[ltt-dev] [PATCH 1/3] systemtap: kernel marker tapset

[Stone, Joshua I]

Masami Hiramatsu wrote:
> Here is a patch which adds a tapset for kernel markers.
> this tapset supports lttng's kernel marker(+my cpuid patch) too.

This looks very nice!  It will be great to finally use markers for lower
overhead probing...

In the "Context" documentation, you tend to restate the event, but I'm
looking for a description of which process environment is active when
the event occurs.  For some events, it's not obvious which process I
would see if I checked pid(), execname(), etc.  For example, does
marker.process.fork fire in the parent or the child?  Does
marker.scheduler.switch fire from the previous or next task?

Eventually, we'll also want to push these to a higher namespace without
the marker prefix.  Users generally shouldn't care *how* an event is
captured; stap should just pick the best option available.  Something
like:

probe process.exit =
    marker.process.exit!, // markers
    process("*").end!, // utrace
    kernel.function("do_exit") // kprobe


Josh