tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1#include <linux/compiler.h>
2#include "../tests.h"
3
4typedef struct _buf {
5 char data1;
6 char reserved[55];
7 char data2;
8} buf __attribute__((aligned(64)));
9
10static buf buf1 = {
11 /* to have this in the data section */
12 .reserved[0] = 1,
13};
14
15static int datasym(int argc __maybe_unused, const char **argv __maybe_unused)
16{
17 for (;;) {
18 buf1.data1++;
19 if (buf1.data1 == 123) {
20 /*
21 * Add some 'noise' in the loop to work around errata
22 * 1694299 on Arm N1.
23 *
24 * Bias exists in SPE sampling which can cause the load
25 * and store instructions to be skipped entirely. This
26 * comes and goes randomly depending on the offset the
27 * linker places the datasym loop at in the Perf binary.
28 * With an extra branch in the middle of the loop that
29 * isn't always taken, the instruction stream is no
30 * longer a continuous repeating pattern that interacts
31 * badly with the bias.
32 */
33 buf1.data1++;
34 }
35 buf1.data2 += buf1.data1;
36 }
37 return 0;
38}
39
40DEFINE_WORKLOAD(datasym);