SilverSight/experiments/epyc_oisc_cacheline_bench.c

/*
 * epyc_oisc_cacheline_bench.c
 *
 * Cache-line-granular OISC benchmark for EPYC 9645 Turin.
 *
 * Three models, each building on the last:
 *
 *   1. WORD-SUBLEQ  — traditional subleq on int16 words (baseline)
 *   2. CL-SUBLEQ    — subleq on 64-byte cache lines via AVX-512 aligned load/store
 *   3. PCIE-TLP     — each OISC instr = 64-byte PCIe TLP from a virtio-style
 *                     ring buffer; measures raw TLP throughput
 *
 * The model: a cache-native OISC pipeline hooks PCIe signal hooks (TLP
 * transactions) as its instruction fetch / memory access path.  Every
 * instruction is one or more 64-byte cache-line reads/writes — exactly
 * what PCIe Gen5 x16 delivers as a single transaction.
 *
 * Build:
 *   gcc -march=znver5 -O3 -flto -mavx512f -mavx512bw \
 *       epyc_oisc_cacheline_bench.c -o oisc_cl_bench
 *
 * Run:
 *   perf stat -e cycles,instructions,cache-references,cache-misses,\
 *       L1-dcache-load-misses,LLC-load-misses,branch-misses \
 *       ./oisc_cl_bench
 */

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <time.h>
#include <stdalign.h>
#include <immintrin.h>

/* ================================================================
 * Common constants
 * ================================================================ */
#define CL_SIZE  64          /* x86 cache line */
#define CL_WORDS (CL_SIZE / sizeof(int16_t))   /* 32 int16 per cache line */
#define N_LINES  4096        /* 4096 cache lines = 256 KB workspace */
#define MEM_SIZE (N_LINES * CL_SIZE)
#define HALT     0x8000

/* ================================================================
 * 1. WORD-SUBLEQ (baseline)
 *    mem[dst] -= mem[src]; if mem[dst] <= 0 → pc = next; else pc += 3
 *    Word-aligned, no padding.
 * ================================================================ */
static int64_t bench_word_subleq(int16_t *mem, int pc, int N) {
    int16_t src, dst, next;
    int64_t iters = 0;
    int cnt = 0;

    while (cnt < N) {
        src = mem[pc];
        dst = mem[pc + 1];
        next = mem[pc + 2];
        if (next == HALT) break;
        mem[dst] -= mem[src];
        pc = (mem[dst] <= 0) ? next : pc + 3;
        iters++;
        cnt++;
    }
    return iters;
}

/* Build a word-SUBLEQ program that executes ~N iterations.
 * Returns pc of first instruction. */
static int build_word_prog(int16_t *mem, int N, int *out_pc) {
    memset(mem, 0, MEM_SIZE);

    /* Layout:
     *   line 0: constants  (zero=0, neg1=-1, one=1, limit=N/64)
     *   line 1: program (src,dst,next triples)
     *   line 2+: workspace
     */
    mem[0]  = 0;              /* zero addr */
    mem[1]  = -1;             /* neg1 */
    mem[2]  = 1;              /* one */
    mem[3]  = N;              /* limit */

    int cnt_addr  = 64;       /* counter at word 64 */
    int tmp_addr  = 65;       /* temp at word 65 */
    mem[cnt_addr] = 0;
    mem[tmp_addr] = 0;

    /*
     * Loop:
     *   I0: cnt -= neg1   (cnt++)
     *   I1: tmp -= cnt     (tmp = N - cnt)
     *   I2: branch if tmp <= 0
     */

    int pc = 100;  /* program at word 100 */
    *out_pc = pc;

    /* I0: cnt += 1 (cnt -= neg1, where neg1 = -1) */
    mem[pc]     = 1;      /* src = addr 1 = neg1 */
    mem[pc + 1] = cnt_addr;
    mem[pc + 2] = -1;     /* fall through */
    pc += 3;

    /* I1: tmp = N - cnt (tmp -= cnt, tmp starts = N at line 0) */
    mem[pc]     = cnt_addr;
    mem[pc + 1] = tmp_addr;
    mem[pc + 2] = pc + 3; /* fall through to I2 */
    pc += 3;

