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// SPDX-License-Identifier: BSD-3-Clause
/*
* p2_regs - register-usage / launch-bounds variants.
*
* Three kernels cover different register-allocation regimes while staying
* exact (unsigned wraparound is well defined; no floating point):
*
* regs_lo __launch_bounds__(256, 4) - strongly capped register use
* (<= 64 registers/thread on the 65536-register file)
* regs_hi 64 independent accumulators x 128 update steps - high
* register pressure (the compiler may spill; correctness is
* unaffected by where the values live)
* regs_bounds __launch_bounds__(128, 4) - a second occupancy target with a
* different block size
*
* Every kernel writes one unsigned per element of a 1024-element buffer; the
* CPU mirrors the exact integer expressions, so the buffer must match
* element for element. INFO lines report the compiler's register counts and
* the queried occupancy (informational; ignored by the A/B comparison).
*
* Device memory: one 4 KB unsigned buffer (1 page).
*/
#include "common.h"
#define RG_N 1024
__global__ void __launch_bounds__(256, 4) regs_lo(unsigned *out, int n)
{
int i = blockIdx.x * blockDim.x + threadIdx.x;
if (i < n)
out[i] = ((unsigned)i ^ 0x5a5au) + 3u;
}
__global__ void regs_hi(unsigned *out, int n, unsigned seed)
{
int i = blockIdx.x * blockDim.x + threadIdx.x;
unsigned acc[64];
unsigned s = 0;
if (i >= n)
return;
#pragma unroll
for (int k = 0; k < 64; k++)
acc[k] = seed + (unsigned)k * ((unsigned)i + 1u);
for (int t = 0; t < 128; t++) {
#pragma unroll
for (int k = 0; k < 64; k++)
acc[k] = acc[k] * 2654435761u + ((unsigned)t ^ (unsigned)k);
}
#pragma unroll
for (int k = 0; k < 64; k++)
s += acc[k];
out[i] = s;
}
__global__ void __launch_bounds__(128, 4) regs_bounds(unsigned *out, int n)
{
int i = blockIdx.x * blockDim.x + threadIdx.x;
if (i < n)
out[i] = (unsigned)(i * 5) + 7u;
}
static unsigned cpu_lo(int i)
{
return ((unsigned)i ^ 0x5a5au) + 3u;
}
static unsigned cpu_hi(int i, unsigned seed)
{
unsigned acc[64];
unsigned s = 0;
for (int k = 0; k < 64; k++)
acc[k] = seed + (unsigned)k * ((unsigned)i + 1u);
for (int t = 0; t < 128; t++)
for (int k = 0; k < 64; k++)
acc[k] = acc[k] * 2654435761u + ((unsigned)t ^ (unsigned)k);
for (int k = 0; k < 64; k++)
s += acc[k];
return s;
}
static unsigned cpu_bounds(int i)
{
return (unsigned)(i * 5) + 7u;
}
template <typename T>
static void info_attrs(const char *name, T fn, int block)
{
cudaFuncAttributes a;
int occ = -1;
if (cudaFuncGetAttributes(&a, fn) != cudaSuccess)
return;
(void)cudaOccupancyMaxActiveBlocksPerMultiprocessor(&occ, fn, block, 0);
printf("INFO regs %s numregs=%d maxthreads=%d occ_blocks_per_sm=%d\n",
name, a.numRegs, a.maxThreadsPerBlock, occ);
}
int main(int argc, char **argv)
{
static const unsigned seed = 0x12345678u;
int bad = 0;
if (p2_emit_mode(argc, argv)) {
printf("RESULT regs kernel=lo n=%d bad=0\n", RG_N);
printf("RESULT regs kernel=hi n=%d bad=0\n", RG_N);
printf("RESULT regs kernel=bounds n=%d bad=0\n", RG_N);
printf("RESULT regs kernels=3 bad=0\n");
return p2_status(0);
}
p2_device_info();
unsigned *d_out = NULL;
unsigned *got = (unsigned *)malloc(sizeof(unsigned) * RG_N);
if (!got)
return 1;
P2_CHECK(cudaMalloc(&d_out, sizeof(unsigned) * RG_N));
regs_lo<<<(RG_N + 255) / 256, 256>>>(d_out, RG_N);
P2_CHECK(cudaGetLastError());
P2_CHECK(cudaDeviceSynchronize());
P2_CHECK(cudaMemcpy(got, d_out, sizeof(unsigned) * RG_N,
cudaMemcpyDeviceToHost));
{
int sbad = 0;
for (int i = 0; i < RG_N; i++)
if (got[i] != cpu_lo(i))
sbad++;
printf("RESULT regs kernel=lo n=%d bad=%d\n", RG_N, sbad);
bad += sbad;
}
regs_hi<<<(RG_N + 255) / 256, 256>>>(d_out, RG_N, seed);
P2_CHECK(cudaGetLastError());
P2_CHECK(cudaDeviceSynchronize());
P2_CHECK(cudaMemcpy(got, d_out, sizeof(unsigned) * RG_N,
cudaMemcpyDeviceToHost));
{
int sbad = 0;
for (int i = 0; i < RG_N; i++)
if (got[i] != cpu_hi(i, seed))
sbad++;
printf("RESULT regs kernel=hi n=%d bad=%d\n", RG_N, sbad);
bad += sbad;
}
regs_bounds<<<(RG_N + 127) / 128, 128>>>(d_out, RG_N);
P2_CHECK(cudaGetLastError());
P2_CHECK(cudaDeviceSynchronize());
P2_CHECK(cudaMemcpy(got, d_out, sizeof(unsigned) * RG_N,
cudaMemcpyDeviceToHost));
{
int sbad = 0;
for (int i = 0; i < RG_N; i++)
if (got[i] != cpu_bounds(i))
sbad++;
printf("RESULT regs kernel=bounds n=%d bad=%d\n", RG_N, sbad);
bad += sbad;
}
info_attrs("lo", regs_lo, 256);
info_attrs("hi", regs_hi, 256);
info_attrs("bounds", regs_bounds, 128);
printf("RESULT regs kernels=3 bad=%d\n", bad);
cudaFree(d_out);
free(got);
return p2_status(bad);
}
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