linux-kernel - Re: [PATCH] tracing/kmemtrace: normalize the raw tracer event to the unified tracing API

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Date:	Tue, 30 Dec 2008 09:00:31 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Subject: Re: [PATCH] tracing/kmemtrace: normalize the raw tracer event to
	the unified tracing API

* Frederic Weisbecker <fweisbec@...il.com> wrote:

> Pekka, note that I would be pleased to add statistical tracing on this 
> tracer, but I would need a hashtable, or an array, or a list, or 
> whatever iterable to insert the data into the stat tracing api.

there would be a couple of natural objects to group events by:

	1) callsite [IP] of kmalloc()/kfree()/etc.

	2) slab cache

	3) slab object

for 1) callsite based histograms, i think ftrace should have a built-in 
mechanism for that. kmemtrace tracepoints already pass in a call_site 
argument that can be used to drive it.

for 2) slab cache based histograms (counts) - we need some knowledge about 
the affected slab caches, and we need some space as well. The tracepoints 
could be extended with a kmem_cache argument perhaps. A callback is needed 
at cache creation time (which could be in the form of a tracepoint) that 
gives kernel/tracing/kmemtrace.c the right place to allocate the per slab 
histogram. (so that the other tracepoints dont have to do it implicitly - 
which would be fragile as we are in the SLAB code, often with spinlocks 
taken, so we cannot allocate)

i think 3) is the hardest so lets skip it for now ;-)

	Ingo
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