    /* I2: if tmp <= 0 → halt; else → loop */
    /* tmp <= 0 means we ran N iterations */
    mem[pc]     = 0;      /* src = zero (no-op for tmp) */
    mem[pc + 1] = tmp_addr;
    mem[pc + 2] = *out_pc;  /* loop back */
    pc += 3;

    /* HALT */
    mem[pc]     = 0;
    mem[pc + 1] = 0;
    mem[pc + 2] = HALT;

    return pc + 3;  /* total words used */
}

/* ================================================================
 * 2. CL-SUBLEQ (cache-line granular)
 *
 * Each "word" in this variant is a 64-byte cache line.  The SUBLEQ
 * instruction becomes:
 *
 *   line[dst] := line[dst] − line[src]   (elementwise, via AVX-512)
 *   if all(line[dst]) <= 0 → pc = next; else pc += 3
 *
 * "All zeros" is checked as: the first int16 of a cache line ≤ 0.
 * For a real pipeline, this would be a SIMD compare + mask test.
 * ================================================================ */
typedef int64_t cacheline_t[CL_WORDS] __attribute__((aligned(64)));

static inline void cl_sub(cacheline_t *a, cacheline_t *b) {
    /* b[] -= a[] using AVX-512 */
    __m512i va = _mm512_load_si512(a);
    __m512i vb = _mm512_load_si512(b);
    __m512i vr = _mm512_sub_epi16(vb, va);
    _mm512_store_si512(b, vr);
}

static inline int cl_is_nonpositive(cacheline_t *b) {
    /* Return 1 if first element <= 0 (proxy for "all zero") */
    return (*b)[0] <= 0;
}

static int64_t bench_cl_subleq(cacheline_t *mem, int pc, int N) {
    int16_t src, dst, next;
    int64_t iters = 0;
    int cnt = 0;

    while (cnt < N) {
        /* The "program" is still stored as int16 triples in line 0 */
        src  = ((int16_t *)mem)[pc];
        dst  = ((int16_t *)mem)[pc + 1];
        next = ((int16_t *)mem)[pc + 2];
        if (next == HALT) break;

        cl_sub(&mem[src], &mem[dst]);

        pc = cl_is_nonpositive(&mem[dst]) ? next : pc + 3;
        iters++;
        cnt++;
    }
    return iters;
}

/* ================================================================
 * 3. PCIE-TLP model
 *
 * Simulates PCIe Transaction Layer Packets as the instruction transport.
 * Each TLP = 64 bytes (one cache line):
 *   [src_line:16] [dst_line:16] [next_line:16] [flags:16] [payload: 56 B pad]
 *
 * The OISC engine reads TLPs from a "RX ring" (pre-allocated buffer),
 * executes the SUBLEQ on cache lines, and writes result TLPs to a
 * "TX ring."
 *
 * Metric: TLPs processed per second = cache lines / sec.
 * At PCIe Gen5 x16 (64 GT/s, 128B/130B encoding) = ~63 GB/s raw.
 * Each TLP read+write = 2 × 64B = 128B per instruction.
 * Theoretical max: ~492 M TLPs/sec per PCIe Gen5 x16 lane pair.
 *
 * This benchmark measures the software-side bottleneck.
 * ================================================================ */
typedef struct __attribute__((packed, aligned(64))) {
    uint16_t src_line;
    uint16_t dst_line;
    uint16_t next_line;
    uint16_t flags;
    uint8_t  pad[56];     /* fill to 64 B */
} PcieTlp;

/* Generate a batch of TLPs in a ring buffer */
static int generate_tlps(PcieTlp *ring, int count, int src_line,
                          int dst_line, int next_line) {
    for (int i = 0; i < count; i++) {
        ring[i].src_line  = src_line;
        ring[i].dst_line  = dst_line;
        ring[i].next_line = next_line;
        ring[i].flags     = 0;
        memset(ring[i].pad, 0, 56);
    }
    return count;
}

/* Execute a TLP stream against a cache-line memory, as PCIe RX→process→TX */
static int64_t bench_pcie_tlp(PcieTlp *rx_ring, int n_tlps,
                               cacheline_t *mem) {
    int64_t processed = 0;

    for (int i = 0; i < n_tlps; i++) {
        PcieTlp *tlp = &rx_ring[i];

        /* SUBLEQ on cache lines */
        cl_sub(&mem[tlp->src_line], &mem[tlp->dst_line]);

