pure getcpu() example

userland/linux/getcpu.c

@@ -0,0 +1,53 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#getcpu */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <sched.h> /* getcpu */
+#include <pthread.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+/* man getcpu says this exists since glibc 2.29, but I can't find it in Ubuntu 20.04 glibc 2.31 not even with locate
+ * (there is a hit under /usr/src/linux-headers-5.4.0-29/include/linux/getcpu.h but it only defines `struct getcpu_cache`
+ * and nothing else:
+ * https://stackoverflow.com/questions/23224607/how-do-i-include-linux-header-files-like-linux-getcpu-h
+ * Furthermore, there is already a prototype in sched.h, so we can't define our own either. */
+#if 0
+#include <linux/getcpu.h>
+#endif
+
+void* main_thread(void *arg) {
+    (void)arg;
+    unsigned cpu, numa;
+    getcpu(&cpu, &numa);
+    printf("%u %u\n", cpu, numa);
+    return NULL;
+}
+
+int main(int argc, char **argv) {
+    pthread_t *threads;
+    unsigned int nthreads, i;
+    if (argc > 1) {
+        nthreads = strtoll(argv[1], NULL, 0);
+    } else {
+        nthreads = 1;
+    }
+    threads = malloc(nthreads * sizeof(*threads));
+    for (i = 0; i < nthreads; ++i) {
+        assert(pthread_create(
+            &threads[i],
+            NULL,
+            main_thread,
+            NULL
+        ) == 0);
+    }
+    for (i = 0; i < nthreads; ++i) {
+        pthread_join(threads[i], NULL);
+    }
+    free(threads);
+    return EXIT_SUCCESS;
+}

userland/linux/sched_getaffinity.c

@@ -2,7 +2,7 @@
 
 #define _GNU_SOURCE
 #include <assert.h>
-#include <sched.h>
+#include <sched.h> /* sched_getaffinity */
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>

userland/linux/sched_getcpu.c

@@ -5,6 +5,7 @@
 #include <pthread.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <sched.h> /* sched_getcpu */
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>