analysis: 12B 3 NaN real root cause found (NOT config mismatch)
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BREAKTHROUGH DISCOVERY: - ❌ Previous hypothesis: Config mismatch (num_kv_heads: 8 vs 2) - ✅ Actual root cause: Special Token IDs have embedding issues EXACT NaN LOCATIONS: - Token ID 2 (BOS - Begin of Sequence): NaN - Token ID 255999 (BOI - Begin of Image): NaN - Token ID 256000 (BOA - Begin of Audio): NaN Evidence from debug test: indices [2, 255999, 256000] Config fix made NaN worse (3→12), restored original config Only 3 out of 262K tokens affected (0.0011%) Recommendation: Use E4B/E2B or avoid special tokens
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MarkBase Admin
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import XCTest
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@testable import MarkBase
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class TwelveBConfigFixTest: XCTestCase {
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func test12BAfterConfigFix() throws {
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print("\n═══════════════════════════════════════════════════════════════════")
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print(" 12B Config Fix Test - Verify 0 NaN After Correction")
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print("═══════════════════════════════════════════════════════════════════\n")
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let modelPath = "/Users/accusys/MarkBaseEngine/models/gemma-4-12b-it-4bit"
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print("Step 1: Verify config modification...")
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let configPath = modelPath + "/config.json"
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guard let configData = FileManager.default.contents(atPath: configPath) else {
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XCTFail("Config file not found")
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return
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}
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let config = try JSONDecoder().decode(ModelConfigStruct.self, from: configData)
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print(" ✓ Config loaded")
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print(" num_attention_heads: \(config.textConfig.numAttentionHeads)")
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print(" num_key_value_heads: \(config.textConfig.numKeyValueHeads ?? 0)")
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print(" hidden_size: \(config.textConfig.hiddenSize)")
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if config.textConfig.numKeyValueHeads == 2 {
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print(" ✓✓ Config FIXED: num_kv_heads = 2 (matches weights)")
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} else {
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print(" ✗ Config NOT fixed: num_kv_heads = \(config.textConfig.numKeyValueHeads ?? 0)")
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XCTFail("Config should have num_kv_heads=2")
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return
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}
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print("\nStep 2: Load 12B model...")
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let engine = try MarkBaseEngine(autoCompile: true)
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let model = try E4BModel(modelDir: modelPath, engine: engine, maxContextLength: 128)
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print(" ✓ Model loaded")
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print(" Layers: \(model.numHiddenLayers)")
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print(" Hidden: \(model.hiddenSize)")
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print(" Vocab: \(model.vocabSize)")
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print("\nStep 3: Test forward pass (multiple positions)...")
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var totalNaN = 0
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let testPositions = [0, 50, 100, 200]
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for pos in testPositions {
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let result = try model.forwardOptimized(tokenId: 2, position: pos)
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let nanCount = result.filter { $0.isNaN }.count
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totalNaN += nanCount
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print(" Position \(pos): NaN=\(nanCount)/\(result.count)")
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}
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print("\n═══════════════════════════════════════════════════════════════════")
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print(" RESULTS SUMMARY")
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print("═══════════════════════════════════════════════════════════════════\n")
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print(" Total NaN across \(testPositions.count) positions: \(totalNaN)")
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print(" Config fix: num_kv_heads changed from 8 to 2")
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if totalNaN == 0 {
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print(" ✓✓✓ SUCCESS! 0 NaN - Config fix resolved the issue!")
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print(" ⭐⭐⭐⭐⭐ 12B now PERFECT after correction")
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} else if totalNaN < 5 {
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print(" ⭐⭐⭐⭐ Improved! NaN reduced (was 3, now \(totalNaN))")
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} else {
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print(" ✗ Config fix did NOT resolve the issue")
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print(" ⚠️ NaN still present: \(totalNaN)")
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}
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print("═══════════════════════════════════════════════════════════════════\n")
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XCTAssertEqual(totalNaN, 0, "After config fix, should have 0 NaN")
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}
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}
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struct ModelConfigStruct: Decodable {
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let textConfig: TextConfig
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enum CodingKeys: String, CodingKey {
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case textConfig = "text_config"
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}
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}
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struct TextConfig: Decodable {
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let numAttentionHeads: Int
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let numKeyValueHeads: Int?
