fpu_preempt.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * Copyright 2015, Cyril Bur, IBM Corp.
  4 * Copyright 2023, Michael Ellerman, IBM Corp.
  5 *
  6 * This test attempts to see if the FPU registers change across preemption.
  7 * There is no way to be sure preemption happened so this test just uses many
  8 * threads and a long wait. As such, a successful test doesn't mean much but
  9 * a failure is bad.
 10 */
 11
 12#include <stdio.h>
 13#include <unistd.h>
 14#include <sys/syscall.h>
 15#include <sys/time.h>
 16#include <sys/types.h>
 17#include <sys/wait.h>
 18#include <stdlib.h>
 19#include <pthread.h>
 20
 21#include "utils.h"
 22#include "fpu.h"
 23
 24/* Time to wait for workers to get preempted (seconds) */
 25#define PREEMPT_TIME 60
 26/*
 27 * Factor by which to multiply number of online CPUs for total number of
 28 * worker threads
 29 */
 30#define THREAD_FACTOR 8
 31
 32
 33__thread double darray[32];
 34
 35int threads_starting;
 36int running;
 37
 38extern int preempt_fpu(double *darray, int *threads_starting, int *running);
 39
 40void *preempt_fpu_c(void *p)
 41{
 42	long rc;
 43
 44	srand(pthread_self());
 45	randomise_darray(darray, ARRAY_SIZE(darray));
 46	rc = preempt_fpu(darray, &threads_starting, &running);
 47
 48	return (void *)rc;
 49}
 50
 51int test_preempt_fpu(void)
 52{
 53	int i, rc, threads;
 54	pthread_t *tids;
 55
 56	threads = sysconf(_SC_NPROCESSORS_ONLN) * THREAD_FACTOR;
 57	tids = malloc((threads) * sizeof(pthread_t));
 58	FAIL_IF(!tids);
 59
 60	running = true;
 61	threads_starting = threads;
 62	for (i = 0; i < threads; i++) {
 63		rc = pthread_create(&tids[i], NULL, preempt_fpu_c, NULL);
 64		FAIL_IF(rc);
 65	}
 66
 67	setbuf(stdout, NULL);
 68	/* Not really necessary but nice to wait for every thread to start */
 69	printf("\tWaiting for all workers to start...");
 70	while(threads_starting)
 71		asm volatile("": : :"memory");
 72	printf("done\n");
 73
 74	printf("\tWaiting for %d seconds to let some workers get preempted...", PREEMPT_TIME);
 75	sleep(PREEMPT_TIME);
 76	printf("done\n");
 77
 78	printf("\tStopping workers...");
 79	/*
 80	 * Working are checking this value every loop. In preempt_fpu 'cmpwi r5,0; bne 2b'.
 81	 * r5 will have loaded the value of running.
 82	 */
 83	running = 0;
 84	for (i = 0; i < threads; i++) {
 85		void *rc_p;
 86		pthread_join(tids[i], &rc_p);
 87
 88		/*
 89		 * Harness will say the fail was here, look at why preempt_fpu
 90		 * returned
 91		 */
 92		if ((long) rc_p)
 93			printf("oops\n");
 94		FAIL_IF((long) rc_p);
 95	}
 96	printf("done\n");
 97
 98	free(tids);
 99	return 0;
100}
101
102int main(int argc, char *argv[])
103{
104	return test_harness(test_preempt_fpu, "fpu_preempt");
105}