Add madvise_bounce

Signed-off-by: Andy Lutomirski <luto@kernel.org>

2 files changed, 87 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 82382aa..c31760f 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ SIMPLE_C_TARGETS := dump-vsyscall context_switch_latency kernel_pf user_visible_
 SIMPLE_CC_TARGETS := evil-clock-test
 
 SPLIT_C_TARGETS := dump-vdso dump-vvar syscall_exit_regs dump_all_pmcs ntflag sysret_ss_attrs
-SPLIT_CC_TARGETS := timing_test test_vsyscall test_vdso_parser
+SPLIT_CC_TARGETS := timing_test test_vsyscall test_vdso_parser madvise_bounce
 
 ALL_TARGETS := $(SIMPLE_C_TARGETS) $(SIMPLE_CC_TARGETS) $(SPLIT_C_TARGETS:%=%_64) $(SPLIT_CC_TARGETS:%=%_64) $(SPLIT_C_TARGETS:%=%_32) $(SPLIT_CC_TARGETS:%=%_32) syscall32_from_64 segregs
 
diff --git a/madvise_bounce.cc b/madvise_bounce.cc
new file mode 100644
index 0000000..1888fc7
--- /dev/null
+++ b/madvise_bounce.cc
@@ -0,0 +1,86 @@
+#define __STDC_FORMAT_MACROS
+
+#include <sys/time.h>
+#include <time.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <dlfcn.h>
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include <atomic>
+#include <signal.h>
+#include <pthread.h>
+#include <err.h>
+#include <sys/mman.h>
+
+void describe_clock(const char *name, int id)
+{
+	struct timespec res;
+	int ret = clock_getres(id, &res);
+	if (ret < 0) {
+		printf("  %d (%s)  [failed to query resolution]\n",
+		       id, name);
+	} else {
+		printf("  %d (%s)  resolution = %" PRIu64 ".%09u\n",
+		       id, name,
+		       (uint64_t)res.tv_sec, (unsigned)res.tv_nsec);
+	}
+}
+
+int main(int argc, char **argv)
+{
+	if (argc < 2) {
+		printf("Usage: %s <iters>\n", argv[0]);
+
+		return 1;
+	}
+
+	cpu_set_t cpuset;
+	CPU_ZERO(&cpuset);
+	int cpu = 0;
+
+	long loop_mult = 1;
+	char *loop_arg = strdup(argv[1]);
+	size_t loop_arg_len = strlen(loop_arg);
+	if (loop_arg_len && loop_arg[loop_arg_len-1] == 'k') {
+		loop_mult = 1000;
+		loop_arg[loop_arg_len-1] = '\0';
+	} else if (loop_arg_len && loop_arg[loop_arg_len-1] == 'M') {
+		loop_mult = 1000000;
+		loop_arg[loop_arg_len-1] = '\0';
+	}
+	size_t loops = (size_t)atol(argv[1]) * loop_mult;
+	free(loop_arg);
+
+	char *buf = (char *)mmap(0, 4096, PROT_READ|PROT_WRITE,
+				 MAP_ANONYMOUS | MAP_PRIVATE | MAP_POPULATE,
+				 -1, 0);
+	if (buf == MAP_FAILED)
+		err(1, "mmap");
+
+	timespec start;
+	clock_gettime(CLOCK_MONOTONIC, &start);
+
+	for (size_t i = 0; i < loops; ++i) {
+		madvise(buf, 4096, MADV_DONTNEED);
+		buf[0] = 1;
+
+		cpu = !cpu;
+		CPU_SET(cpu, &cpuset);
+		if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
+			err(1, "sched_setaffinity");
+		CPU_CLR(cpu, &cpuset);
+	}
+
+	timespec end;
+	clock_gettime(CLOCK_MONOTONIC, &end);
+	unsigned long long duration = (end.tv_nsec - start.tv_nsec) + 1000000000ULL * (end.tv_sec - start.tv_sec);
+	printf("%ld loops in %.5fs = %.2f nsec / loop\n",
+	       (long)loops, float(duration) * 1e-9,
+	       float(duration) / loops);
+	if (duration == 0)
+		printf("[WARN]\tThe apparent elapsed time was exactly 0.  You have precision issues.\n");
+	return 0;
+}