Revise FIB lookups per second benchmarking routines.

Add a LPS benchmark variant which introduces artificial dependencies
between successive lookups. While here, instead of writing the results
from the lookups to a huge array, add them to an accumulator, in a more
lightweight attempt at preventing the CPU's OOO machinery from
discarding the lookup results if they would be completely unused.

net.route.test.run_lps_rnd measures LPS throughput with independent
uniformly random keys

net.route.test.run_lps_seq measures LPS throughput with uniformly
random keys with artificial interdependencies
Reviewed by:	melifaro
MFC after:	7 days
Differential Revision: https://reviews.freebsd.org/D30096

(cherry picked from commit a43104e)

sys/tests/fib_lookup/fib_lookup.c

@@ -509,13 +509,13 @@ static int
 rnd_lps(SYSCTL_HANDLER_ARGS)
 {
 	struct epoch_tracker et;
-	struct in_addr *keys;
-	struct nhop_object **nhops;
-
+	struct in_addr key;
 	struct timespec ts_pre, ts_post;
 	uint64_t total_diff, lps;
-	int error;
+	uint32_t *keys;
+	uintptr_t acc = 0;
 	int count = 0;
+	int error;
 
 	error = sysctl_handle_int(oidp, &count, 0, req);
 	if (error != 0)
@@ -524,39 +524,51 @@ rnd_lps(SYSCTL_HANDLER_ARGS)
 		return (0);
 
 	keys = malloc(sizeof(*keys) * count, M_TEMP, M_NOWAIT);
-	nhops = malloc(sizeof(*nhops) * count, M_TEMP, M_NOWAIT);
-	if (keys == NULL || nhops == NULL) {
-		free(keys, M_TEMP);
-		free(nhops, M_TEMP);
+	if (keys == NULL)
 		return (ENOMEM);
-	}
 
 	printf("Preparing %d random keys...\n", count);
 	arc4random_buf(keys, sizeof(*keys) * count);
 	printf("Starting LPS test...\n");
 
 	NET_EPOCH_ENTER(et);
 	nanouptime(&ts_pre);
-	for (int i = 0; i < count; i++)
-		nhops[i] = fib4_lookup(RT_DEFAULT_FIB, keys[i], 0, NHR_NONE, 0);
+	switch (arg2) {
+	case 0:
+		for (int i = 0; i < count; i++) {
+			key.s_addr = keys[i] + acc;
+			acc += (uintptr_t) fib4_lookup(RT_DEFAULT_FIB, key, 0,
+			    NHR_NONE, 0);
+		}
+	case 1:
+		for (int i = 0; i < count; i++) {
+			key.s_addr = keys[i];
+			acc += (uintptr_t) fib4_lookup(RT_DEFAULT_FIB, key, 0,
+			    NHR_NONE, 0);
+		}
+	}
 	nanouptime(&ts_post);
 	NET_EPOCH_EXIT(et);
 
 	free(keys, M_TEMP);
-	free(nhops, M_TEMP);
 
 	total_diff = (ts_post.tv_sec - ts_pre.tv_sec) * 1000000000 +
-	    (ts_post.tv_nsec - ts_pre.tv_nsec);
+	    (ts_post.tv_nsec - ts_pre.tv_nsec) + (acc & 1);
 	lps = 1000000000ULL * count / total_diff;
 	printf("%d lookups in %zu nanoseconds, %lu.%06lu MLPS\n",
 	    count, total_diff, lps / 1000000, lps % 1000000);
 
 	return (0);
 }
-SYSCTL_PROC(_net_route_test, OID_AUTO, rnd_lps,
+SYSCTL_PROC(_net_route_test, OID_AUTO, run_lps_seq,
     CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
     0, 0, rnd_lps, "I",
-    "Measure lookups per second using uniformly random keys");
+    "Measure lookups per second, uniformly random keys, "
+    "artificial dependencies between lookups");
+SYSCTL_PROC(_net_route_test, OID_AUTO, run_lps_rnd,
+    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
+    0, 1, rnd_lps, "I",
+    "Measure lookups per second, uniformly random keys, independent lookups");
 
 static int
 test_fib_lookup_modevent(module_t mod, int type, void *unused)