[PATCH v3 0/3] *** Latency histograms - IRQSOFF,PREEMPTOFF ***

[Binoy Jayan]

Hi,

Thank you Steven and Daniel for reviewing v1 and providing suggestions.
These set of patches [v3] capture latency events caused by interrupts and
premption disabled in kernel. The patches are based on the hist trigger
feature developed by Tom Zanussi.

v2: https://lkml.org/lkml/2016/8/24/296

Mount Debugfs

mount -t debugfs nodev /sys/kernel/debug

Examples of triggers:
echo 'hist:key=latency.log2:val=hitcount:sort=latency' > /sys/kernel/debug/tracing/events/latency/latency_preempt/trigger
echo 'hist:key=cpu,latency:val=hitcount:sort=latency if cpu==1' > /sys/kernel/debug/tracing/events/latency/latency_preempt/trigger
echo 'hist:key=ltype,cpu:val=latency:sort=ltype,cpu if ltype==0' > /sys/kernel/debug/tracing/events/latency/latency_preempt/trigger

Histogram output:
cat /sys/kernel/debug/tracing/events/latency/latency_preempt/hist

Changes from v2 as per comments from Daniel
  - Use single tracepoint for irq/preempt/critical timings by introducing
    a trace type field to differentiate trace type in the same tracepoint.
    The suspicious RCU usage error was fixed and made part of Daniel's bugfix.

TODO:
1. perf interface. Not sure if this is needed
2. Latency histograms - process wakeup latency

Binoy

Binoy Jayan (2):
  tracing: Add trace_irqsoff tracepoints
  tracing: Histogram for missed timer offsets

Daniel Wagner (1):
  tracing: Deference pointers without RCU checks

 include/linux/hrtimer.h             |  3 ++
 include/linux/rculist.h             | 36 ++++++++++++++++++++
 include/linux/tracepoint.h          |  4 +--
 include/trace/events/latency.h      | 68 +++++++++++++++++++++++++++++++++++++
 kernel/time/hrtimer.c               | 39 +++++++++++++++++++++
 kernel/trace/trace_events_filter.c  |  4 +--
 kernel/trace/trace_events_trigger.c |  6 ++--
 kernel/trace/trace_irqsoff.c        | 45 +++++++++++++++++++++++-
 8 files changed, 197 insertions(+), 8 deletions(-)
 create mode 100644 include/trace/events/latency.h

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