[PATCH] pktgen: nowait parameter.

[Rusty Russell <rusty@rustcorp.com.au>]

While trying to measure speed of virtio_net, I was getting hangs.
This is because we skb_orphan() but delay the tx interrupt
indefinitely (by number of slots).

With nowait, pktgen won't wait for the skb to be released.  This
introduces an error, but it's ok if count >> ringsize.

I updated the documentation, but it needs far more work (it
refers to pgset and an examples directory, none of which exist
in the kernel tree).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/Documentation/networking/pktgen.txt b/Documentation/networking/pktgen.txt
index 0dffc6e37902..48d86da74a39 100644
--- a/Documentation/networking/pktgen.txt
+++ b/Documentation/networking/pktgen.txt
@@ -41,10 +41,13 @@ NIC HW layer (which is bad for bufferbloat).
 One should be careful to conclude, that packets/descriptors in the HW
 TX ring cause delay.  Drivers usually delay cleaning up the
 ring-buffers (for various performance reasons), thus packets stalling
-the TX ring, might just be waiting for cleanup.
+the TX ring, might just be waiting for cleanup.  Writing the "nowait"
+parameter into /proc/net/pktgen/ethX will avoid waiting for cleanup of
+the final packets, introducing a slight error (tiny if the count of
+packets being sent is much greater than the ring size of the device).
 
-This cleanup issues is specifically the case, for the driver ixgbe
-(Intel 82599 chip).  This driver (ixgbe) combine TX+RX ring cleanups,
+Alternately, some drivers (eg ixgbe for the Intel 82599 chip) can
+have their cleanup interval changed.  ixgbe combines TX+RX ring cleanups,
 and the cleanup interval is affected by the ethtool --coalesce setting
 of parameter "rx-usecs".
 
@@ -303,6 +305,8 @@ flowlen
 rate
 ratep
 
+nowait
+
 References:
 ftp://robur.slu.se/pub/Linux/net-development/pktgen-testing/
 ftp://robur.slu.se/pub/Linux/net-development/pktgen-testing/examples/
diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 8b849ddfef2e..adc41f2b3bc7 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -290,6 +290,11 @@ struct pktgen_dev {
 				 * set clone_skb to 1024.
 				 */
 
+	bool no_wait;		/*
+				 * Don't wait for packet to be freed
+				 * by driver
+				 */
+
 	char dst_min[IP_NAME_SZ];	/* IP, ie 1.2.3.4 */
 	char dst_max[IP_NAME_SZ];	/* IP, ie 1.2.3.4 */
 	char src_min[IP_NAME_SZ];	/* IP, ie 1.2.3.4 */
@@ -679,6 +684,9 @@ static int pktgen_if_show(struct seq_file *seq, void *v)
 
 	seq_puts(seq, "\n");
 
+	if (pkt_dev->no_wait)
+		seq_puts(seq, "     nowait\n");
+
 	/* not really stopped, more like last-running-at */
 	stopped = pkt_dev->running ? ktime_get() : pkt_dev->stopped_at;
 	idle = pkt_dev->idle_acc;
@@ -1711,6 +1719,17 @@ static ssize_t pktgen_if_write(struct file *file,
 		return count;
 	}
 
+	if (!strcmp(name, "nowait")) {
+		len = num_arg(&user_buffer[i], 10, &value);
+		if (len < 0)
+			return len;
+
+		i += len;
+		pkt_dev->no_wait = value;
+		sprintf(pg_result, "OK: nowait=%u", pkt_dev->no_wait);
+		return count;
+	}
+
 	sprintf(pkt_dev->result, "No such parameter \"%s\"", name);
 	return -EINVAL;
 }
@@ -3373,7 +3392,8 @@ unlock:
 
 	/* If pkt_dev->count is zero, then run forever */
 	if ((pkt_dev->count != 0) && (pkt_dev->sofar >= pkt_dev->count)) {
-		pktgen_wait_for_skb(pkt_dev);
+		if (!pkt_dev->no_wait)
+			pktgen_wait_for_skb(pkt_dev);
 
 		/* Done with this */
 		pktgen_stop_device(pkt_dev);
@@ -3565,6 +3585,7 @@ static int pktgen_add_device(struct pktgen_thread *t, const char *ifname)
 	pkt_dev->svlan_cfi = 0;
 	pkt_dev->svlan_id = 0xffff;
 	pkt_dev->node = -1;
+	pkt_dev->no_wait = false;
 
 	err = pktgen_setup_dev(t->net, pkt_dev, ifname);
 	if (err)