tc-policy: Monitor TXQ usage with bpftrace script

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

tc-policy/README.org

@@ -54,3 +54,21 @@ You can now use it in all perf tools, such as:
 #+end_src
 
 Afterwards run =perf script= and see results.
+
+** bpftrace
+
+It is also possible to monitor TXQ usage via a =bpftrace= script.
+ * see [[file:monitor_txq_usage.bt]].
+
+The main part of the script is:
+#+begin_src sh
+ tracepoint:net:net_dev_start_xmit {
+	$qm = args->queue_mapping;
+	$dev = str(args->name, 15);
+
+	@stat_txq_usage[$dev] = lhist($qm, 0,32,1);
+ }
+#+end_src
+
+Or as oneliner:
+ * =bpftrace -e 't:net:net_dev_start_xmit {@txq[str(args->name, 15)]=lhist(args->queue_mapping, 0,32,1)}'=

tc-policy/monitor_txq_usage.bt

@@ -0,0 +1,26 @@
+#!/usr/bin/bpftrace
+
+//BEGIN {
+//	printf("Monitor TXQ usage\n");
+//	printf(" - Remember: BPF set queue_mapping is one-less here (zero-indexed)\n");
+//}
+
+tracepoint:net:net_dev_start_xmit {
+	$qm = args->queue_mapping;
+	$dev = str(args->name, 15);
+
+	@stat_txq_usage[$dev] = lhist($qm, 0,32,1);
+}
+
+/* Periodically print stats */
+interval:s:3
+{
+	printf("\nPeriodic show stats - time: ");
+        time();
+	print(@stat_txq_usage);
+}
+
+/* Default bpftrace will print all remaining maps at END */
+//END {
+//	printf("END stats:\n");
+//}