Re: [Patch 0/8] per-task delay accounting

[Balbir Singh <balbir@in.ibm.com>]

On Wed, Mar 29, 2006 at 09:03:14PM -0800, Andrew Morton wrote:
> Shailabh Nagar <nagar@watson.ibm.com> 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.
> 
> 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.  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).

Thoughts?

Balbir
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