Using trace fsslower
The trace fsslower gadget streams file operations (open, read, write and fsync) that are slower than a threshold.
On Kubernetes
In this guide you’ll deploy an example workload that performs some open(), read() write() and sync() calls and will trace which ones are slower than 1 ms.
Let’s start the gadget before running our workload:
$ kubectl gadget trace fsslower -f ext4 -m 1 -p mypod
K8S.NODE K8S.NAMESPACE K8S.POD K8S.CONTAINER PID COMM T BYTES OFFSET LAT FILE
With -f we’re indicating the type of filesystem we want to trace,
ext4 in this case. The -m parameter indicates the threshold, in this
case operations taking more than 1ms will be printed. -p indicates
that we only want to trace events coming from mypod.
The T column indicates the operation type, O for open, R for read,
W for write and F for fsync.
In another terminal, let’s create a pod that updates the apt-get cache and installs git.
$ kubectl run -it mypod --image ubuntu -- /bin/sh -c "apt-get update && apt-get install -y git"
...
We can see how fsslower shows the operations that are taking longer than 1ms:
$ kubectl gadget trace fsslower -f ext4 -m 1 -p mypod
K8S.NODE K8S.NAMESPACE K8S.POD K8S.CONTAINER PID COMM T BYTES OFFSET LAT FILE
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 2.66 perl-modules-5.30.list-new
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 1.49 libperl5.30:amd64.list-new
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 1.45 control
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 1.01 less.list-new
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 1.05 symbols
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 1.05 md5sums
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 1.16 control
ubuntu-hirsute default mypod mypod 579778 dpkg F 0 0 1.09 git.list-new
ubuntu-hirsute default mypod mypod 580362 dpkg F 0 0 1.16 tmp.i
ubuntu-hirsute default mypod mypod 580363 frontend F 0 0 1.50 templates.dat-new
ubuntu-hirsute default mypod mypod 582040 dpkg-trigger F 0 0 1.10 triggers
ubuntu-hirsute default mypod mypod 580382 frontend F 0 0 1.22 templates.dat-new
ubuntu-hirsute default mypod mypod 583411 dpkg F 0 0 2.25 perl-modules-5.30.list-new
ubuntu-hirsute default mypod mypod 583411 dpkg F 0 0 2.05 libperl5.30:amd64.list-new
ubuntu-hirsute default mypod mypod 583411 dpkg F 0 0 1.13 tmp.i
ubuntu-hirsute default mypod mypod 583411 dpkg F 0 0 1.26 updates
ubuntu-hirsute default mypod mypod 583411 dpkg F 0 0 1.22 md5sums
That’s all, let’s delete our example pod
$ kubectl delete pod mypod
With ig
Let’s start the gadget in a terminal:
$ sudo ig trace fsslower -f ext4 -m 1 -c test-trace-fsslower
RUNTIME.CONTAINERNAME PID COMM T BYTES OFFSET LAT FILE
Launch a container that will perform input/output operations:
$ docker run --name test-trace-fsslower -it --rm debian /bin/sh -c "apt-get update && apt-get install -y git"
Get:1 http://deb.debian.org/debian bullseye InRelease [116 kB]
Get:2 http://deb.debian.org/debian-security bullseye-security InRelease [48.4 kB]
...
0 added, 0 removed; done.
Running hooks in /etc/ca-certificates/update.d...
done.
The tool will list the I/O operations that were slower than 1ms:
$ sudo ig trace fsslower -f ext4 -m 1 -c test-trace-fsslower
RUNTIME.CONTAINERNAME PID COMM T BYTES OFFSET LAT FILE
test-trace-fsslower 35065 apt-get R 32771 0 7671 status
test-trace-fsslower 35303 apt-get R 5619 0 7434 extended_states
test-trace-fsslower 35312 dpkg-preconfigu F 922337203… 0 3586 #29920952
test-trace-fsslower 35312 dpkg-preconfigu F 922337203… 0 4239 #29920954
test-trace-fsslower 35315 dpkg F 922337203… 0 3774 control
test-trace-fsslower 35315 dpkg F 922337203… 0 3049 md5sums
test-trace-fsslower 35315 dpkg F 922337203… 0 3064 tmp.ci
test-trace-fsslower 35315 dpkg F 922337203… 0 2886 tmp.i
test-trace-fsslower 35315 dpkg F 922337203… 0 4173 updates
...