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fix: first hash of prefix cache with same model name #1341

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fix: first hash of prefix cache with same model name #1341

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592b5c9
fix: first hash of prefix cache with same model name
livelxw Aug 9, 2025
44c94fb
fix: no hash if the prompt is smaller than cacheBlockSize
livelxw Aug 12, 2025
60fae98
fix: optimize if else for more concise
livelxw Aug 13, 2025
0c08ea1
chore: clean test comments
livelxw Aug 13, 2025
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19 changes: 12 additions & 7 deletions pkg/epp/scheduling/framework/plugins/multi/prefix/plugin.go
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Original file line number Diff line number Diff line change
Expand Up @@ -257,16 +257,21 @@ func hashPrompt(ctx context.Context, request *types.LLMRequest, cacheBlockSize i
// If the last block is smaller than cacheBlockSize, it will be ignored.
res := make([]BlockHash, 0, 1+len(prompt)/cacheBlockSize)
// Add the model to the first block hash so that different models have different hashes even with the same body.
if len(prompt) >= cacheBlockSize {
if len(prompt) < cacheBlockSize {
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This is a bit nitpicking but can we just converge the if/else to the below. It's much concise and more readable in my opinion.

firstBlockSize = cacheBlockSize
if len(prompt) < cacheBlockSize {
  firstBlockSize = len(prompt)
}
firstBlock := prompt[0:firstBlockSize]
firstBlockWithModel := append([]byte(request.TargetModel), firstBlock...)
res = append(res, BlockHash(xxhash.Sum64(firstBlockWithModel)))

firstBlockSize := len(prompt)
firstBlock := prompt[0:firstBlockSize]
firstBlockWithModel := append([]byte(request.TargetModel), firstBlock...)
res = append(res, BlockHash(xxhash.Sum64(firstBlockWithModel)))
} else {
firstBlock := prompt[0:cacheBlockSize]
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The current implementation will lead to no hash if the prompt is smaller than cacheBlockSize. I suggest the below modification instead:

firstBlockSize = cacheBlockSize
if len(prompt) < cacheBlockSize {
  firstBlockSize = len(prompt)
}
firstBlock := prompt[0:firstBlockSize]
firstBlockWithModel := append([]byte(request.TargetModel), firstBlock...)
res = append(res, BlockHash(xxhash.Sum64(firstBlockWithModel)))

