Messages in this thread | | | Date | Fri, 8 Feb 2008 22:45:22 +0100 | From | Ingo Molnar <> | Subject | [git pull] latency tracer |
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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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