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    Subject[git pull] latency tracer

    Linus, please pull the latency tracer tree from:

    git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched.git

    Find the shortlog below.

    This is the latency tracer from -rt, split up and much cleaned up by
    Steve Rostedt, Arnaldo Carvalho and myself. The main motivation of this
    tracer is to be utilized by high-level user tools such as LatencyTOP, to
    analyze system behavior and to enable users to give feedback to kernel
    developers.

    It has been in -rt for years and was found to be very useful there, and
    in the last month it has been posted to lkml by Steve about 10 times.
    [This final version is simpler and cleaner than the last lkml version
    (v10) - lets start simple. ]

    It does include one very interesting new feature that deserves to be
    mentioned outside of the shortlog: 'dynamic ftrace' - which is a
    transparent kernel-image-patcher mechanism that lazily patches out
    mcount callsites from all functions that get executed. [if tracing is
    disabled] These patched out callsites are remembered, and are patched
    back in when tracing is enabled.

    This technique does not just accelelerate the "tracing disabled" case
    enormously, we were in fact unable to measure _any_ performance
    difference (within noise) between an mcount-enabled dyn-ftrace [but
    tracing-disabled] and a vanilla kernel (!), on modern CPUs.

    There is still the cost of the +5 byte function size that mcount causes,
    and the resulting +~1% kernel text size increase, but the overhead was
    not measurable in micro or macro benchmarks that we tried. (probably
    because there are no branches added to the hot paths and the only
    overhead is the NOP that is inserted into the prologue of the function -
    which modern CPUs will just eat up as if it didnt exist.)

    All in one, i think this is one of the most promising developments in
    terms of Linux kernel instrumentation that happened in the past few
    years:

    - it gives us full, very meaningful instrumentation (there are
    70,000+ function calls in an allyesconfig kernel)

    - the instrumentation sites can be flexibly selected and there's no
    measurable performance overhead (that we could measure)

    - there's near zero "collateral" maintenance overhead to other
    subsystems (!)

    - the technique [of mcount based tracing] has been tested in -rt for
    years so we know the impact pretty well.

    - the mcount call sites [on exported functions] can be used by
    SystemTap to do low-overhead patching as well and to access the
    function parameters in a predictable way. [as long as the parameter
    signature of the function does not change.]

    And no, i'm not biased at all ;-)

    there are 6 tracers available with this pull:

    # cat /debug/tracing/available_tracers
    wakeup preemptirqsoff preemptoff irqsoff ftrace sched_switch none

    these are the well-known and popular tracer variants from -rt. (But i'd
    expect more tracers to show up - the design is extensible.)

    the patch does change generic include files too, so i made a test-build
    on ppc64 as well (besides the usual x86 grind), and it built fine. No
    architectures are supposed to (or expected to) break.

    ( This tree also includes the RCU enhancements for NO_HZ - Steve's box
    was locking up under PREEMPT_RCU without this. These bits have been
    under testing for months too. )

    Thanks,

    Ingo

    ------------------>
    Arnaldo Carvalho de Melo (2):
    ftrace: add basic support for gcc profiler instrumentation
    ftrace: annotate core code that should not be traced

    Ingo Molnar (3):
    sched: add latency tracer callbacks to the scheduler
    ftrace: output formatting
    ftrace: dyn overflow debug

    Steven Rostedt (19):
    rcu: add support for dynamic ticks and preempt rcu
    printk: dont wake up klogd with the rq locked
    ftrace: add preempt_enable/disable notrace macros
    x86: add notrace annotations to vsyscall.
    ftrace: latency tracer infrastructure
    ftrace: function tracer
    ftrace: make the task state char-string visible to all
    ftrace: add tracing of context switches
    ftrace: tracer for scheduler wakeup latency
    ftrace: trace irq disabled critical timings
    ftrace: trace preempt off critical timings
    ftrace: have ftrace use its ret as the dummy function
    ftrace: remove ftrace_enabled variable
    ftrace: add notrace annotations for NMI routines
    ftrace: dynamic enabling/disabling of function calls
    ftrace: add ftrace_enabled sysctl to disable mcount function
    ftrace: calculate instruction instead of storing it
    ftrace: use an atomic counter for sorting
    ftrace: make "none" the default tracer

    Makefile | 3 +
    arch/x86/Kconfig | 1 +
    arch/x86/kernel/Makefile | 1 +
    arch/x86/kernel/entry_32.S | 27 +
    arch/x86/kernel/entry_64.S | 37 +
    arch/x86/kernel/ftrace.c | 237 ++++++
    arch/x86/kernel/nmi_32.c | 3 +-
    arch/x86/kernel/nmi_64.c | 6 +-
    arch/x86/kernel/process_32.c | 3 +
    arch/x86/kernel/process_64.c | 3 +
    arch/x86/kernel/traps_32.c | 12 +-
    arch/x86/kernel/traps_64.c | 11 +-
    arch/x86/kernel/vsyscall_64.c | 3 +-
    arch/x86/lib/Makefile | 1 +
    arch/x86/lib/thunk_32.S | 47 ++
    arch/x86/lib/thunk_64.S | 19 +-
    arch/x86/vdso/vclock_gettime.c | 15 +-
    arch/x86/vdso/vgetcpu.c | 3 +-
    include/asm-x86/irqflags.h | 24 +-
    include/asm-x86/vsyscall.h | 3 +-
    include/linux/ftrace.h | 92 +++
    include/linux/hardirq.h | 10 +
    include/linux/irqflags.h | 13 +-
    include/linux/linkage.h | 8 +
    include/linux/preempt.h | 34 +-
    include/linux/rcuclassic.h | 3 +
    include/linux/rcupreempt.h | 22 +
    include/linux/sched.h | 30 +
    kernel/Makefile | 2 +
    kernel/fork.c | 2 +-
    kernel/lockdep.c | 23 +-
    kernel/printk.c | 16 +-
    kernel/rcupreempt.c | 224 ++++++-
    kernel/sched.c | 47 ++-
    kernel/softirq.c | 1 +
    kernel/sysctl.c | 11 +
    kernel/time/tick-sched.c | 3 +
    kernel/trace/Kconfig | 111 +++
    kernel/trace/Makefile | 10 +
    kernel/trace/ftrace.c | 521 +++++++++++++
    kernel/trace/trace.c | 1547 +++++++++++++++++++++++++++++++++++++
    kernel/trace/trace.h | 185 +++++
    kernel/trace/trace_functions.c | 73 ++
    kernel/trace/trace_irqsoff.c | 505 ++++++++++++
    kernel/trace/trace_sched_switch.c | 125 +++
    kernel/trace/trace_sched_wakeup.c | 310 ++++++++
    lib/Kconfig.debug | 2 +
    lib/smp_processor_id.c | 2 +-
    48 files changed, 4324 insertions(+), 67 deletions(-)
    create mode 100644 arch/x86/kernel/ftrace.c
    create mode 100644 arch/x86/lib/thunk_32.S
    create mode 100644 include/linux/ftrace.h
    create mode 100644 kernel/trace/Kconfig
    create mode 100644 kernel/trace/Makefile
    create mode 100644 kernel/trace/ftrace.c
    create mode 100644 kernel/trace/trace.c
    create mode 100644 kernel/trace/trace.h
    create mode 100644 kernel/trace/trace_functions.c
    create mode 100644 kernel/trace/trace_irqsoff.c
    create mode 100644 kernel/trace/trace_sched_switch.c
    create mode 100644 kernel/trace/trace_sched_wakeup.c



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