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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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