Pacing timer (#563)

* Add --pacing-timer option to allow tuning of -b timers.
These control the granularity of the timer and hence burstiness
of iperf3's sends.  The default is 1ms (1000), which is the default
starting with iperf 3.2.  Follow-on to the commit in #460.

* Update manpage and release notes for --pacing-timer.

RELEASE_NOTES

@@ -9,9 +9,10 @@
     correct test durations for all protocols (#560, #238).
 
   * Application-level bandwidth pacing (--bandwidth option) is now
-    checked every millisecond, instead of of every tenth of a second,
-    to provide smoother traffic behavior when using application
-    pacing.  (#460)
+    checked every millisecond by default, instead of of every tenth of
+    a second, to provide smoother traffic behavior when using
+    application pacing.  (#460) The pacing can be tuned via the use of
+    the --pacing-timer option.
 
   * A new --dscp option allows specifying the DSCP value to be used
     for outgoing packets (#508).  The TOS byte value is now printed in

src/iperf.h

@@ -116,6 +116,7 @@ struct iperf_settings
     int       blksize;              /* size of read/writes (-l) */
     uint64_t  rate;                 /* target data rate for application pacing*/
     uint64_t  fqrate;               /* target data rate for FQ pacing*/
+    int	      pacing_timer;	    /* pacing timer in microseconds */
     int       burst;                /* packets per burst */
     int       mss;                  /* for TCP MSS */
     int       ttl;                  /* IP TTL option */

src/iperf3.1

@@ -124,6 +124,16 @@ This bandwidth limit is implemented internally inside iperf3, and is
 available on all platforms.
 Compare with the \--fq-rate flag.
 .TP
+.BR --pacing-timer " \fIn\fR[KMG]"
+set pacing timer interval in microseconds (default 1000 microseconds,
+or 1 ms).
+This controls iperf3's internal pacing timer for the -b/--bandwidth
+option.
+The timer fires at the interval set by this parameter.
+Smaller values of the pacing timer parameter smooth out the traffic
+emitted by iperf3, but potentially at the cost of performance due to
+more frequent timer processing.
+.TP
 .BR --fq-rate " \fIn\fR[KM]"
 Set a rate to be used with fair-queueing based socket-level pacing,
 in bits per second.

src/iperf_api.c

@@ -681,6 +681,7 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
     {"authorized-users-path", required_argument, NULL, OPT_SERVER_AUTHORIZED_USERS},
 #endif /* HAVE_SSL */
 	{"fq-rate", required_argument, NULL, OPT_FQ_RATE},
+	{"pacing-timer", required_argument, NULL, OPT_PACING_TIMER},
         {"debug", no_argument, NULL, 'd'},
         {"help", no_argument, NULL, 'h'},
         {NULL, 0, NULL, 0}
@@ -1012,7 +1013,11 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
             test->server_authorized_users = strdup(optarg);
             break;
 #endif /* HAVE_SSL */
-            case 'h':
+	    case OPT_PACING_TIMER:
+		test->settings->pacing_timer = unit_atoi(optarg);
+		client_flag = 1;
+		break;
+	    case 'h':
 		usage_long(stdout);
 		exit(0);
             default:
@@ -1298,7 +1303,7 @@ iperf_create_send_timers(struct iperf_test * test)
 	if (test->settings->rate != 0) {
 	    cd.p = sp;
 	    /* (Repeat every millisecond - arbitrary value to provide smooth pacing.) */
-	    sp->send_timer = tmr_create((struct timeval*) 0, send_timer_proc, cd, 1000L, 1);
+	    sp->send_timer = tmr_create((struct timeval*) 0, send_timer_proc, cd, test->settings->pacing_timer, 1);
 	    if (sp->send_timer == NULL) {
 		i_errno = IEINITTEST;
 		return -1;
@@ -1460,6 +1465,8 @@ send_parameters(struct iperf_test *test)
 	    cJSON_AddNumberToObject(j, "bandwidth", test->settings->rate);
 	if (test->settings->fqrate)
 	    cJSON_AddNumberToObject(j, "fqrate", test->settings->fqrate);
+	if (test->settings->pacing_timer)
+	    cJSON_AddNumberToObject(j, "pacing_timer", test->settings->pacing_timer);
 	if (test->settings->burst)
 	    cJSON_AddNumberToObject(j, "burst", test->settings->burst);
 	if (test->settings->tos)
@@ -1545,6 +1552,8 @@ get_parameters(struct iperf_test *test)
 	    test->settings->rate = j_p->valueint;
 	if ((j_p = cJSON_GetObjectItem(j, "fqrate")) != NULL)
 	    test->settings->fqrate = j_p->valueint;
+	if ((j_p = cJSON_GetObjectItem(j, "pacing_timer")) != NULL)
+	    test->settings->pacing_timer = j_p->valueint;
 	if ((j_p = cJSON_GetObjectItem(j, "burst")) != NULL)
 	    test->settings->burst = j_p->valueint;
 	if ((j_p = cJSON_GetObjectItem(j, "TOS")) != NULL)
@@ -2037,6 +2046,7 @@ iperf_defaults(struct iperf_test *testp)
     testp->settings->blksize = DEFAULT_TCP_BLKSIZE;
     testp->settings->rate = 0;
     testp->settings->fqrate = 0;
+    testp->settings->pacing_timer = 1000;
     testp->settings->burst = 0;
     testp->settings->mss = 0;
     testp->settings->bytes = 0;

src/iperf_api.h

@@ -58,6 +58,7 @@ struct iperf_stream;
 #define OPT_CLIENT_RSA_PUBLIC_KEY 13
 #define OPT_SERVER_RSA_PRIVATE_KEY 14
 #define OPT_SERVER_AUTHORIZED_USERS 15
+#define OPT_PACING_TIMER 16
 
 /* states */
 #define TEST_START 1

src/iperf_locale.c

@@ -134,6 +134,7 @@ const char usage_longstr[] = "Usage: iperf3 [-s|-c host] [options]\n"
                            "  -b, --bandwidth #[KMG][/#] target bandwidth in bits/sec (0 for unlimited)\n"
                            "                            (default %d Mbit/sec for UDP, unlimited for TCP)\n"
                            "                            (optional slash and packet count for burst mode)\n"
+			   "  --pacing-timer #[KMG]     set the timing for pacing, in microseconds (default 1000)\n"
 #if defined(HAVE_SO_MAX_PACING_RATE)
                            "  --fq-rate #[KMG]          enable fair-queuing based socket pacing in\n"
 			   "                            bits/sec (Linux only)\n"