linux-kernel - Re: [RFC] Tracepoint proposal

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Message-ID: <20080622175928.GA5022@martell.zuzino.mipt.ru>
Date:	Sun, 22 Jun 2008 21:59:28 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	systemtap-ml <systemtap@...rces.redhat.com>,
	Hideo AOKI <haoki@...hat.com>
Subject: Re: [RFC] Tracepoint proposal

On Sun, Jun 22, 2008 at 01:11:35PM -0400, Mathieu Desnoyers wrote:
> Tracepoint proposal
> 
> - Tracepoint infrastructure
>   - In-kernel users
>   - Complete typing, verified by the compiler
>   - Dynamically linked and activated
> 
> - Marker infrastructure
>   - Exported API to userland
>   - Basic types only
> 
> - Dynamic vs static
>   - In-kernel probes are dynamically linked, dynamically activated, connected to
>     tracepoints. Type verification is done at compile-time. Those in-kernel
>     probes can be a probe extracting the information to put in a marker or a
>     specific in-kernel tracer such as ftrace.
>   - Information sinks (LTTng, SystemTAP) are dynamically connected to the
>     markers inserted in the probes and are dynamically activated.
> 
> - Near instrumentation site vs in a separate tracer module
> 
> A probe module, only if provided with the kernel tree, could connect to internal
> tracing sites. This argues for keeping the tracepoing probes near the
> instrumentation site code. However, if a tracer is general purpose and exports
> typing information to userspace through some mechanism, it should only export
> the "basic type" information and could be therefore shipped outside of the
> kernel tree.
> 
> In-kernel probes should be integrated to the kernel tree. They would be close to
> the instrumented kernel code and would translate between the in-kernel
> instrumentation and the "basic type" exports. Other in-kernel probes could
> provide a different output (statistics available through debugfs for instance).
> ftrace falls into this category.
> 
> Generic or specialized information "sinks" (LTTng, systemtap) could be connected
> to the markers put in tracepoint probes to extract the information to userspace.
> They would extract both typing information and the per-tracepoint execution
> information to userspace.
> 
> Therefore, the code would look like :
> 
> kernel/sched.c:
> 
> #include "sched-trace.h"
> 
> schedule()
> {
>   ...
>   trace_sched_switch(prev, next);
>   ...
> }

Once this is accepted you're going to add hundreds of such calls to every
core subsystem, right?

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