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    Subject[PATCHSET 0/5] perf ftrace: Implement function latency histogram (v2)
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    Hello,

    I've implemented 'latency' subcommand in the perf ftrace command to
    show a histogram of function latency.

    v2 changes)
    * fix build errors (Arnaldo)
    * add Arnaldo's test results in the commit message
    * show warning when -b is used and BPF support is not enabled (Athira)
    * use skel->links to save bpf links (Song)

    To handle new subcommands, the existing functionality is moved to
    'trace' subcommand while preserving backward compatibility of not
    having a subcommand at all (defaults to 'trace').

    The latency subcommand accepts a target (kernel, for now) function
    with -T option and shows a histogram like below:

    $ sudo ./perf ftrace latency -a -T mutex_lock sleep 1
    # DURATION | COUNT | GRAPH |
    0 - 1 us | 2686 | ###################### |
    1 - 2 us | 976 | ######## |
    2 - 4 us | 879 | ####### |
    4 - 8 us | 481 | #### |
    8 - 16 us | 445 | ### |
    16 - 32 us | 1 | |
    32 - 64 us | 0 | |
    64 - 128 us | 0 | |
    128 - 256 us | 0 | |
    256 - 512 us | 0 | |
    512 - 1024 us | 0 | |
    1 - 2 ms | 0 | |
    2 - 4 ms | 0 | |
    4 - 8 ms | 0 | |
    8 - 16 ms | 0 | |
    16 - 32 ms | 0 | |
    32 - 64 ms | 0 | |
    64 - 128 ms | 0 | |
    128 - 256 ms | 0 | |
    256 - 512 ms | 0 | |
    512 - 1024 ms | 0 | |
    1 - ... s | 0 | |

    It basically use the function graph tracer to extract the duration of
    the function. But with -b/--use-bpf option, it can use BPF to save
    the histogram in the kernel. For the same function, it gets:

    $ sudo ./perf ftrace latency -a -b -T mutex_lock sleep 1
    # DURATION | COUNT | GRAPH |
    0 - 1 us | 4682 | ############################################# |
    1 - 2 us | 11 | |
    2 - 4 us | 0 | |
    4 - 8 us | 0 | |
    8 - 16 us | 7 | |
    16 - 32 us | 6 | |
    32 - 64 us | 0 | |
    64 - 128 us | 0 | |
    128 - 256 us | 0 | |
    256 - 512 us | 0 | |
    512 - 1024 us | 0 | |
    1 - 2 ms | 0 | |
    2 - 4 ms | 0 | |
    4 - 8 ms | 0 | |
    8 - 16 ms | 0 | |
    16 - 32 ms | 0 | |
    32 - 64 ms | 0 | |
    64 - 128 ms | 0 | |
    128 - 256 ms | 0 | |
    256 - 512 ms | 0 | |
    512 - 1024 ms | 0 | |
    1 - ... s | 0 | |


    You can get the patches at 'perf/ftrace-latency-v2' branch on

    https://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git


    Thanks,
    Namhyung


    Namhyung Kim (5):
    perf ftrace: Add 'trace' subcommand
    perf ftrace: Move out common code from __cmd_ftrace
    perf ftrace: Add 'latency' subcommand
    perf ftrace: Add -b/--use-bpf option for latency subcommand
    perf ftrace: Implement cpu and task filters in BPF

    tools/perf/Makefile.perf | 2 +-
    tools/perf/builtin-ftrace.c | 445 +++++++++++++++++---
    tools/perf/util/Build | 1 +
    tools/perf/util/bpf_ftrace.c | 152 +++++++
    tools/perf/util/bpf_skel/func_latency.bpf.c | 114 +++++
    tools/perf/util/ftrace.h | 81 ++++
    6 files changed, 725 insertions(+), 70 deletions(-)
    create mode 100644 tools/perf/util/bpf_ftrace.c
    create mode 100644 tools/perf/util/bpf_skel/func_latency.bpf.c
    create mode 100644 tools/perf/util/ftrace.h


    base-commit: 8ff4f20f3eb55dea0dbbe5e32043ab6b7427882f
    --
    2.34.1.173.g76aa8bc2d0-goog

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