Re: user-space probes -- plan B from outer space

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

prasadav wrote:

> [...]  Well another approach is similar to Ptrace actions you have
> predefined handlers that some one can activate through a new
> systemcall. [...] 

A fixed pool of predefined handlers seem like an antithesis of
systemtap.  Did you have some user interface in mind for these?

> >   user.process(233).statement(0xfeedface)
> >   user("fche").process("/bin/vi").function("*init*")
>
> In my opinion user space probes is most useful in the case of server
> class kind of complicated programs which are usually long living,
> [...]  there is not much value with system wide tracing instead we
> should focus on process specific tracing. [...]

There is no contradiction here.  System-wide probing can be
accomplished by a collection of process-specific probes.

> [...] I am not sure i see the value of process("process name")
> syntax if our focus is process specific tracing.

It would be one way of identifying present or future processes to
probe.  For processes that do not yet exist, what other scheme do you
have in mind?

> I am not sure i see lot of value of this solution compared to a gdb
> batch job, but for bit better performance than the heavy weight gdb.
> [...]

How would this gdb batch job alternative work?  Are you intending to
compare the expressity of systemtap script with gdb macros?

> >Q: Is it worth it to try?  Is there a better way?
> >A: You tell me.
>
> Not really unless we can't come up with a simple enough of solution
> that lets handlers run in the kernel which gives the performance
> that we need [...]

Sure - that is why I called it "plan B": something to consider if
"plan A" does not come to fruition.

- FChE