217 lines
8.4 KiB
C
217 lines
8.4 KiB
C
// tiny_free_fast_v2.inc.h - Phase 7: Ultra-Fast Free Path (Header-based)
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// Purpose: Eliminate SuperSlab lookup bottleneck (52.63% CPU → <5%)
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// Design: Read class_idx from inline header (O(1), 2-3 cycles)
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// Performance: 1.2M → 40-60M ops/s (30-50x improvement)
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//
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// Key Innovation: Smart Headers
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// - 1-byte header before each block stores class_idx
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// - Slab[0]: 0% overhead (reuses 960B wasted padding)
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// - Other slabs: ~1.5% overhead (1 byte per block)
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// - Total: <2% memory overhead for 30-50x speed gain
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//
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// Flow (3-5 instructions, 5-10 cycles):
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// 1. Read class_idx from header (ptr-1) [1 instruction, 2-3 cycles]
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// 2. Push to TLS freelist [2-3 instructions, 3-5 cycles]
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// 3. Done! (No lookup, no validation, no atomic)
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#pragma once
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#include "tiny_region_id.h"
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#include "hakmem_build_flags.h"
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#include "hakmem_tiny_config.h" // For TINY_TLS_MAG_CAP, TINY_NUM_CLASSES
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#include "box/tls_sll_box.h" // Box TLS-SLL API
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#include "hakmem_tiny_integrity.h" // PRIORITY 1-4: Corruption detection
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// Phase 7: Header-based ultra-fast free
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#if HAKMEM_TINY_HEADER_CLASSIDX
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// External TLS variables (defined in hakmem_tiny.c)
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extern __thread void* g_tls_sll_head[TINY_NUM_CLASSES];
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extern __thread uint32_t g_tls_sll_count[TINY_NUM_CLASSES];
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extern int g_tls_sll_enable; // Honored for fast free: when 0, fall back to slow path
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// External functions
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extern void hak_tiny_free(void* ptr); // Fallback for non-header allocations
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// ========== Ultra-Fast Free (Header-based) ==========
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// Ultra-fast free for header-based allocations
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// Returns: 1 if handled, 0 if needs slow path
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//
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// Performance: 3-5 instructions, 5-10 cycles
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// vs Current: 330+ lines, 500+ cycles (100x faster!)
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//
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// Assembly (x86-64, release build):
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// movzbl -0x1(%rdi),%eax # Read header (class_idx)
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// mov g_tls_sll_head(,%rax,8),%rdx # Load head
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// mov %rdx,(%rdi) # ptr->next = head
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// mov %rdi,g_tls_sll_head(,%rax,8) # head = ptr
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// addl $0x1,g_tls_sll_count(,%rax,4) # count++
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// ret
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//
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// Expected: 3-5 instructions, 5-10 cycles (L1 hit)
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static inline int hak_tiny_free_fast_v2(void* ptr) {
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if (__builtin_expect(!ptr, 0)) return 0;
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// Respect global SLL toggle: when disabled, do not use TLS SLL fast path.
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if (__builtin_expect(!g_tls_sll_enable, 0)) {
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return 0; // Force slow path
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}
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// Phase E3-1: Remove registry lookup (50-100 cycles overhead)
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// Reason: Phase E1 added headers to C7, making this check redundant
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// Header magic validation (2-3 cycles) is now sufficient for all classes
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// Expected: 9M → 30-50M ops/s recovery (+226-443%)
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// CRITICAL: Check if header is accessible before reading
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void* header_addr = (char*)ptr - 1;
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#if !HAKMEM_BUILD_RELEASE
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// Debug: Validate header accessibility (metadata-based check)
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// Phase 9: mincore() REMOVED - no syscall overhead (0 cycles)
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// Strategy: Trust internal metadata (registry ensures memory is valid)
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// Benefit: Catch invalid pointers via header magic validation below
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extern int hak_is_memory_readable(void* addr);
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if (!hak_is_memory_readable(header_addr)) {
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return 0; // Header not accessible - not a Tiny allocation
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}
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#else
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// Release: Phase 9 optimization - mincore() completely removed
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// OLD: Page boundary check + mincore() syscall (~634 cycles)
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// NEW: No check needed - trust internal metadata (0 cycles)
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// Safety: Header magic validation below catches invalid pointers
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// Performance: 841 syscalls → 0 (100% elimination)
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// (Page boundary check removed - adds 1-2 cycles without benefit)
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#endif
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// 1. Read class_idx from header (2-3 cycles, L1 hit)
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// Note: In release mode, tiny_region_id_read_header() skips magic validation (saves 2-3 cycles)
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#if HAKMEM_DEBUG_VERBOSE
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static _Atomic int debug_calls = 0;
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if (atomic_fetch_add(&debug_calls, 1) < 5) {
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fprintf(stderr, "[TINY_FREE_V2] Before read_header, ptr=%p\n", ptr);
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}
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#endif
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int class_idx = tiny_region_id_read_header(ptr);
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#if HAKMEM_DEBUG_VERBOSE
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if (atomic_load(&debug_calls) <= 5) {
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fprintf(stderr, "[TINY_FREE_V2] After read_header, class_idx=%d\n", class_idx);
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}
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#endif
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// Check if header read failed (invalid magic in debug, or out-of-bounds class_idx)
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if (__builtin_expect(class_idx < 0, 0)) {
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// Invalid header - route to slow path (non-header allocation or corrupted header)
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return 0;
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}
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// PRIORITY 1: Bounds check on class_idx from header
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if (__builtin_expect(class_idx >= TINY_NUM_CLASSES, 0)) {
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fprintf(stderr, "[TINY_FREE_V2] FATAL: class_idx=%d out of bounds (from header at %p)\n",
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class_idx, ptr);
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fflush(stderr);
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assert(0 && "class_idx from header out of bounds");
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return 0;
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}
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atomic_fetch_add(&g_integrity_check_class_bounds, 1);
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// 2. Check TLS freelist capacity (defense in depth - ALWAYS ENABLED)
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// CRITICAL: Enable in both debug and release to prevent corruption accumulation
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// Reason: If C7 slips through magic validation, capacity limit prevents unbounded growth
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// Cost: 1 comparison (~1 cycle, predict-not-taken)
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// Benefit: Fail-safe against TLS SLL pollution from false positives
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uint32_t cap = (uint32_t)TINY_TLS_MAG_CAP;
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if (__builtin_expect(g_tls_sll_count[class_idx] >= cap, 0)) {
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return 0; // Route to slow path for spill (Front Gate will catch corruption)
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}
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// 3. Push base to TLS freelist (4 instructions, 5-7 cycles)
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// Must push base (block start) not user pointer!
