datasym.c

 1#include <stdlib.h>
 2#include <signal.h>
 3#include <unistd.h>
 4#include <linux/compiler.h>
 5#include "../tests.h"
 6
 7typedef struct _buf {
 8	char data1;
 9	char reserved[55];
10	char data2;
11} buf __attribute__((aligned(64)));
12
13/* volatile to try to avoid the compiler seeing reserved as unused. */
14static volatile buf workload_datasym_buf1 = {
15	/* to have this in the data section */
16	.reserved[0] = 1,
17};
18
19static volatile sig_atomic_t done;
20
21static void sighandler(int sig __maybe_unused)
22{
23	done = 1;
24}
25
26static int datasym(int argc, const char **argv)
27{
28	int sec = 1;
29
30	if (argc > 0)
31		sec = atoi(argv[0]);
32
33	signal(SIGINT, sighandler);
34	signal(SIGALRM, sighandler);
35	alarm(sec);
36
37	while (!done) {
38		workload_datasym_buf1.data1++;
39		if (workload_datasym_buf1.data1 == 123) {
40			/*
41			 * Add some 'noise' in the loop to work around errata
42			 * 1694299 on Arm N1.
43			 *
44			 * Bias exists in SPE sampling which can cause the load
45			 * and store instructions to be skipped entirely. This
46			 * comes and goes randomly depending on the offset the
47			 * linker places the datasym loop at in the Perf binary.
48			 * With an extra branch in the middle of the loop that
49			 * isn't always taken, the instruction stream is no
50			 * longer a continuous repeating pattern that interacts
51			 * badly with the bias.
52			 */
53			workload_datasym_buf1.data1++;
54		}
55		workload_datasym_buf1.data2 += workload_datasym_buf1.data1;
56	}
57	return 0;
58}
59
60DEFINE_WORKLOAD(datasym);