A couple of months ago I was playing with getting recursion
fixed with the function tracer. There's a lot of places that could
use improvements, and I also found a few cases where the recursion
protection would have false positives causing missed function tracing.
I implemented a per context bit checking (Normal, SoftIRQ, IRQ and NMI).
Using 4 bits in the task_struct trace_recursion field, I was
able to fix these issues as well as improve the speed of the function
tracer and ring buffer.
Before the patches I had:
# echo function > /debug/tracing/current_tracer
# for i in `seq 10`; do ./hackbench 50; done
Time: 12.028
Time: 11.945
Time: 11.925
Time: 11.964
Time: 12.002
Time: 11.910
Time: 11.944
Time: 11.929
Time: 11.941
Time: 11.924
(average: 11.9512)
Now we have:
# echo function > /debug/tracing/current_tracer
# for i in `seq 10`; do ./hackbench 50; done
Time: 9.712
Time: 9.824
Time: 9.861
Time: 9.827
Time: 9.962
Time: 9.905
Time: 9.886
Time: 10.088
Time: 9.861
Time: 9.834
(average: 9.876)
This is a total of a 17.4% improvement in function tracing!
Steven Rostedt (8):
ftrace: Fix global function tracers that are not recursion safe
ftrace: Fix function tracing recursion self test
ftrace: Optimize the function tracer list loop
ftrace: Add context level recursion bit checking
tracing: Make the trace recursion bits into enums
tracing: Avoid unnecessary multiple recursion checks
ftrace: Use only the preempt version of function tracing
ring-buffer: User context bit recursion checking
----
kernel/trace/ftrace.c | 82 ++++++++++++++++---------
kernel/trace/ring_buffer.c | 85 +++++++++++++++++--------
kernel/trace/trace.h | 133 ++++++++++++++++++++++++++++++++++++----
kernel/trace/trace_functions.c | 61 +++++-------------
kernel/trace/trace_selftest.c | 3 +-
5 files changed, 248 insertions(+), 116 deletions(-)
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