Re: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs

[Lin Ming]

On Tue, 2010-05-11 at 15:21 +0800, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > What we do not want are exhaustive event lists for specific PMU 
> > implementations, those are best left for userspace.
> 
> I'd refine this the following way:
> 
>  - We mandate proper in-kernel enumeration of all things event sources, for
>    example /sys/devices/system/node/nodeN/node_events. Obviously an event source
>    needs to be addressable for it to be useful to userspace.
> 
>  - We want generalized events expressed in those event containers that
>    are used commonly. Whatever people find useful we can enumerate and what
>    is enumerated is an ABI.
> 
>  - The 'rest' can go into /sys/devices/system/node/nodeN/node_events/raw_event/.
>    These will never be guaranteed in an ABI way really (although will work in
>    some cases) - those using raw event codes are really up to themselves and 
>    if it ever gets in the way of proper, more expressive 
>    enumeration/generalization it will have to yield.
> 
> These are the ground rules as i see them.
> 
> 	Ingo

How will this sysfs interface be used for userspace tool?

 /sys/devices/system/node/nodeN/node_events
                               node_events/event_source_id

                               node_events/local_misses/event_id
                                          /local_hits/event_id
                                          /remote_misses/event_id
                                          /remote_hits/event_id

For example, to monitor node event local_misses on node 0, does it work
as below?

1. perf top -e local_misses -n 0 (-n 0 means node 0)

2. read /sys/devices/system/node/node0/node_events/event_source_id to
get the pmu_id

3. read /sys/devices/system/node/node0/node_events/local_misses/event_id
to get the event_id

4. event_attr::pmu_id=pmu_id, event::config=event_id

5. other setting...

6. call syscall perf_event_open(....)

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