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// Copyright 2025 Joshua Bakita
// taskset-like utility for the GPU
#define _GNU_SOURCE // For program_invocation_name
#include <argp.h>
#include <errno.h>
#include <error.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <unistd.h>
#include <cuda.h> // To help with getting GPC info
#include "libsmctrl.h"
const char* maintainer = "<jbakita@cs.unc.edu>";
const char* version = "nvtaskset 2025.03";
const char* desc = "taskset-like utility for NVIDIA GPUs.";
const struct argp_option opts[] = {
{0}
};
unsigned __int128 strtou128(const char *nptr, char **endptr, int base) {
unsigned __int128 result = 0;
if (base != 16)
error(1, EINVAL, "Internal error");
// Skip a "0x" prefix. Safe due to early evaluation
if (*nptr == '0' && (*(nptr + 1) == 'x' || *(nptr + 1) == 'X'))
nptr += 2;
// Until hitting an invalid character
while (1) {
if (*nptr >= 'a' && *nptr <= 'f')
result = result << 4 | (*nptr - 'a' + 10);
else if (*nptr >= 'A' && *nptr <= 'F')
result = result << 4 | (*nptr - 'A' + 10);
else if (*nptr >= '0' && *nptr <= '9')
result = result << 4 | (*nptr - '0');
else
break;
nptr++;
}
if (endptr)
*endptr = (char*)nptr;
return result;
}
void libsmctrl_get_gpc_info_ext_easy(uint32_t* num_gpcs, uint128_t** masks, int gpu_id) {
int res;
CUcontext ctx;
// XXX: Copied from libsmctrl_test_gpc_info
// Tell CUDA to use PCI device id ordering (to match nvdebug)
putenv((char*)"CUDA_DEVICE_ORDER=PCI_BUS_ID");
// A CUDA context is required before reading the topology information
if ((res = cuInit(0))) {
const char* name;
cuGetErrorName(res, &name);
fprintf(stderr, "%s: Unable to initialize CUDA, error %s\n", program_invocation_name, name);
exit(1);
}
if ((res = cuCtxCreate(&ctx, 0, 0))) {
const char* name;
cuGetErrorName(res, &name);
fprintf(stderr, "%s: Unable to create a CUDA context, error %s\n", program_invocation_name, name);
exit(1);
}
// Pull topology information from libsmctrl
if ((res = libsmctrl_get_gpc_info_ext(num_gpcs, masks, gpu_id)) != 0) {
error(0, res, "libsmctrl_get_gpc_info() failed");
if (res == ENOENT)
fprintf(stderr, "%s: Is the nvdebug kernel module loaded?\n", program_invocation_name);
if (res == EIO)
fprintf(stderr, "%s: Is the GPU powered on, i.e., is there an active context?\n", program_invocation_name);
exit(1);
}
// Not copied
unsetenv("CUDA_DEVICE_ORDER");
}
int main(int argc, char **argv) {
if (argc < 3) {
fprintf(stderr, "Usage: %s -p <hex mask> <pid>\n", argv[0]);
fprintf(stderr, " %s <hex mask> <command> <argument...>\n", argv[0]);
fprintf(stderr, " %s --gpc-list <gpc list> <command> <argument...>\n", argv[0]);
fprintf(stderr, " <hex mask> has a bit set for each TPC to be enabled\n");
return 1;
}
// TODO: Use a proper argument parser
if (strcmp("-p", argv[1]) == 0) { // Setting mask on running task
char *end;
pid_t target_pid = strtoul(argv[2], &end, 10);
// strtoul stores a pointer to the first invalid character in `end`
if (*end != '\0') {
fprintf(stderr, "Invalid character \"%c\" in PID argument.\n", *end);
return 1;
}
unsigned __int128 mask = strtou128(argv[3], &end, 16);
if (*end != '\0') {
fprintf(stderr, "Invalid character \"%c\" in mask argument.\n", *end);
return 1;
}
// The shared memory lookup key is the lower 16-bits of the PID | "sm"
key_t shm_key = target_pid << 16 | (int)'s' << 8 | (int) 'm';
// Get a handle to the 128-bit shared memory region
int shmid = shmget(shm_key, 16, 0);
if (shmid == -1)
