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    Subject[PATCH v4 0/5] perf/sdt: SDT events listing/probing
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    This patchset helps in listing dtrace style markers(SDT) present in user space
    applications through perf.
    Notes/markers are placed at important places by the
    developers. They have a negligible overhead when not enabled.
    We can enable them and probe at these places and find some important information
    like the arguments' values, etc.

    We have lots of applications which use SDT markers today, like:
    Postgresql, MySql, Mozilla, Perl, Python, Java, Ruby, libvirt, QEMU, glib

    To add SDT markers into user applications:
    We need to have this header sys/sdt.h present.
    sys/sdt.h used is version 3.
    If not present, install systemtap-sdt-devel package (for fedora-20).

    With this patchset,
    - Use perf sdt-cache --add to add SDT events to a cache.
    # perf sdt-cache --add ./user_app
    4 SDT events added for /home/user/user_app!

    - Use perf sdt-cache --del to remove SDT events from the cache>
    # perf sdt-cache --del ./user_app
    4 events removed for /home/user/user_app!

    - Dump the cache onto stdout using perf sdt-cache --dump:
    # perf sdt-cache --dump
    /home/user/user_app :
    %user_app:foo_start
    %user_app:fun_start

    - To probe and trace an SDT event :
    # perf record -e %user_app:foo_start -aR sleep 10

    The support for perf to sdt events has undergone a lot of changes since it was
    introduced. After a lot of discussions (https://lkml.org/lkml/2014/7/20/284), the
    patchset is subdivided for ease of review.
    Previously, a patchset supporting "perf list sdt" was posted, but it didn't make
    much sense since, only listing SDT events for an ELF won't help.
    This patchset aims at adding a sub-command "sdt-cache" to perf to manage a cache
    for management of the SDT events.

    This link shows an example of marker probing with Systemtap:
    https://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps

    This link provides important info regarding SDT notes:
    http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation

    - Markers in binaries :
    These SDT markers are present in the ELF in the section named
    ".note.stapsdt".
    Here, the name of the marker, its provider, type, location, base
    address, semaphore address.
    We can retrieve these values using the members name_off and desc_off in
    Nhdr structure. If these are not enabled, they are present in the ELF as nop.

    Changes since last series:
    - Changed to use the new --quiet option added by Masami to silently
    add/delete SDT events for "perf record".
    - Now, the options are used with 'PARSE_OPT_EXCLUSIVE' added by Namhyung Kim.
    - Addressed the other review comments made by Masami and Namhyung.
    - Fixed some bugs.

    TODO:
    - Add support to add most of the SDT events on a system to the cache.
    - Recognizing arguments and support to probe on them.

    ---

    Hemant Kumar (5):
    perf/sdt: ELF support for SDT
    perf/sdt: Add SDT events into a cache
    perf/sdt: Show SDT cache contents
    perf/sdt: Delete SDT events from cache
    perf/sdt: Add support to perf record to trace SDT events


    tools/perf/Documentation/perf-sdt-cache.txt | 36 +
    tools/perf/Makefile.perf | 4
    tools/perf/builtin-probe.c | 5
    tools/perf/builtin-record.c | 23 +
    tools/perf/builtin-sdt-cache.c | 104 +++
    tools/perf/builtin.h | 1
    tools/perf/command-list.txt | 1
    tools/perf/perf.c | 1
    tools/perf/util/parse-events.c | 6
    tools/perf/util/parse-events.h | 7
    tools/perf/util/probe-event.c | 85 ++-
    tools/perf/util/probe-event.h | 8
    tools/perf/util/probe-finder.c | 3
    tools/perf/util/sdt.c | 899 +++++++++++++++++++++++++++
    tools/perf/util/symbol-elf.c | 252 ++++++++
    tools/perf/util/symbol.h | 23 +
    16 files changed, 1448 insertions(+), 10 deletions(-)
    create mode 100644 tools/perf/Documentation/perf-sdt-cache.txt
    create mode 100644 tools/perf/builtin-sdt-cache.c
    create mode 100644 tools/perf/util/sdt.c

    --



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