From e72d30978936cd0f133ba1e429c707c61ee0ff90 Mon Sep 17 00:00:00 2001
From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Tue, 1 Feb 2022 11:56:32 +0100
Subject: [PATCH] tc-policy: Monitor TXQ usage with bpftrace script

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 tc-policy/README.org           | 18 ++++++++++++++++++
 tc-policy/monitor_txq_usage.bt | 26 ++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100755 tc-policy/monitor_txq_usage.bt

diff --git a/tc-policy/README.org b/tc-policy/README.org
index 308dbc9..e8aa5a2 100644
--- a/tc-policy/README.org
+++ b/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)}'=
diff --git a/tc-policy/monitor_txq_usage.bt b/tc-policy/monitor_txq_usage.bt
new file mode 100755
index 0000000..5192996
--- /dev/null
+++ b/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");
+//}