47 lines
1.8 KiB
C
47 lines
1.8 KiB
C
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// fastlane_direct_env_box.h - Phase 19-1: FastLane Direct Path ENV Control
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//
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// Goal: Remove wrapper layer overhead (30.79% of cycles) by calling core allocator directly
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// Strategy: Compile-time + runtime gate to bypass front_fastlane_try_*() wrapper
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//
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// Box Theory:
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// - Boundary: HAKMEM_FASTLANE_DIRECT=0/1 (default: 0, opt-in)
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// - Rollback: ENV=0 reverts to existing FastLane wrapper path
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// - Observability: perf stat shows instruction/branch reduction
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//
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// Expected Performance:
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// - Reduction: -17.5 instructions/op, -6.0 branches/op
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// - Impact: +10-15% throughput (remove 30% wrapper overhead)
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//
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// ENV Variables:
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// HAKMEM_FASTLANE_DIRECT=0/1 # Enable direct path (default: 0, research box)
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#pragma once
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#include <stdatomic.h>
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#include <stdlib.h>
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// ENV control: cached flag for fastlane_direct_enabled()
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// -1: uninitialized, 0: disabled, 1: enabled
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// NOTE: Must be a single global (not header-static) so bench_profile refresh can
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// update the same cache used by malloc/free wrappers.
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extern _Atomic int g_fastlane_direct_enabled;
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// Runtime check: Is FastLane Direct path enabled?
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// Returns: 1 if enabled, 0 if disabled
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// Hot path: Single atomic load (after first call)
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static inline int fastlane_direct_enabled(void) {
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int val = atomic_load_explicit(&g_fastlane_direct_enabled, memory_order_relaxed);
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if (__builtin_expect(val == -1, 0)) {
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// Cold path: Initialize from ENV
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const char* e = getenv("HAKMEM_FASTLANE_DIRECT");
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int enable = (e && *e && *e != '0') ? 1 : 0;
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atomic_store_explicit(&g_fastlane_direct_enabled, enable, memory_order_relaxed);
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return enable;
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}
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return val;
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}
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// Refresh from ENV: Called during benchmark ENV reloads
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// Allows runtime toggle without recompilation
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void fastlane_direct_env_refresh_from_env(void);
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