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    SubjectRe: [PATCH 2/2] ext4: Convert instrumentation from markers to tracepoints

    * Theodore Ts'o <tytso@mit.edu> wrote:

    > Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    > ---
    > fs/ext4/ext4.h | 22 +--
    > fs/ext4/ext4_i.h | 12 -
    > fs/ext4/fsync.c | 8 +-
    > fs/ext4/ialloc.c | 17 +-
    > fs/ext4/inode.c | 79 ++---
    > fs/ext4/mballoc.c | 84 ++---
    > fs/ext4/mballoc.h | 68 +----
    > fs/ext4/super.c | 6 +-
    > include/linux/ext4_trace_types.h | 108 ++++++
    > include/trace/ext4.h | 8 +
    > include/trace/ext4_event_types.h | 690 +++++++++++++++++++++++++++++++++++++
    > include/trace/trace_event_types.h | 1 +
    > include/trace/trace_events.h | 1 +
    > 13 files changed, 886 insertions(+), 218 deletions(-)
    > create mode 100644 include/linux/ext4_trace_types.h
    > create mode 100644 include/trace/ext4.h
    > create mode 100644 include/trace/ext4_event_types.h

    Really nice stuff!

    A general, high-level observation: it is visible that the conversion
    to TRACE_EVENTS() does increase the total linecount, but it also
    removes code from the most often used source code areas
    (fs/ext4/*.c) - and using an intuitive function-call-alike
    single-line tracepoint there.

    I'd call that a positive effect.

    It would still be nice to compact the 690 lines of (out of line)
    ext4_event_types.h definitions some more - and i think we'll be able
    to do it without affecting the usage sites.

    OTOH, even those bits look fairly readable, and there's a fair
    amount of bang-for-bucks ratio - these tracepoints give us:

    - integrated tracepoints
    - zero-copy and per-cpu splice() based tracing
    - binary tracing without printf overhead
    - structured logging records exposed under /debug/tracing/events
    - trace events embedded in function tracer output and other plugins
    - user-defined, per tracepoint filter expressions

    ... so even if we were to keep the 690 lines of overhead with no
    further compacting, it still looks like a good deal to me, all
    things considered.

    Ingo


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