Using top ebpf
The top ebpf gadget is used to visualize the usage and performance of eBPF programs.
On Kubernetes
This guide will let you run another gadget (we’re using top file in this example) and see its metrics
using top ebpf.
So first, start top ebpf in a terminal. You should see something like:
$ kubectl gadget top ebpf
K8S.NODE PROGID TYPE NAME PID COMM RUNTIME RUNCOUNT MAPMEMORY MAPCOUNT
minikube 503 Tracing ig_top_ebpf_it 573222 gadgettracerman 54.09µs 1069 12B 1
minikube 187 CGroupDevice 2.292µs 1 0B 0
minikube 13 CGroupSKB 0s 0 0B 0
...
The output should already contain the top ebpf gadget itself.
Now, in a second terminal, start top file on the gadget namespace to get some output.
$ kubectl gadget top file -n gadget
K8S.NODE K8S.NAMESPACE K8S.POD K8S.CONTAINER PID COMM READS WRITES R_KB W_KB T FILE
minikube gadget gadget-k2mvp gadget 575955 runc:[2:INIT] 1 0 0 0 R cap_last_cap
minikube gadget gadget-k2mvp gadget 575955 runc:[2:INIT] 2 0 8 0 R group
minikube gadget gadget-k2mvp gadget 575955 gadgettracerman 2 0 8 0 R UTC
...
While the top file gadget is still running, go back to the first terminal.
Some eBPF programs of type Kprobe should pop up, including their runtime and run count in the current interval
(default is 1s):
$ kubectl gadget top ebpf
K8S.NODE PROGID TYPE NAME PID COMM RUNTIME RUNCOUNT MAPMEMORY MAPCOUNT
minikube 506 Kprobe ig_topfile_rd_e 573222 gadgettracerman 824.589µs 2076 40.95MiB 4
minikube 505 Tracing ig_top_ebpf_it 573222 gadgettracerman 47.171µs 1103 12B 1
minikube 507 Kprobe ig_topfile_wr_e 573222 gadgettracerman 609.645µs 836 40.95MiB 4
minikube 187 CGroupDevice 4.417µs 2 0B 0
minikube 13 CGroupSKB 0s 0 0B 0
minikube 8 CGroupSKB 0s 0 0B 0
...
So in this case for example, in the past second vfs_write_entry has been called 647 times, which took 614.455µs.
The program references 4 maps that have a total maximum size of 40.953 MB (see below for more information on MapMemory).
If you want to get the cumulative runtime and run count of the eBPF programs starting from the beginning of the trace,
you can call the gadget with the custom-columns option and specify the cumulruntime and cumulruncount columns.
Combined with the --sort cumulruntime and --timeout 60 parameters, you can for example measure the time spent
over a minute:
$ kubectl-gadget top ebpf -o columns=k8s.node,progid,type,name,pid,comm,cumulruntime,cumulruncount --sort cumulruntime --timeout 60
K8S.NODE PROGID TYPE NAME PID COMM CUMULRUNTIME CUMULRUNCOUNT
minikube 509 Tracing ig_top_ebpf_it 573222 gadgettracerman 1.265693ms 15879
minikube 187 CGroupDevice 40.795µs 48
minikube 256 CGroupDevice 5.834µs 2
minikube 13 CGroupSKB 0s 0
minikube 7 CGroupSKB 0s 0
minikube 8 CGroupSKB 0s 0
...
With ig
Run any tool that uses eBPF, for instance,
iovisor/bcc execsnoop
: from BCC. Please note that it can be run on the host directly.
$ sudo ./execsnoop
PCOMM PID PPID RET ARGS
runc 167851 142428 0 /usr/bin/runc --version
docker-init 167857 142428 0 /usr/bin/docker-init --version
...
Start the top ebpf gadget in another terminal. It’ll show the programs installed by the tool above.
$ sudo ig top ebpf
PROGID TYPE NAME PID COMM RUNTIME RUNCOUNT MAPMEMORY MAPCOUNT
1102 Tracing ig_top_ebpf_it 167925 ig 299.054µs 5534 4KiB 1
1097 TracePoint tracepoint__sys 167850 execsnoop 25.055µs 2 75.48MiB 3
1099 TracePoint tracepoint__sys 167850 execsnoop 23.629µs 2 75.48MiB 4
A note about memory usage of maps
The shown value for MapMemory is read from /proc/<pid>/fdinfo/<map_id>.
This is the maximum size the map can have, but it doesn’t necessarily reflect its current memory allocation. Additionally, maps can
be used by more than one program and would account towards the MapMemory of all those programs.
Also note:
- BPF_MAP_TYPE_PERF_EVENT_ARRAY: value_size is not counting the ring buffers, but only their file descriptors (i.e. sizeof(int) = 4 bytes)
- BPF_MAP_TYPE_{HASH,ARRAY}_OF_MAPS: value_size is not counting the inner maps, but only their file descriptors (i.e. sizeof(int) = 4 bytes)
A note about CPU usage
There are two types of cpu usage metrics available in top ebpf gadget:
- TotalCPUUsage: It means all ebpf progs' share of the elapsed CPU time since the last update, expressed as a percentage of total CPU time. This value can be >100% because it summed up cpu time in all cpu cores, similar to linux
top. - PerCPUUsage: This value is
TotalCPUUsage / CPUCoresandCPUCoresis the number of cpu cores in a node. PerCPUUsage will be always be <=100%. When using ebpf top gadget to check cpu usage for many nodes, it’s suggested to use PerCPUUsage.
To show them, you can run the gadget with percpu and totalcpu specified in -o columns option.