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    SubjectRe: [RFC] perf_events: support for uncore a.k.a. nest units

    * Corey Ashford <> wrote:

    > I really think we need some sort of data structure which is passed from the
    > kernel to user space to represent the topology of the system, and give
    > useful information to be able to identify each PMU node. Whether this is
    > done with a sysfs-style tree, a table in a file, XML, etc... it doesn't
    > really matter much, but it needs to be something that can be parsed
    > relatively easily and *contains just enough information* for the user to be
    > able to correctly choose PMUs, and for the kernel to be able to relate that
    > back to actual PMU hardware.

    The right way would be to extend the current event description under
    /debug/tracing/events with hardware descriptors and (maybe) to formalise this
    into a separate /proc/events/ or into a separate filesystem.

    The advantage of this is that in the grand scheme of things we _really_ dont
    want to limit performance events to 'hardware' hierarchies, or to
    devices/sysfs, some existing /proc scheme, or any other arbitrary (and
    fundamentally limiting) object enumeration.

    We want a unified, logical enumeration of all events and objects that we care
    about from a performance monitoring and analysis point of view, shaped for the
    purpose of and parsed by perf user-space. And since the current event
    descriptors are already rather rich as they enumerate all sorts of things:

    - tracepoints
    - hw-breakpoints
    - dynamic probes

    etc., and are well used by tooling we should expand those with real hardware



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