foxhunt/simd_debug.rs

#!/usr/bin/env cargo +nightly -Zscript
//! Debug SIMD performance issues by testing different components

use std::arch::is_x86_feature_detected;
use std::time::Instant;

#[cfg(target_arch = "x86_64")]
mod simd_tests {
    use std::arch::x86_64::*;
    use std::time::Instant;

    // Test 1: Pure SIMD arithmetic (no memory operations)
    pub unsafe fn test_pure_simd_arithmetic(iterations: usize) -> std::time::Duration {
        let start = Instant::now();
        
        let a = _mm256_set1_pd(1.5);
        let b = _mm256_set1_pd(2.5);
        let mut result = _mm256_setzero_pd();
        
        for _ in 0..iterations {
            result = _mm256_add_pd(result, _mm256_mul_pd(a, b));
        }
        
        // Prevent optimization from removing the loop
        let mut sum = [0.0; 4];
        _mm256_storeu_pd(sum.as_mut_ptr(), result);
        let _total: f64 = sum.iter().sum();
        
        start.elapsed()
    }

    // Test 2: SIMD with simple memory loads
    pub unsafe fn test_simd_memory_loads(data: &[f64], iterations: usize) -> std::time::Duration {
        let start = Instant::now();
        
        let mut sum = _mm256_setzero_pd();
        
        for _ in 0..iterations {
            let mut i = 0;
            while i + 4 <= data.len() {
                let vec = _mm256_loadu_pd(&data[i]);
                sum = _mm256_add_pd(sum, vec);
                i += 4;
            }
        }
        
        // Prevent optimization
        let mut result = [0.0; 4];
        _mm256_storeu_pd(result.as_mut_ptr(), sum);
        let _total: f64 = result.iter().sum();
        
        start.elapsed()
    }

    // Test 3: Complex SIMD with prefetching (similar to foxhunt implementation)
    pub unsafe fn test_complex_simd_with_prefetch(prices: &[f64], volumes: &[f64], iterations: usize) -> std::time::Duration {
        let start = Instant::now();
        
        for _ in 0..iterations {
            let mut price_volume_sum = _mm256_setzero_pd();
            let mut volume_sum = _mm256_setzero_pd();
            let len = prices.len();
            let mut i = 0;

            // Process 4 elements at a time with prefetching
            while i + 16 <= len {
                // Prefetch next cache lines (like foxhunt code)
                _mm_prefetch(
                    prices.as_ptr().add(i + 16) as *const i8,
                    _MM_HINT_T0,
                );
                _mm_prefetch(
                    volumes.as_ptr().add(i + 16) as *const i8,
                    _MM_HINT_T0,
                );

                // Process in groups of 4
                for j in (i..i + 16).step_by(4) {
                    let price_vec = _mm256_loadu_pd(&prices[j]);
                    let volume_vec = _mm256_loadu_pd(&volumes[j]);
                    
                    let pv_vec = _mm256_mul_pd(price_vec, volume_vec);
                    price_volume_sum = _mm256_add_pd(price_volume_sum, pv_vec);
                    volume_sum = _mm256_add_pd(volume_sum, volume_vec);
                }
                
                i += 16;
            }

            // Extract results (like foxhunt code)
            let sum_high_low = _mm256_hadd_pd(price_volume_sum, price_volume_sum);
            let sum_128 = _mm256_extractf128_pd(sum_high_low, 1);
            let sum_64 = _mm_add_pd(_mm256_castpd256_pd128(sum_high_low), sum_128);
            let _pv_sum = _mm_cvtsd_f64(sum_64);

            let vol_sum_high_low = _mm256_hadd_pd(volume_sum, volume_sum);
            let vol_sum_128 = _mm256_extractf128_pd(vol_sum_high_low, 1);
            let vol_sum_64 = _mm_add_pd(_mm256_castpd256_pd128(vol_sum_high_low), vol_sum_128);
            let _vol_sum = _mm_cvtsd_f64(vol_sum_64);
        }
        
        start.elapsed()
    }

    // Test 4: Aligned memory allocation (like AlignedPrices)
    pub unsafe fn test_aligned_allocation(size: usize, iterations: usize) -> std::time::Duration {
        #[repr(align(32))]
        struct AlignedData {
            data: Vec<f64>,
        }

        let start = Instant::now();
        
        for _ in 0..iterations {
            let mut aligned = AlignedData {
                data: Vec::with_capacity(size),
            };
            aligned.data.resize(size, 1.0);
            
            // Verify alignment
            let _is_aligned = (aligned.data.as_ptr() as usize) % 32 == 0;
            
            // Simple SIMD operation on aligned data
            let mut sum = _mm256_setzero_pd();
            let mut i = 0;
            while i + 4 <= aligned.data.len() {
                let vec = _mm256_loadu_pd(&aligned.data[i]);
                sum = _mm256_add_pd(sum, vec);
                i += 4;
            }
            
