
+		node = child
+		if node.endpoints == nil {
+			node.endpoints = make(map[string]struct{})
+		}
+		node.endpoints[endpoint] = struct{}{}
+	}
+}
+
+func (t *hashTrie) longestPrefixMatch(
+	key string,
+	available map[string]struct{},
+) map[string]struct{} {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+
+	node := t
+	matched := intersection(node.endpoints, available)
+
+	for _, h := range chunkAndHash(key) {
+		child, ok := node.children[h]
+		if !ok {
+			break
+		}
+		node = child
+		cand := intersection(node.endpoints, available)
+		if len(cand) == 0 {
+			break
+		}
+		matched = cand
+	}
+	return matched
+}

src/gateway_inference_extension/scheduler.patch

@@ -16,6 +16,7 @@ index b484cde..c7688a8 100644
  		scorers:             map[plugins.Scorer]int{},
 -		picker:              &picker.RandomPicker{},
 +		picker:              &picker.RoundRobinPicker{},
++       picker:              &picker.PrefixAwarePicker{},
  		postSchedulePlugins: []plugins.PostSchedule{},
  	}