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    SubjectRe: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs
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    On Mon, 2010-05-10 at 19:27 +0800, Peter Zijlstra wrote:
    > On Mon, 2010-05-10 at 18:26 +0800, Lin Ming wrote:
    >
    > > > No, I'm assuming there is only 1 PMU per CPU. Corey is the expert on
    > > > crazy hardware though, but I think the sanest way is to extend the CPU
    > > > topology if there's more structure to it.
    > >
    > > But our goal is to support multiple pmus, don't we need to assume there
    > > are more than 1 PMU per CPU?
    >
    > No, because as I said, then its ambiguous what pmu you want. If you have
    > that, you need to extend your topology information.
    >
    > Anyway, I talked with Ingo on this and he'd like to see this somewhat
    > extended.
    >
    > Instead of a pmu_id field, which we pass into a new
    > perf_event_attr::pmu_id field, how about creating an event_source sysfs
    > class. Then each class can have an event_source_id and a hierarchy of
    > 'generic' events.
    >
    > We'd start using the PERF_TYPE_ space for this and express the
    > PERF_COUNT_ space in the event attributes found inside that class.
    >
    > That way we can include all the existing event enumerations into this as
    > well.
    >
    > This way we can create:
    >
    > /sys/devices/system/cpu/cpuN/cpu_hardware_events
    > cpu_hardware_events/event_source_id
    > cpu_hardware_events/cpu_cycles
    > cpu_hardware_events/instructions
    > /...
    >
    > /sys/devices/system/cpu/cpuN/cpu_raw_events
    > cpu_raw_events/event_source_id
    >
    >
    > These would match the current PERF_TYPE_* values for compatibility
    >
    > For new PMUs we can start a dynamic range of PERF_TYPE_ (say at 64k but
    > that's not ABI and can be changed at any time, we've got u32 to play
    > with).
    >
    > For uncore this would result in:
    >
    > /sys/devices/system/node/nodeN/node_raw_events
    > node_raw_events/event_source_id
    >
    > and maybe:
    >
    > /sys/devices/system/node/nodeN/node_events
    > node_events/event_source_id
    > node_events/local_misses
    > /local_hits
    > /remote_misses
    > /remote_hits
    > /...
    >
    >
    > The software events and tracepoints and kprobes stuff we could hang off
    > of /sys/kernel/ or something
    >
    > So your registration would indeed look like something:
    >
    > perf_event_register_pmu(struct pmu *pmu, int type),
    >
    > where type would normally be -1 (dynamic) but would be PERF_TYPE_ for
    > those already laid down in ABI.
    >
    > This approach will also give us a good overview
    > in /sys/class/event_source/, which will be a flat listing of all
    > existing event sources.
    >
    > Does this make sense?

    Thanks for the idea.

    Give me some time to get a clear understanding of the ideas from you and
    others.

    And then I'll work out a patch as soon as possible.

    Lin Ming



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