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// Phase E1: ALL classes (C0-C7) have 1-byte header → base = ptr-1
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void* base = (char*)ptr - 1;
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// REVERT E3-2: Use Box TLS-SLL for all builds (testing hypothesis)
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// Hypothesis: Box TLS-SLL acts as verification layer, masking underlying bugs
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if (!tls_sll_push(class_idx, base, UINT32_MAX)) {
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// C7 rejected or capacity exceeded - route to slow path
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return 0;
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}
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return 1; // Success - handled in fast path
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}
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// ========== Free Entry Point ==========
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// Entry point for free() - tries fast path first, falls back to slow path
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//
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// Flow:
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// 1. Try ultra-fast free (header-based) → 95-99% hit rate
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// 2. Miss → Fallback to slow path → 1-5% (non-header, cache full)
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//
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// Performance:
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// - Fast path: 5-10 cycles (header read + TLS push)
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// - Slow path: 500+ cycles (SuperSlab lookup + validation)
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// - Weighted average: ~10-30 cycles (vs 500+ current)
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static inline void hak_free_fast_v2_entry(void* ptr) {
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// Try ultra-fast free (header-based)
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if (__builtin_expect(hak_tiny_free_fast_v2(ptr), 1)) {
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return; // Success - done in 5-10 cycles!
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}
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// Slow path: Non-header allocation or TLS cache full
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hak_tiny_free(ptr);
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}
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// ========== Performance Counters (Debug) ==========
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#if !HAKMEM_BUILD_RELEASE
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// Performance counters (TLS, lightweight)
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static __thread uint64_t g_free_v2_fast_hits = 0;
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static __thread uint64_t g_free_v2_slow_hits = 0;
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// Track fast path hit rate
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static inline void hak_free_v2_track_fast(void) {
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g_free_v2_fast_hits++;
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}
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static inline void hak_free_v2_track_slow(void) {
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g_free_v2_slow_hits++;
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}
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// Print stats at exit
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static void hak_free_v2_print_stats(void) __attribute__((destructor));
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static void hak_free_v2_print_stats(void) {
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uint64_t total = g_free_v2_fast_hits + g_free_v2_slow_hits;
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if (total == 0) return;
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double hit_rate = (double)g_free_v2_fast_hits / total * 100.0;
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fprintf(stderr, "[FREE_V2] Fast hits: %lu, Slow hits: %lu, Hit rate: %.2f%%\n",
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g_free_v2_fast_hits, g_free_v2_slow_hits, hit_rate);
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}
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#else
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// Release: No tracking overhead
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static inline void hak_free_v2_track_fast(void) {}
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static inline void hak_free_v2_track_slow(void) {}
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#endif
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// ========== Benchmark Comparison ==========
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//
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// Current (hak_tiny_free_superslab):
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// - 2x SuperSlab lookup: 200+ cycles
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// - Safety checks (O(n) duplicate scan): 100+ cycles
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// - Validation, atomics, diagnostics: 200+ cycles
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// - Total: 500+ cycles
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// - Throughput: 1.2M ops/s
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//
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// Phase 7 (hak_tiny_free_fast_v2):
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// - Header read: 2-3 cycles
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// - TLS push: 3-5 cycles
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// - Total: 5-10 cycles (100x faster!)
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// - Throughput: 40-60M ops/s (30-50x improvement)
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//
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// vs System malloc tcache:
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// - System: 10-15 cycles (3-4 instructions)
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// - HAKMEM: 5-10 cycles (3-5 instructions)
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// - Result: 70-110% of System speed (互角〜勝ち!)
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#endif // HAKMEM_TINY_HEADER_CLASSIDX
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