From 518049d9d3e25dcd7be6e3d728e86f292ad0c922 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Fri, 10 May 2019 12:05:46 -0400 Subject: 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) --- arch/x86/Kconfig | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'arch/x86/Kconfig') 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 # -- cgit v1.2.3