Andrew Morton wrote:
Balbir Singh <[email protected]> wrote:
On Wed, Mar 29, 2006 at 09:03:14PM -0800, Andrew Morton wrote:
Shailabh Nagar <[email protected]> wrote:
Could you please include the following delay accounting patches
in -mm ?
I'm at a loss to evaluate the suitability of this work, really. I always
am when accounting patches come along.
There are various people and various groups working on various different
things and there appears to be no coordination and little commonality of
aims. I worry that picking one submission basically at random will provide
nothing which the other groups can work on to build up their feature.
On the other hand, we don't want to do nothing until some uber-grand
all-singing, all-dancing statistics-gathering infrastructure comes along.
So I'm a bit stuck. What I would like to see happen is that there be some
coordination between the various stakeholders, and some vague plan which
they're all happy with as a basis for the eventual grand solution.
We already have various bits and pieces of statistics gathering in the
kernel and it's already a bit ad-hoc. Adding more one-requirement-specific
accounting code won't improve that situation.
But then, I said all this a year or two ago and nothing much has happened
since then. It's not your fault, but it's a problem.
Yes, I agree it is a problem. We found it ourselves while developing
this patchset. BSD accounting had
some properties we liked (like availability of stats for a process after
it died) but the way to extend it or
get access to those stats while a process was alive wasn't all that
good. Similarly CSA had needs like ours
but not quite the same.
Our compromise solution, prompted by your comments on getting a
consensus for the use of a "statistics
connector" for all accounting stakeholders, was the taskstats interface,
as described by Balbir below.
But it is not the complete solution or an attempt to get some common
accounting infrastructure, true :-(
Perhaps a good starting point would be a one-page bullet-point-form
wishlist of all the accounting which people want to get out of the kernel,
and a description of what the kernel<->user interface should look like.
Right now, I don't think we even have a picture of that.
We need a statistics maintainer, too, to pull together the plan,
coordinate, push things forwards. The first step would be to identify the
stakeholders, come up with that page of bullet-points.
Then again, maybe the right thing to do is to keep adding low-impact
requirement-specific statistics patches as they come along.
Personally, this is the approach I favor with unification happening
piecewise, atleast as far as the
collection of statistics is concerned.
The interface for making stats available outside would seem to be more
in need of a unified
approach since we already have a profusion of export methods, some
legacy and some being
introduced by folks like us.
But if we're
going to do it that way, we need an up-front reason for doing so, and I
don't know what that would be.
See my problem?
One of the issues we have tried to address is the ability to provide some
form of a common ground for all the statistics to co-exist. Various methods
were discussed for exchanging data between kernel and user space, genetlink
was suggested often and the clear winner.
To that end, we have created a taskstats.c file. Any subsystem wanting
to add their statistics and sending it to user space can add their own
types by extending taskstats.c (changing the version number) and creating
their own types using genetlink. They will have to do the following
1. Add statistics gathering in their own subsystem
2. Add a type to taskstats.c, extend it and use data from (1) and send
it to user space.
The data from various subsystems can co-exist. I feel that this could serve as
the basic common infrastructure to begin with and refined later (depending on
the needs of other people).
Sounds fine to me, but I'm not a stakeholder.
Trolling back through lse-tech gives us:
pnotify:
Erik Jacobson <[email protected]>
CSA accounting/PAGG/JOB:
Jay Lan <[email protected]>
Limin Gu <[email protected]>
per-process IO statistics:
Levent Serinol <[email protected]>
ELSA:
Guillaume Thouvenin <[email protected]>
per-cpu time statistics:
Erich Focht <[email protected]>
Scalable statistics counters with /proc reporting:
Ravikiran G Thirumalai <[email protected]>
(Kiran feft IBM, but presumably the requirement lives on)
To this list we can also add
Microstate accounting
Peter Chubb <[email protected]>
I don't know if Peter is still interested in pursuing this or it
was rejected.
There was a long thread "A common layer for Accounting packages". Did it
come to a conclusion?
Unfortunately, not.
Anyway, if mostly everyone is mostly happy with what you propose then that
it good news.
It would seem like a good first step then, for me to contact the folks
above and see if they are able to
use the interface we're proposing and modify it if needed.
--Shailabh
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