combined := append([]byte(request.TargetModel), firstBlock...)
res = append(res, BlockHash(xxhash.Sum64(combined)))
}
for i := cacheBlockSize; i+cacheBlockSize <= len(prompt); i += cacheBlockSize {
block := prompt[i : i+cacheBlockSize]
prevBlockHash := res[len(res)-1]
block = append(block, toBytes(prevBlockHash)...)
res = append(res, BlockHash(xxhash.Sum64(block)))
for i := cacheBlockSize; i+cacheBlockSize <= len(prompt); i += cacheBlockSize {
block := prompt[i : i+cacheBlockSize]
prevBlockHash := res[len(res)-1]
block = append(block, toBytes(prevBlockHash)...)
res = append(res, BlockHash(xxhash.Sum64(block)))
}
}
return res
}
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24 changes: 12 additions & 12 deletions pkg/epp/scheduling/framework/plugins/multi/prefix/plugin_test.go
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Expand Up @@ -55,8 +55,8 @@ func TestPrefixPlugin(t *testing.T) {
assert.NoError(t, err)
t.Logf("Hashes %+v, cached servers: %+v", state.PrefixHashes, state.PrefixCacheServers)
// Input size is 6, hash block size is 4, the last 2 characters are ignored.
// Total hashes = 2 (the first one is for the model)
assert.Equal(t, 2, len(state.PrefixHashes), "number of hashes is incorrect")
// Total hashes = 1 (the first one is for the prefix with model)
assert.Equal(t, 1, len(state.PrefixHashes), "number of hashes is incorrect")
assert.Equal(t, 0, len(state.PrefixCacheServers), "there shouldn't be any cached servers")
assert.Equal(t, float64(0), scores[pod1], "score for pod1")
assert.Equal(t, float64(0), scores[pod2], "score for pod2")
Expand All @@ -76,8 +76,8 @@ func TestPrefixPlugin(t *testing.T) {
assert.NoError(t, err)
t.Logf("Hashes %+v, cached servers: %+v", state.PrefixHashes, state.PrefixCacheServers)
// Input size is 6, hash block size is 4, the last 2 characters are ignored.
// Total hashes = 2 (the first one is for the model)
assert.Equal(t, 2, len(state.PrefixHashes), "number of hashes is incorrect")
// Total hashes = 1 (the first one is for the prefix with model)
assert.Equal(t, 1, len(state.PrefixHashes), "number of hashes is incorrect")
assert.Equal(t, 0, len(state.PrefixCacheServers), "there shouldn't be any cached servers")
assert.Equal(t, float64(0), scores[pod1], "score for pod1")
assert.Equal(t, float64(0), scores[pod2], "score for pod2")
Expand All @@ -96,10 +96,10 @@ func TestPrefixPlugin(t *testing.T) {
assert.NoError(t, err)
t.Logf("Hashes %+v, cached servers: %+v", state.PrefixHashes, state.PrefixCacheServers)
// Input size is 8, hash block size is 4, so 2 hashes will be calculated.
// Total hashes = 3 (the first one is for the model)
assert.Equal(t, 3, len(state.PrefixHashes), "number of hashes is incorrect")
// Total hashes = 2 (the first one is for the prefix with model)
assert.Equal(t, 2, len(state.PrefixHashes), "number of hashes is incorrect")
assert.Equal(t, 1, len(state.PrefixCacheServers), "pod1 should have cached the aaaa prefix")
assert.Equal(t, float64(2)/float64(3), scores[pod1], "score should be 2/3 - the model and the first prefix block match")
assert.Equal(t, 0.5, scores[pod1], "score should be 0.5 - the model and the first prefix block match")
assert.Equal(t, float64(0), scores[pod2], "score for pod2")

plugin.PostCycle(context.Background(), cycleState3, &types.ProfileRunResult{TargetPods: []types.Pod{pod1}})
Expand All @@ -115,8 +115,8 @@ func TestPrefixPlugin(t *testing.T) {
assert.NoError(t, err)
t.Logf("Hashes %+v, cached servers: %+v", state.PrefixHashes, state.PrefixCacheServers)
// Input size is 8, hash block size is 4, so 2 hashes will be calculated.
// Total hashes = 3 (the first one is for the model)
assert.Equal(t, 3, len(state.PrefixHashes), "number of hashes is incorrect")
// Total hashes = 2 (the first one is for the prefix with model)
assert.Equal(t, 2, len(state.PrefixHashes), "number of hashes is incorrect")
assert.Equal(t, 0, len(state.PrefixCacheServers), "pod1 should have cached the aaaa prefix")
assert.Equal(t, float64(0), scores[pod1], "score for pod1")
assert.Equal(t, float64(0), scores[pod2], "score for pod2")
Expand All @@ -134,10 +134,10 @@ func TestPrefixPlugin(t *testing.T) {
assert.NoError(t, err)
t.Logf("Hashes %+v, cached servers: %+v", state.PrefixHashes, state.PrefixCacheServers)
// Input size is 12, hash block size is 4, so 3 hashes will be calculated.
// Total hashes = 4 (the first one is for the model)
assert.Equal(t, 4, len(state.PrefixHashes), "number of hashes is incorrect")
// Total hashes = 3 (the first one is for the prefix with model)
assert.Equal(t, 3, len(state.PrefixHashes), "number of hashes is incorrect")
assert.Equal(t, 1, len(state.PrefixCacheServers), "pod1 should have cached the aaaa prefix")
assert.Equal(t, 0.75, scores[pod1], "score should be 0.75 - the model and the first 2 prefix blocks match")
assert.Equal(t, 2./3, scores[pod1], "score should be 2./3 - the model and the first 2 prefix blocks match")
assert.Equal(t, float64(0), scores[pod2], "score for pod2")

plugin.PostCycle(context.Background(), cycleState5, &types.ProfileRunResult{TargetPods: []types.Pod{pod1}})
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