linux-kernel - Re: [RFC PATCH] dynamic debug - adding ring buffer storage support

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Date:	Wed, 30 Dec 2009 20:44:17 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Jiri Olsa <jolsa@...hat.com>,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] dynamic debug - adding ring buffer storage support

On Wed, 2009-12-30 at 23:50 +0100, Frederic Weisbecker wrote:

> That said, I sometimes dream about one event per printk.
> 
> Having, say:
> 
> /debug/tracing/events/printk/
>          |
>          ---- kernel/
>          |      |
>          |      ------- time/
>          |      |        |
>          |      |        ---- clocksource.c
>          |      |                 |
>          |      |                 --- clocksource_unstable:218/
>          |      |                 |            |
>          |      |                 |            ---- format
>          |      |                 |            |
>          |      |                 |            ---- filter
>          |      |                 |            |
>          |      |                 |            ---- enable
>          |      |                 --- [...]
>          |      ------- [...]
>          |
>          ---- drivers/
>          |       |
>          |       ---- [...]
>          |
>          ---- [...]
> 
> 
> That would give a total control over every printk, trace_printk, etc...
> 
> Too bad that would bloat the memory.
> Well, that could be wrapped in a single, wildly implemented (understand:
> not using TRACE_EVENT macro) trace event, something able to walk through
> every calls of printk, trace_printk, early_printk, etc... and imitate
> a per printk event granularity.
> 
> But still it needs to be useful...


I think we can do the above without bloating memory. Yes we would not
need the TRACE_EVENT macro for this. The TRACE_EVENT macro is just for
generic tracing, but we could easily come up with something specific for
the printk's that will not bloat the kernel as much.

When I get some time, I may try to play with this idea.

-- Steve



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