[git pull] latency tracer

From: Ingo Molnar
Date: Fri Feb 08 2008 - 16:45:46 EST

Next message: Chuck Ebbert: "Re: [patch 43/45] x86: replace LOCK_PREFIX in futex.h"
Previous message: Alan Cox: "Re: [PATCH] USB: mark USB drivers as being GPL only"
Next in thread: Ingo Molnar: "Re: [git pull] latency tracer"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Next message: Chuck Ebbert: "Re: [patch 43/45] x86: replace LOCK_PREFIX in futex.h"
Previous message: Alan Cox: "Re: [PATCH] USB: mark USB drivers as being GPL only"
Next in thread: Ingo Molnar: "Re: [git pull] latency tracer"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]