        /* "Write-back" — mark TLP as processed (simulates TX completion) */
        tlp->flags = 1;
        processed++;
    }
    return processed;
}

/* ================================================================
 * Timing helper
 * ================================================================ */
static double now_sec(void) {
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    return ts.tv_sec + ts.tv_nsec * 1e-9;
}

/* ================================================================
 * Main
 * ================================================================ */
int main(void) {
    printf("=== EPYC 9645 Turin — Cache-Line OISC Benchmark ===\n\n");

    /* ---------- 1. WORD SUBLEQ ---------- */
    printf("--- 1. WORD-SUBLEQ (baseline) ---\n");
    int16_t *word_mem = aligned_alloc(64, MEM_SIZE);
    int word_pc;
    build_word_prog(word_mem, 10000000, &word_pc);

    double t0 = now_sec();
    int64_t wi = bench_word_subleq(word_mem, word_pc, 10000000);
    double t1 = now_sec();
    double ws = wi / (t1 - t0) / 1e6;
    printf("  %ld iter in %.4f sec = %.2f M instr/sec\n",
           (long)wi, t1 - t0, ws);
    printf("  Words touched/sec: %.2f M\n", ws * 6);  /* 6 word accesses per instr */
    free(word_mem);

    /* ---------- 2. CL SUBLEQ ---------- */
    printf("\n--- 2. CL-SUBLEQ (cache-line granular, AVX-512) ---\n");
    cacheline_t *cl_mem = aligned_alloc(64, MEM_SIZE);

    /* Build program in cl_mem[0] as int16 triples */
    int cl_pc;
    build_word_prog((int16_t *)cl_mem, 10000000, &cl_pc);

    /* Warmup */
    bench_cl_subleq(cl_mem, cl_pc, 1000);
    build_word_prog((int16_t *)cl_mem, 10000000, &cl_pc);

    t0 = now_sec();
    int64_t ci = bench_cl_subleq(cl_mem, cl_pc, 1000000);
    t1 = now_sec();
    double cs = ci / (t1 - t0) / 1e6;
    printf("  %ld iter in %.4f sec = %.2f M instr/sec\n",
           (long)ci, t1 - t0, cs);
    printf("  Cache lines touched/sec: %.2f M\n", cs * 2);
    free(cl_mem);

    /* ---------- 3. PCIE TLP ---------- */
    printf("\n--- 3. PCIE-TLP MODEL (cache-line TLP stream) ---\n");

    int n_tlps = 100000;
    PcieTlp *rx_ring = aligned_alloc(64, n_tlps * sizeof(PcieTlp));
    cacheline_t *tlp_mem = aligned_alloc(64, MEM_SIZE);

    /* Set up: zero memory, generate TLP stream */
    memset(tlp_mem, 0, MEM_SIZE);
    generate_tlps(rx_ring, n_tlps, 2, 3, HALT);
    /* line 2 = zero, line 3 = zero.  cl_sub(zero, zero) = no-op. */

    /* Warmup */
    bench_pcie_tlp(rx_ring, 1000, tlp_mem);

    t0 = now_sec();
    int64_t pi = bench_pcie_tlp(rx_ring, n_tlps, tlp_mem);
    t1 = now_sec();
    double ps = pi / (t1 - t0) / 1e6;
    printf("  %ld TLPs in %.4f sec = %.2f M TLPs/sec\n",
           (long)pi, t1 - t0, ps);
    printf("  PCIe BW equivalent: %.2f GB/s  (2 × 64B per TLP)\n",
           ps * 128.0 / 1000.0);
    /* Each TLP = 64B read + 64B write = 128B */
    free(rx_ring);
    free(tlp_mem);

    /* ---------- SUMMARY ---------- */
    printf("\n=== SUMMARY ===\n");
    printf("  %-30s %12.2f M ops/sec\n", "WORD-SUBLEQ", ws);
    printf("  %-30s %12.2f M ops/sec\n", "CL-SUBLEQ (AVX-512)", cs);
    printf("  %-30s %12.2f M ops/sec\n", "PCIE-TLP (cache line)", ps);
    printf("\n  TLP → PCIe Gen5 x16 raw:  ~63 GB/s\n");
    printf("  TLP → PCIe Gen5 x8 raw:   ~31 GB/s\n");
    printf("  TLP → PCIe Gen4 x16 raw:  ~31 GB/s\n");

    return 0;
}