Re: LTTng finds abnormally long APIC interrupt handler : 58.2 ms

[fche@redhat.com (Frank Ch. Eigler)]

Steven Rostedt <rostedt@goodmis.org> writes:

> [...]
>> It all holds in a small module. Having the ability to connect any marker
>> on any generic probe from the lttng marker interface has been very
>> useful to do all this. Actually, this module has to be built into the
>> kernel because ftrace does not permit breeing the trace_ops data
>> structure. :/
>
> I did this purposely. The reason is that there is no safe way to release
> the trace_ops, because you never know if something is in the function
> you pointed to. If you remove the module after that, it crashes.
>
> I've been thinking of exporting it, and make it so that once you 
> register something to the trace_ops, I'll up the module count, and never 
> let that module unload.

This issue will need some sort of resolution if systemtap is to be
able to hook up to ftrace.  Perhaps we could have a second/nested API
that suffers the costs of explicit reference counting, but does permit
dynamic attach and robust detach.


- FChE