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| author | Steven Rostedt (VMware) | 2019-05-10 18:05:46 +0200 |
|---|---|---|
| committer | Steven Rostedt (VMware) | 2019-05-10 18:33:03 +0200 |
| commit | 518049d9d3e25dcd7be6e3d728e86f292ad0c922 (patch) | |
| tree | fdc458e59447517e471a9113d8f32f11cb4d4a8d /arch/x86/Kconfig | |
| parent | tracing: Simplify "if" macro code (diff) | |
| download | kernel-qcow2-linux-518049d9d3e25dcd7be6e3d728e86f292ad0c922.tar.gz kernel-qcow2-linux-518049d9d3e25dcd7be6e3d728e86f292ad0c922.tar.xz kernel-qcow2-linux-518049d9d3e25dcd7be6e3d728e86f292ad0c922.zip | |
ftrace/x86_32: Remove support for non DYNAMIC_FTRACE
When DYNAMIC_FTRACE is enabled in the kernel, all the functions that can be
traced by the function tracer have a "nop" placeholder at the start of the
function. When function tracing is enabled, the nop is converted into a call
to the tracing infrastructure where the functions get traced. This also
allows for specifying specific functions to trace, and a lot of
infrastructure is built on top of this.
When DYNAMIC_FTRACE is not enabled, all the functions have a call to the
ftrace trampoline. A check is made to see if a function pointer is the
ftrace_stub or not, and if it is not, it calls the function pointer to trace
the code. This adds over 10% overhead to the kernel even when tracing is
disabled.
When an architecture supports DYNAMIC_FTRACE there really is no reason to
use the static tracing. I have kept non DYNAMIC_FTRACE available in x86 so
that the generic code for non DYNAMIC_FTRACE can be tested. There is no
reason to support non DYNAMIC_FTRACE for both x86_64 and x86_32. As the non
DYNAMIC_FTRACE for x86_32 does not even support fentry, and we want to
remove mcount completely, there's no reason to keep non DYNAMIC_FTRACE
around for x86_32.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'arch/x86/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 5ad92419be19..0544041ae3a2 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -31,6 +31,17 @@ config X86_64 select X86_DEV_DMA_OPS select ARCH_HAS_SYSCALL_WRAPPER +config FORCE_DYNAMIC_FTRACE + def_bool y + depends on X86_32 + depends on FUNCTION_TRACER + select DYNAMIC_FTRACE + help + We keep the static function tracing (!DYNAMIC_FTRACE) around + in order to test the non static function tracing in the + generic code, as other architectures still use it. But we + only need to keep it around for x86_64. No need to keep it + for x86_32. For x86_32, force DYNAMIC_FTRACE. # # Arch settings # |