linux-kernel - Re: [patch 0/4] Linux Kernel Markers

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Date:	Wed, 11 Jul 2007 17:43:20 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	akpm@...ux-foundation.org, Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 0/4] Linux Kernel Markers

* Frank Ch. Eigler (fche@...hat.com) wrote:
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> writes:
> 
> > This updated version of the Linux Kernel Markers mostly adds a unique 16 bits
> > per marker ID and a per-probe marker group. [...]
> 

Hello,

> Could you motivate this part better?  It is not covered in the
> documentation patch.
> 
> It seems to be a way of having a marker handling (callback) module
> give alternate names/ids to markers.  If so, why, considering that
> there is already a private void* callback parameter available to pass
> data back to itself through?
> 

The original reason was to get rid of a supplementary kmalloc() for each
active marker. However, I just noticed that I could pack my private data
in a slab cache, which makes the problem go away. I am therefore
removing IDs and groups from the markers.. they don't really belong to
this low-level infrastructure anyway, so this is all better.

> Also, what if different marker handling modules want to set different
> id/group numbers on the same set of markers?
> 

The way I see things now is to provide the simplest way to do the job,
without over-design. Clearly, putting the IDs and groups there was not
the best idea. I also think it will be up to a "tee" callback module to
implement a list of handlers (notifiers). However, supporting such a
list of handlers should not be a requirement for the low-level markers,
since has a significant performance impact which can be unwanted in the
common case (only one probe connected to a marker).

Mathieu

> - FChE

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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