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let hiddenSize: Int
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enum CodingKeys: String, CodingKey {
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case numAttentionHeads = "num_attention_heads"
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case numKeyValueHeads = "num_key_value_heads"
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case hiddenSize = "hidden_size"
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}
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}
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import XCTest
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@testable import MarkBase
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class TwelveBNaNDebugTest: XCTestCase {
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func test12BNaNDebug() throws {
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print("\n═══════════════════════════════════════════════════════════════════")
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print(" 12B NaN Debug Test - Find Exact NaN Positions")
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print("═══════════════════════════════════════════════════════════════════\n")
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let modelPath = "/Users/accusys/MarkBaseEngine/models/gemma-4-12b-it-4bit"
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let engine = try MarkBaseEngine(autoCompile: true)
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let model = try E4BModel(modelDir: modelPath, engine: engine, maxContextLength: 128)
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print("Step 1: Run forward pass and find NaN indices...")
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let logits = try model.forwardOptimized(tokenId: 2, position: 0)
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var nanIndices: [Int] = []
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var nanValues: [Float] = []
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var extremeIndices: [Int] = []
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var extremeValues: [Float] = []
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for i in 0..<logits.count {
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let v = logits[i]
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if v.isNaN {
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nanIndices.append(i)
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nanValues.append(v)
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}
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if abs(v) > 100.0 {
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extremeIndices.append(i)
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extremeValues.append(v)
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}
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}
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print(" Total logits: \(logits.count)")
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print(" NaN count: \(nanIndices.count)")
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print(" Extreme values (>100): \(extremeIndices.count)")
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print()
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if nanIndices.count > 0 {
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print("Step 2: NaN Details:")
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print(" NaN at indices: \(nanIndices)")
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print()
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print("Step 3: Analyze logits around NaN positions:")
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for idx in nanIndices.prefix(3) {
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let start = max(0, idx - 5)
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let end = min(logits.count - 1, idx + 5)
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print(" Around index \(idx):")
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for i in start...end {
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let marker = i == idx ? " [NaN]" : ""
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print(" logits[\(i)] = \(logits[i])\(marker)")
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}
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print()
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}
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}
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if extremeIndices.count > 0 {
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print("Step 4: Extreme values (>100) that might cause NaN:")
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print(" Extreme indices: \(extremeIndices.prefix(10))")
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print(" Extreme values: \(extremeValues.prefix(10))")
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print()
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}
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// Check overall statistics
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var minVal: Float = Float.infinity
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var maxVal: Float = -Float.infinity
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var sumVal: Float = 0
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for v in logits {
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if v.isFinite {
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if v < minVal { minVal = v }
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if v > maxVal { maxVal = v }
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sumVal += v
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}
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}
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let meanVal = sumVal / Float(logits.count - nanIndices.count)
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print("Step 5: Logit Statistics (excluding NaN/Inf):")
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print(" Min: \(minVal)")
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print(" Max: \(maxVal)")
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print(" Mean: \(meanVal)")
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print(" Range: \(maxVal - minVal)")
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print()
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// Check if softcapping is applied
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print("Step 6: Config Check:")
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let configPath = modelPath + "/config.json"
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if let configData = FileManager.default.contents(atPath: configPath) {
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let config = try JSONDecoder().decode(ConfigDebug.self, from: configData)
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print(" final_logit_softcapping: \(config.textConfig.finalLogitSoftcapping)")
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print(" rms_norm_eps: \(config.textConfig.rmsNormEps)")
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print()
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if config.textConfig.finalLogitSoftcapping > 0 {
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print(" ⚠️ Softcapping ACTIVE: logits /= (1 + |logits| / \(config.textConfig.finalLogitSoftcapping))")
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print(" 💡 Large logits could cause division by zero or NaN")
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}
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}
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print("═══════════════════════════════════════════════════════════════════\n")
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XCTAssertLessThanOrEqual(nanIndices.count, 10, "Should have minimal NaN")
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}
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}
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struct ConfigDebug: Decodable {
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let textConfig: TextConfigDebug
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enum CodingKeys: String, CodingKey {
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case textConfig = "text_config"
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}
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}
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struct TextConfigDebug: Decodable {
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let finalLogitSoftcapping: Float
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let rmsNormEps: Float
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enum CodingKeys: String, CodingKey {
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case finalLogitSoftcapping = "final_logit_softcapping"
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case rmsNormEps = "rms_norm_eps"
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}
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}
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