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SubjectRe: [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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