            // Prevent optimization
            let mut result = [0.0; 4];
            _mm256_storeu_pd(result.as_mut_ptr(), sum);
            let _total: f64 = result.iter().sum();
        }
        
        start.elapsed()
    }
}

fn scalar_baseline(data: &[f64], iterations: usize) -> std::time::Duration {
    let start = Instant::now();
    
    for _ in 0..iterations {
        let mut sum = 0.0;
        for &val in data {
            sum += val;
        }
        let _result = sum;
    }
    
    start.elapsed()
}

fn scalar_vwap(prices: &[f64], volumes: &[f64], iterations: usize) -> std::time::Duration {
    let start = Instant::now();
    
    for _ in 0..iterations {
        let mut total_pv = 0.0;
        let mut total_vol = 0.0;
        
        for i in 0..prices.len() {
            total_pv += prices[i] * volumes[i];
            total_vol += volumes[i];
        }
        
        let _vwap = if total_vol > 0.0 { total_pv / total_vol } else { 0.0 };
    }
    
    start.elapsed()
}

fn generate_test_data(size: usize) -> (Vec<f64>, Vec<f64>) {
    let mut prices = Vec::with_capacity(size);
    let mut volumes = Vec::with_capacity(size);

    for i in 0..size {
        prices.push(100.0 + (i as f64 * 0.01));
        volumes.push(1000.0 + (i as f64 * 10.0));
    }

    (prices, volumes)
}

fn main() {
    println!("🔬 SIMD Performance Debug Analysis");
    println!("=================================");
    
    if !is_x86_feature_detected!("avx2") {
        println!("❌ AVX2 not available");
        return;
    }
    println!("✅ AVX2 detected\n");

    let size = 10000;
    let iterations = 1000;
    let (prices, volumes) = generate_test_data(size);

    println!("Testing with {} elements, {} iterations\n", size, iterations);

    // Test 1: Pure SIMD arithmetic
    #[cfg(target_arch = "x86_64")]
    unsafe {
        let simd_time = simd_tests::test_pure_simd_arithmetic(iterations * 100);
        println!("📊 Test 1 - Pure SIMD Arithmetic:");
        println!("  Time: {:?}", simd_time);
        println!("  (This should be very fast - pure computation)\n");
    }

    // Test 2: Simple SIMD vs Scalar memory operations
    let scalar_time = scalar_baseline(&prices, iterations);
    
    #[cfg(target_arch = "x86_64")]
    unsafe {
        let simd_time = simd_tests::test_simd_memory_loads(&prices, iterations);
        let speedup = scalar_time.as_nanos() as f64 / simd_time.as_nanos() as f64;
        
        println!("📊 Test 2 - Simple Memory Loads:");
        println!("  Scalar: {:?}", scalar_time);
        println!("  SIMD:   {:?}", simd_time);
        println!("  Speedup: {:.2}x", speedup);
        
        if speedup < 1.0 {
            println!("  🚨 REGRESSION: SIMD {:.2}x slower!", 1.0 / speedup);
        } else if speedup > 2.0 {
            println!("  ✅ GOOD: Above 2x speedup");
        } else {
            println!("  ⚠️  SUBOPTIMAL: Below 2x speedup");
        }
        println!();
    }

    // Test 3: Complex SIMD with prefetching (foxhunt style)
    let scalar_vwap_time = scalar_vwap(&prices, &volumes, iterations);
    
    #[cfg(target_arch = "x86_64")]
    unsafe {
        let complex_simd_time = simd_tests::test_complex_simd_with_prefetch(&prices, &volumes, iterations);
        let speedup = scalar_vwap_time.as_nanos() as f64 / complex_simd_time.as_nanos() as f64;
        
        println!("📊 Test 3 - Complex SIMD (Foxhunt style):");
        println!("  Scalar: {:?}", scalar_vwap_time);
        println!("  SIMD:   {:?}", complex_simd_time);
        println!("  Speedup: {:.2}x", speedup);
        
        if speedup < 1.0 {
            println!("  🚨 REGRESSION: SIMD {:.2}x slower!", 1.0 / speedup);
            println!("  💡 Issue likely in complex implementation");
        } else if speedup > 2.0 {
            println!("  ✅ GOOD: Above 2x speedup");
        } else {
            println!("  ⚠️  SUBOPTIMAL: Below 2x speedup");
        }
        println!();
    }

    // Test 4: Aligned memory allocation overhead
    #[cfg(target_arch = "x86_64")]
    unsafe {
        let aligned_time = simd_tests::test_aligned_allocation(size, iterations / 10); // Fewer iterations due to allocation cost
        
        println!("📊 Test 4 - Aligned Memory Allocation:");
        println!("  Time: {:?}", aligned_time);
        println!("  (High time indicates allocation overhead)\n");
    }

    println!("🔍 Analysis Summary:");
    println!("- Test 1 shows pure SIMD computation performance");
    println!("- Test 2 shows SIMD vs scalar for simple operations");
    println!("- Test 3 replicates the foxhunt SIMD complexity");
    println!("- Test 4 shows alignment/allocation overhead");
    println!("\nIf Test 2 is good but Test 3 is bad, the issue is in complex implementation.");
    println!("If Test 4 is very slow, alignment code has problems.");
}