generic, x86: add tests for prctl PR_GET_TSC and PR_SET_TSC
This patch adds three tests that test whether the PR_GET_TSC and
PR_SET_TSC commands have the desirable effect.
The tests check whether the control register is updated correctly
at context switches and try to discover bugs while enabling/disabling
the timestamp counter.
Signed-off-by: Erik Bosman <ejbosman@cs.vu.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/Documentation/prctl/disable-tsc-on-off-stress-test.c b/Documentation/prctl/disable-tsc-on-off-stress-test.c
new file mode 100644
index 0000000..1fcd9144
--- /dev/null
+++ b/Documentation/prctl/disable-tsc-on-off-stress-test.c
@@ -0,0 +1,95 @@
+/*
+ * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...)
+ *
+ * Tests if the control register is updated correctly
+ * when set with prctl()
+ *
+ * Warning: this test will cause a very high load for a few seconds
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+#include <inttypes.h>
+#include <wait.h>
+
+
+#include <sys/prctl.h>
+#include <linux/prctl.h>
+
+/* Get/set the process' ability to use the timestamp counter instruction */
+#ifndef PR_GET_TSC
+#define PR_GET_TSC 25
+#define PR_SET_TSC 26
+# define PR_TSC_ENABLE 1 /* allow the use of the timestamp counter */
+# define PR_TSC_SIGSEGV 2 /* throw a SIGSEGV instead of reading the TSC */
+#endif
+
+/* snippet from wikipedia :-) */
+
+uint64_t rdtsc() {
+uint32_t lo, hi;
+/* We cannot use "=A", since this would use %rax on x86_64 */
+__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
+return (uint64_t)hi << 32 | lo;
+}
+
+int should_segv = 0;
+
+void sigsegv_cb(int sig)
+{
+ if (!should_segv)
+ {
+ fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
+ exit(0);
+ }
+ if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
+ {
+ perror("prctl");
+ exit(0);
+ }
+ should_segv = 0;
+
+ rdtsc();
+}
+
+void task(void)
+{
+ signal(SIGSEGV, sigsegv_cb);
+ alarm(10);
+ for(;;)
+ {
+ rdtsc();
+ if (should_segv)
+ {
+ fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
+ exit(0);
+ }
+ if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
+ {
+ perror("prctl");
+ exit(0);
+ }
+ should_segv = 1;
+ }
+}
+
+
+int main(int argc, char **argv)
+{
+ int n_tasks = 100, i;
+
+ fprintf(stderr, "[No further output means we're allright]\n");
+
+ for (i=0; i<n_tasks; i++)
+ if (fork() == 0)
+ task();
+
+ for (i=0; i<n_tasks; i++)
+ wait(NULL);
+
+ exit(0);
+}
+