• Peter Zijlstra's avatar
    perf_counter: PERF_SAMPLE_ID and inherited counters · 7f453c24
    Peter Zijlstra authored
    Anton noted that for inherited counters the counter-id as provided by
    PERF_SAMPLE_ID isn't mappable to the id found through PERF_RECORD_ID
    because each inherited counter gets its own id.
    
    His suggestion was to always return the parent counter id, since that
    is the primary counter id as exposed. However, these inherited
    counters have a unique identifier so that events like
    PERF_EVENT_PERIOD and PERF_EVENT_THROTTLE can be specific about which
    counter gets modified, which is important when trying to normalize the
    sample streams.
    
    This patch removes PERF_EVENT_PERIOD in favour of PERF_SAMPLE_PERIOD,
    which is more useful anyway, since changing periods became a lot more
    common than initially thought -- rendering PERF_EVENT_PERIOD the less
    useful solution (also, PERF_SAMPLE_PERIOD reports the more accurate
    value, since it reports the value used to trigger the overflow,
    whereas PERF_EVENT_PERIOD simply reports the requested period changed,
    which might only take effect on the next cycle).
    
    This still leaves us PERF_EVENT_THROTTLE to consider, but since that
    _should_ be a rare occurrence, and linking it to a primary id is the
    most useful bit to diagnose the problem, we introduce a
    PERF_SAMPLE_STREAM_ID, for those few cases where the full
    reconstruction is important.
    
    [Does change the ABI a little, but I see no other way out]
    Suggested-by: default avatarAnton Blanchard <anton@samba.org>
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    LKML-Reference: <1248095846.15751.8781.camel@twins>
    7f453c24
builtin-report.c 42.3 KB