When trying to solve complex performance issues, a kernel trace can be the last resort: capture everything and try to understand what is going on. With LTTng, that would go like that:
lttng create lttng enable-event -k -a lttng start ...wait for the problem to appear... lttng stop lttng destroy
Once this is done, depending on how long the capture is, there are probably a lot of events in the resulting trace (~50.000 events per second on my mostly idle laptop), now it is time to make sense of it !
This post is a first in a serie to present the LTTng analyses scripts. In this one, we will try to solve an unusual I/O latency issue.