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ftrace: Add sample with custom ops

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When reworking core ftrace code or architectural ftrace code, it's often
necessary to test/analyse/benchmark a number of ftrace_ops
configurations. This patch adds a module which can be used to explore
some of those configurations.

I'm using this to benchmark various options for changing the way
trampolines and handling of ftrace_ops work on arm64, and ensuring other
architectures aren't adversely affected.

For example, in a QEMU+KVM VM running on a 2GHz Xeon E5-2660
workstation, loading the module in various configurations produces:

| # insmod ftrace-ops.ko
| ftrace_ops: registering:
|   relevant ops: 1
|     tracee: tracee_relevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   irrelevant ops: 0
|     tracee: tracee_irrelevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   saving registers: NO
|   assist recursion: NO
|   assist RCU: NO
| ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 1681558ns (16ns / call)

| # insmod ftrace-ops.ko nr_ops_irrelevant=5
| ftrace_ops: registering:
|   relevant ops: 1
|     tracee: tracee_relevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   irrelevant ops: 5
|     tracee: tracee_irrelevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   saving registers: NO
|   assist recursion: NO
|   assist RCU: NO
| ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 1693042ns (16ns / call)

| # insmod ftrace-ops.ko nr_ops_relevant=2
| ftrace_ops: registering:
|   relevant ops: 2
|     tracee: tracee_relevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   irrelevant ops: 0
|     tracee: tracee_irrelevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   saving registers: NO
|   assist recursion: NO
|   assist RCU: NO
| ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 11965582ns (119ns / call)

| # insmod ftrace-ops.ko save_regs=true
| ftrace_ops: registering:
|   relevant ops: 1
|     tracee: tracee_relevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   irrelevant ops: 0
|     tracee: tracee_irrelevant [ftrace_ops]
|     tracer: ops_func_nop [ftrace_ops]
|   saving registers: YES
|   assist recursion: NO
|   assist RCU: NO
| ftrace_ops: Attempted 100000 calls to tracee_relevant [ftrace_ops] in 4459624ns (44ns / call)

Link: https://lkml.kernel.org/r/20230103124912.2948963-4-mark.rutland@arm.com

Cc: Florent Revest <revest@chromium.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Mark Rutland
2023-01-03 12:49:12 +00:00
committed by Steven Rostedt (Google)
parent 7f09d639b8
commit b56c68f705
4 changed files with 261 additions and 0 deletions
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7
samples/Kconfig
View File

@@ -46,6 +46,13 @@ config SAMPLE_FTRACE_DIRECT_MULTI
that hooks to wake_up_process and schedule, and prints
the function addresses.
config SAMPLE_FTRACE_OPS
tristate "Build custom ftrace ops example"
depends on FUNCTION_TRACER
help
This builds an ftrace ops example that hooks two functions and
measures the time taken to invoke one function a number of times.
config SAMPLE_TRACE_ARRAY
tristate "Build sample module for kernel access to Ftrace instancess"
depends on EVENT_TRACING && m