Eric Lee / smarc-fsl-linux-kernel

02 Apr, 2015

1 commit

  • 5c7fc2d27   samples/bpf: Add IO latency analysis (iosnoop/heatmap) tool ... Browse Code ยป

    BPF C program attaches to
    blk_mq_start_request()/blk_update_request() kprobe events to
    calculate IO latency.

    For every completed block IO event it computes the time delta
    in nsec and records in a histogram map:

    map[log10(delta)*10]++

    User space reads this histogram map every 2 seconds and prints
    it as a 'heatmap' using gray shades of text terminal. Black
    spaces have many events and white spaces have very few events.
    Left most space is the smallest latency, right most space is
    the largest latency in the range.

    Usage:

    $ sudo ./tracex3
    and do 'sudo dd if=/dev/sda of=/dev/null' in other terminal.

    Observe IO latencies and how different activity (like 'make
    kernel') affects it.

    Similar experiments can be done for network transmit latencies,
    syscalls, etc.

    '-t' flag prints the heatmap using normal ascii characters:

    $ sudo ./tracex3 -t
    heatmap of IO latency
    # - many events with this latency
    - few events
    |1us |10us |100us |1ms |10ms |100ms |1s |10s
    *ooo. *O.#. # 221
    . *# . # 125
    .. .o#*.. # 55
    . . . . .#O # 37
    .# # 175
    .#*. # 37
    # # 199
    . . *#*. # 55
    *#..* # 42
    # # 266
    ...***Oo#*OO**o#* . # 629
    # # 271
    . .#o* o.*o* # 221
    . . o* *#O.. # 50

    Signed-off-by: Alexei Starovoitov
    Cc: Arnaldo Carvalho de Melo
    Cc: Arnaldo Carvalho de Melo
    Cc: Daniel Borkmann
    Cc: David S. Miller
    Cc: Jiri Olsa
    Cc: Linus Torvalds
    Cc: Masami Hiramatsu
    Cc: Namhyung Kim
    Cc: Peter Zijlstra
    Cc: Peter Zijlstra
    Cc: Steven Rostedt
    Link: http://lkml.kernel.org/r/1427312966-8434-9-git-send-email-ast@plumgrid.com
    Signed-off-by: Ingo Molnar

    Alexei Starovoitov