netstacklat: Add ebpf-exporter config

Add a YAML configuration that ebpf-exporter can use to convert the BPF
maps to Prometheus metrics. Convert the histogram map for each hook
into the corresponding Prometheus histogram.

Also update the README to explain how to use netstacklat together with
ebpf-exporter.

Signed-off-by: Simon Sundberg <[email protected]>

Author: simosund

netstacklat/README.md

@@ -33,4 +33,26 @@ sudo bpftrace -e '
 The eBPF part of the tool (`netstacklat.bpf.c`) is designed to be
 compatible with
 [ebpf_exporter](https://github.com/cloudflare/ebpf_exporter), so that
-the data can easily be exported to Prometheus.
+the data can easily be exported to Prometheus. The easiest way to use
+netstacklat together with ebpf-exporter is simply to point it to this
+directory, i.e.
+```console
+$ ebpf_exporter --config.dir=<path>/bpf-examples/netstacklat --config.names=netstacklat
+```
+
+Alternatively, you can copy over the files to ebpf-exporter's example
+repository.
+```console
+$ cp netstacklat.{bpf.c,h,yaml} -t <path>/ebpf_exporter/examples/
+# Fix up some header includes (e.g. "vmlinux_local.h" -> <vmlinux.h>
+$ make -C <path>/ebpf_exporter/examples build
+$ ebpf_exporter --config.dir=<path>/ebpf_exporter/examples --config.names
+```
+
+Note that when using together with ebpf-exporter, some of the
+functionality handled by netstacklat's userspace program will not be
+available. This includes setting the `TAI_OFFSET` constant in
+`netstacklat.bpf.c` to match your system's TAI offset (you can do this
+manually instead), and enabling RX timestamping by the kernel (see the
+`enable_sw_rx_tstamps()` function in `netstacklat.c` for an example of
+how to do this).

netstacklat/netstacklat.yaml

@@ -0,0 +1,35 @@
+metrics:
+  histograms:
+    - name: netstack_latency_tcp_v4_do_rcv_seconds
+      help: Netstack latency up to the tcp_v4_do_rcv() function
+      bucket_type: exp2
+      bucket_min: 0
+      bucket_max: 30
+      bucket_multiplier: 0.000000001 # nanoseconds to seconds
+      labels:
+        - name: bucket
+          size: 4
+          decoders:
+            - name: uint
+    - name: netstack_latency_tcp_data_queue_seconds
+      help: Netstack latency up to the tcp_data_queue() function
+      bucket_type: exp2
+      bucket_min: 0
+      bucket_max: 30
+      bucket_multiplier: 0.000000001 # nanoseconds to seconds
+      labels:
+        - name: bucket
+          size: 4
+          decoders:
+            - name: uint
+    - name: netstack_latency_udp_queue_rcv_seconds
+      help: Netstack latency up to the udp_queue_rcv_one_skb() function
+      bucket_type: exp2
+      bucket_min: 0
+      bucket_max: 30
+      bucket_multiplier: 0.000000001 # nanoseconds to seconds
+      labels:
+        - name: bucket
+          size: 4
+          decoders:
+            - name: uint