• Peter Zijlstra's avatar
    perf: Add per event clockid support · 34f43927
    Peter Zijlstra authored
    While thinking on the whole clock discussion it occurred to me we have
    two distinct uses of time:
    
     1) the tracking of event/ctx/cgroup enabled/running/stopped times
        which includes the self-monitoring support in struct
        perf_event_mmap_page.
    
     2) the actual timestamps visible in the data records.
    
    And we've been conflating them.
    
    The first is all about tracking time deltas, nobody should really care
    in what time base that happens, its all relative information, as long
    as its internally consistent it works.
    
    The second however is what people are worried about when having to
    merge their data with external sources. And here we have the
    discussion on MONOTONIC vs MONOTONIC_RAW etc..
    
    Where MONOTONIC is good for correlating between machines (static
    offset), MONOTNIC_RAW is required for correlating against a fixed rate
    hardware clock.
    
    This means configurability; now 1) makes that hard because it needs to
    be internally consistent across groups of unrelated events; which is
    why we had to have a global perf_clock().
    
    However, for 2) it doesn't really matter, perf itself doesn't care
    what it writes into the buffer.
    
    The below patch makes the distinction between these two cases by
    adding perf_event_clock() which is used for the second case. It
    further makes this configurable on a per-event basis, but adds a few
    sanity checks such that we cannot combine events with different clocks
    in confusing ways.
    
    And since we then have per-event configurability we might as well
    retain the 'legacy' behaviour as a default.
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: David Ahern <dsahern@gmail.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: John Stultz <john.stultz@linaro.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    34f43927
perf_event.c 50.9 KB