play a bit with the ARM PMU

userland/linux/perf_event_open.c

@@ -0,0 +1,67 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#perf-event-open
+ *
+ * Malloc n bytes as given from the command line.
+ */
+
+#include <asm/unistd.h>
+#include <linux/perf_event.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include <lkmc.h>
+
+static long
+perf_event_open(struct perf_event_attr *hw_event, pid_t pid,
+                int cpu, int group_fd, unsigned long flags)
+{
+    int ret;
+
+    ret = syscall(__NR_perf_event_open, hw_event, pid, cpu,
+                    group_fd, flags);
+    return ret;
+}
+
+int
+main(int argc, char **argv)
+{
+    struct perf_event_attr pe;
+    long long count;
+    int fd;
+
+    uint64_t n;
+    if (argc > 1) {
+        n = strtoll(argv[1], NULL, 0);
+    } else {
+        n = 100;
+    }
+
+    memset(&pe, 0, sizeof(struct perf_event_attr));
+    pe.type = PERF_TYPE_HARDWARE;
+    pe.size = sizeof(struct perf_event_attr);
+    pe.config = PERF_COUNT_HW_INSTRUCTIONS;
+    pe.disabled = 1;
+    pe.exclude_kernel = 1;
+    // Don't count hypervisor events.
+    pe.exclude_hv = 1;
+
+    fd = perf_event_open(&pe, 0, -1, -1, 0);
+    if (fd == -1) {
+        fprintf(stderr, "Error opening leader %llx\n", pe.config);
+        exit(EXIT_FAILURE);
+    }
+
+    ioctl(fd, PERF_EVENT_IOC_RESET, 0);
+    ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
+
+    lkmc_busy_loop(n, 1);
+
+    ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);
+    read(fd, &count, sizeof(long long));
+
+    printf("Used %lld instructions\n", count);
+
+    close(fd);
+}