Re: systemtap/pcp integration

[fche at redhat dot com (Frank Ch. Eigler)]

Hi, David -

> Here's a small update on the prototype systemtap/pcp integration work
> I'm doing. 

Thanks, what a great start.

> I've create a systemtap branch, called 'dsmith/mmv' that contains
> all my work. Basically this work allows systemtap to create 'mmv'
> memory mapped files.

(That's git://sourceware.org/git/systemtap.git branch dsmith/mmv.)

> [...] The code works for the attached script, but I'm sure it is
> quite fragile. Things like locking, error checking, documentation,
> etc. need to be done. [...]

Overall, are you happy with the general approach of reusing the exact
MMV format (and thus the PMDA)?

At one point I suggested reworking the earlier prototype so that the
bulk of the MMV format's emulation would be based on tapset script
code (and possibly more declarative / dynamic / safe) rather than C.
Have you come to any conclusions about the propriety of that?

How much post-initialization change can the MMV format tolerate, as
regarding indom contents or metric availability?  I assume such
metadata changes are synchronized with the PMDA via the generation
numbers.  Moving around contents of the mmap region as in
__stp_mmv_alloc_data_item sounds like it leaves the data inconsistent
during the process; does it need similar protection?

- FChE