tools/perf/tests/workloads/datasym.c

Source file repositories/reference/linux-study-clean/tools/perf/tests/workloads/datasym.c

File Facts

System
Linux kernel
Corpus path
tools/perf/tests/workloads/datasym.c
Extension
.c
Size
1438 bytes
Lines
61
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

struct buf {
	char data1;
	char reserved[55];
	char data2;
} __attribute__((aligned(64)));

/* volatile to try to avoid the compiler seeing reserved as unused. */
static volatile struct buf workload_datasym_buf1 = {
	/* to have this in the data section */
	.reserved[0] = 1,
};

static volatile sig_atomic_t done;

static void sighandler(int sig __maybe_unused)
{
	done = 1;
}

static int datasym(int argc, const char **argv)
{
	int sec = 1;

	if (argc > 0)
		sec = atoi(argv[0]);

	signal(SIGINT, sighandler);
	signal(SIGALRM, sighandler);
	alarm(sec);

	while (!done) {
		workload_datasym_buf1.data1++;
		if (workload_datasym_buf1.data1 == 123) {
			/*
			 * Add some 'noise' in the loop to work around errata
			 * 1694299 on Arm N1.
			 *
			 * Bias exists in SPE sampling which can cause the load
			 * and store instructions to be skipped entirely. This
			 * comes and goes randomly depending on the offset the
			 * linker places the datasym loop at in the Perf binary.
			 * With an extra branch in the middle of the loop that
			 * isn't always taken, the instruction stream is no
			 * longer a continuous repeating pattern that interacts
			 * badly with the bias.
			 */
			workload_datasym_buf1.data1++;
		}
		workload_datasym_buf1.data2 += workload_datasym_buf1.data1;
	}
	return 0;
}

DEFINE_WORKLOAD(datasym);

Annotation

Implementation Notes