Performance impact of CONFIG_FUNCTION_TRACER
From: Sascha Hauer
Date: Tue Jul 05 2022 - 06:55:35 EST
Hi,
I ran some lmbench subtests on a ARMv7 machine (NXP i.MX6q) with and
without CONFIG_FUNCTION_TRACER enabled (with CONFIG_DYNAMIC_FTRACE
enabled and no tracing active), see below. The Kconfig help text of this
option reads as:
> If it's runtime disabled (the bootup default), then the overhead of
> the instructions is very small and not measurable even in
> micro-benchmarks.
In my tests the overhead is small, but it surely exists and is
measurable at least on ARMv7 machines. Is this expected? Should the help
text be rephrased a little less optimistic?
lat_fs
======
CONFIG_FUNCTION_TRACER=y
------------------------
_ file size
/ _ repetitions
| / _ created files per second
| | / _ deleted files per second
| | | /
0k 205 38325 70264
1k 123 21949 41495
4k 119 21632 42365
10k 84 14408 29439
CONFIG_FUNCTION_TRACER=n
------------------------
0k 198 39317 76241
1k 125 22397 42420
4k 125 22038 44144
10k 84 14965 30032
./scripts/do_ctx
================
Measures context switch time (in us?)
CONFIG_FUNCTION_TRACER=y
------------------------
"size=0k ovr=4.60
2 16.57
4 15.75
8 16.99
16 16.93
24 18.79
32 20.11
64 22.20
96 21.59
CONFIG_FUNCTION_TRACER=n
------------------------
"size=0k ovr=4.88
2 15.26
4 17.29
8 18.25
16 18.40
24 22.19
32 20.85
64 23.32
96 23.11
lat_pipe
========
I think it measures the time between sending and receiving data
through a pipe.
CONFIG_FUNCTION_TRACER=y
------------------------
Pipe latency: 44.7039 microseconds
CONFIG_FUNCTION_TRACER=n
------------------------
Pipe latency: 41.9876 microseconds
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