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SubjectRe: [PATCH 3/3] utrace-based ftrace "process" engine, v2
Hi -

On Sat, Mar 21, 2009 at 04:45:01PM +0100, Ingo Molnar wrote:
> [...]
> To me personally there are two big direct usability issues with
> SystemTap:
> 1) It relies on DEBUG_INFO for any reasonable level of utility.
> Yes, it will limp along otherwise as well, but most of the
> actual novel capabilities depend on debuginfo. Which is an
> acceptable constraint for enterprise usage where kernels are
> switched every few months and having a debuginfo package is not
> a big issue. Not acceptable for upstream kernel development.

In my own limited kernel-building experience, I find the debuginfo
data conveniently and instantly available after every "make". Can you
elaborate how is it harder for you to incidentally make it than for
someone to download it?

> It also puts way too trust into the compiler generating 1GB+ of
> debuginfo correctly. I want to be able to rely on tools all the
> time and thus i want tools to have some really simple and
> predictable foundations.

Well, the data has to come from *somewhere*. We know several
shortcomings (and have staff working on gcc debuginfo improvements),
but there is little alternative. If not from the compiler, where are
you going to get detailed type/structure layouts? Stack slot to
variable mappings? Statement-level PC addresses? Unwind data?

> 2) It's not upstream and folks using it seem to insist on not
> having it upstream ;-) This 'distance' to upstream seems to have
> grown during the past few years - instead of shrinking. [...]

Considering our upstream-bound assistance with foundation technologies
like markers, tracepoints, kprobes, utrace, and several other bits,
this does not seem entirely fair.

> If these fundamental problems are addressed then i'd even argue for
> the totality of SystemTap to be aimed upstreamed (including the
> scripting language, etc.), [...]

If consensus on this were plausible, we could seriously discuss it.

But I don't buy the package-deal that utrace must not attempt merging
on its own merits, just because it makes systemtap (as it is today)
useful to more people.

- FChE

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