error(1, errno, "Unable to find control region for PID %d", target_pid);
// Open the shared memory region
unsigned __int128 *supreme_mask = shmat(shmid, NULL, 0);
if (supreme_mask == (void*)-1)
error(1, errno, "Unable to open control region for PID %d", target_pid);
// Write the requested mask into the shared memory region
*supreme_mask = mask;
} else { // Starting a new task with a mask
// TODO: Check other locations for nvidia-cuda-mps-control if its not on the path
// TODO: Use dup2() to redirect MPS startup messages
int ret = system("echo -n | nvidia-cuda-mps-control");
if (ret == -1)
error(1, errno, "Unable to run subshell to check MPS status");
if (ret != 0) { // Control deamon not yet started
fprintf(stderr, "nvtaskset: MPS control deamon does not appear to be running. Automatically starting...\n");
ret = system("nvidia-cuda-mps-control -d");
if (ret == -1)
error(1, errno, "Unable to run subshell to start MPS");
if (ret == 1) {
fprintf(stderr, "nvtaskset: Error starting MPS control deamon. Terminating...\n");
return 1;
}
fprintf(stderr, "nvtaskset: Done. Use \"echo quit | nvidia-cuda-mps-control\" to terminate it later as desired.\n");
}
// Tell loader to initialize libsmctrl.so first
// TODO: Append, rather than overwrite LD_PRELOAD
setenv("LD_PRELOAD", "./libsmctrl.so", 1);
// Explictly set the number of channels, otherwise CUDA will only use two
// (see paper for why that causes problems)
setenv("CUDA_DEVICE_MAX_CONNECTIONS", "8", 1);
// Check if a mask, or a list of GPCs is being provided
if (strcmp(argv[1], "--gpc-list") == 0) {
// TODO: Support the full syntax that taskset supports
// We just support X,Y,Z for now
uint32_t num_gpcs = 0;
uint128_t* masks = NULL;
// TODO: Allow specifying GPU ID, rather than assuming 0!
libsmctrl_get_gpc_info_ext_easy(&num_gpcs, &masks, 0);
uint128_t mask = 0;
int range_start_gpc = -1;
char* start = argv[2];
int len = strlen(argv[2]);
// TODO: Handle invalid input cleanly.
// Convert comma-seperated GPC list into a mask
for (int i = 0; i < len + 1; i++) {
if (argv[2][i] == ',' || argv[2][i] == '\0') {
argv[2][i] = '\0';
int gpc = atoi(start);
if (gpc > num_gpcs - 1) {
fprintf(stderr, "Invalid GPC ID '%s'!\n", start);
return 1;
}
// Handle ranges
if (range_start_gpc != -1) {
if (range_start_gpc >= gpc) {
fprintf(stderr, "Invalid GPC range!\n");
return 1;
}
while (range_start_gpc <= gpc) {
//printf("gpc %i\n", range_start_gpc);
mask |= masks[range_start_gpc];
range_start_gpc++;
}
range_start_gpc = -1;
} else {
//printf("gpc %i\n", gpc);
mask |= masks[gpc];
}
start = argv[2] + i + 1;
}
// Range start
if (argv[2][i] == '-') {
argv[2][i] = '\0';
range_start_gpc = atoi(start);
start = argv[2] + i + 1;
}
}
// Convert to string, prefix with ~, and set env var
char mask_str[32+3+1]; // 32 hexits, "~0x", and '\0'
snprintf(mask_str, 36, "~0x%lx%016lx", (uint64_t)(mask >> 64), (uint64_t)mask);
//printf("nvtaskset: Using mask string %s\n", mask_str);
setenv("LIBSMCTRL_MASK", mask_str, 1);
// Start task
execvp(argv[3], argv+3);
error(1, errno, "Unable to launch task '%s'", argv[3]);
} else {
// Tell libsmctrl what mask to use
char* mask = malloc(strlen(argv[1]) + 2);
mask[0] = '~'; // Make an enable mask
strcpy(mask+1, argv[1]);
setenv("LIBSMCTRL_MASK", mask, 1);
free(mask); // setenv() made a copy
// Start task
execvp(argv[2], argv+2);
error(1, errno, "Unable to launch task '%s'", argv[2]);
}
}
fprintf(stderr, "Invalid arguments\n");
return 1;
}
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