• Ian Munsie's avatar
    perf session: Fallback to unordered processing if no sample_id_all · 21ef97f0
    Ian Munsie authored
    If we are running the new perf on an old kernel without support for
    sample_id_all, we should fall back to the old unordered processing of
    events. If we didn't than we would *always* process events without
    timestamps out of order, whether or not we hit a reordering race. In
    other words, instead of there being a chance of not attributing samples
    correctly, we would guarantee that samples would not be attributed.
    
    While processing all events without timestamps before events with
    timestamps may seem like an intuitive solution, it falls down as
    PERF_RECORD_EXIT events would also be processed before any samples.
    Even with a workaround for that case, samples before/after an exec would
    not be attributed correctly.
    
    This patch allows commands to indicate whether they need to fall back to
    unordered processing, so that commands that do not care about timestamps
    on every event will not be affected. If we do fallback, this will print
    out a warning if report -D was invoked.
    
    This patch adds the test in perf_session__new so that we only need to
    test once per session. Commands that do not use an event_ops (such as
    record and top) can simply pass NULL in it's place.
    Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    LKML-Reference: <1291951882-sup-6069@au1.ibm.com>
    Signed-off-by: default avatarIan Munsie <imunsie@au1.ibm.com>
    Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    21ef97f0
builtin-diff.c 6.06 KB