# SPDX-License-Identifier: GPL-2.0-only## Architectures that offer an FUNCTION_TRACER implementation should# select HAVE_FUNCTION_TRACER:# config USER_STACKTRACE_SUPPORT bool config NOP_TRACER bool config HAVE_FUNCTION_TRACER bool help See Documentation/trace/ftrace-design.rst config HAVE_FUNCTION_GRAPH_TRACER bool help See Documentation/trace/ftrace-design.rst config HAVE_DYNAMIC_FTRACE bool help See Documentation/trace/ftrace-design.rst config HAVE_DYNAMIC_FTRACE_WITH_REGS bool config HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS bool config HAVE_DYNAMIC_FTRACE_WITH_ARGS bool help If this is set, then arguments and stack can be found from the pt_regs passed into the function callback regs parameter by default, even without setting the REGS flag in the ftrace_ops. This allows for use of regs_get_kernel_argument() and kernel_stack_pointer(). config HAVE_FTRACE_MCOUNT_RECORD bool help See Documentation/trace/ftrace-design.rst config HAVE_SYSCALL_TRACEPOINTS bool help See Documentation/trace/ftrace-design.rst config HAVE_FENTRY bool help Arch supports the gcc options -pg with -mfentry config HAVE_NOP_MCOUNT bool help Arch supports the gcc options -pg with -mrecord-mcount and -nop-mcount config HAVE_C_RECORDMCOUNT bool help C version of recordmcount available? config TRACER_MAX_TRACE bool config TRACE_CLOCK bool config RING_BUFFER bool select TRACE_CLOCK select IRQ_WORK config EVENT_TRACING select CONTEXT_SWITCH_TRACER select GLOB bool config CONTEXT_SWITCH_TRACER bool config RING_BUFFER_ALLOW_SWAP bool help Allow the use of ring_buffer_swap_cpu. Adds a very slight overhead to tracing when enabled. config PREEMPTIRQ_TRACEPOINTS bool depends on TRACE_PREEMPT_TOGGLE || TRACE_IRQFLAGS select TRACING default y help Create preempt/irq toggle tracepoints if needed, so that other parts of the kernel can use them to generate or add hooks to them. # All tracer options should select GENERIC_TRACER. For those options that are# enabled by all tracers (context switch and event tracer) they select TRACING.# This allows those options to appear when no other tracer is selected. But the# options do not appear when something else selects it. We need the two options# GENERIC_TRACER and TRACING to avoid circular dependencies to accomplish the# hiding of the automatic options. config TRACING bool select RING_BUFFER select STACKTRACE if STACKTRACE_SUPPORT select TRACEPOINTS select NOP_TRACER select BINARY_PRINTF select EVENT_TRACING select TRACE_CLOCK config GENERIC_TRACER bool select TRACING ## Minimum requirements an architecture has to meet for us to# be able to offer generic tracing facilities:#config TRACING_SUPPORT bool depends on TRACE_IRQFLAGS_SUPPORT depends on STACKTRACE_SUPPORT default y if TRACING_SUPPORT menuconfig FTRACE bool "Tracers" default y if DEBUG_KERNEL help Enable the kernel tracing infrastructure. if FTRACE config BOOTTIME_TRACING bool "Boot-time Tracing support" depends on TRACING select BOOT_CONFIG help Enable developer to setup ftrace subsystem via supplemental kernel cmdline at boot time for debugging (tracing) driver initialization and boot process. config FUNCTION_TRACER bool "Kernel Function Tracer" depends on HAVE_FUNCTION_TRACER select KALLSYMS select GENERIC_TRACER select CONTEXT_SWITCH_TRACER select GLOB select TASKS_RCU if PREEMPTION select TASKS_RUDE_RCU help Enable the kernel to trace every kernel function. This is done by using a compiler feature to insert a small, 5-byte No-Operation instruction at the beginning of every kernel function, which NOP sequence is then dynamically patched into a tracer call when tracing is enabled by the administrator. If it's runtime disabled (the bootup default), then the overhead of the instructions is very small and not measurable even in micro-benchmarks. config FUNCTION_GRAPH_TRACER bool "Kernel Function Graph Tracer" depends on HAVE_FUNCTION_GRAPH_TRACER depends on FUNCTION_TRACER depends on !X86_32 || !CC_OPTIMIZE_FOR_SIZE default y help Enable the kernel to trace a function at both its return and its entry. Its first purpose is to trace the duration of functions and draw a call graph for each thread with some information like the return value. This is done by setting the current return address on the current task structure into a stack of calls. config DYNAMIC_FTRACE bool "enable/disable function tracing dynamically" depends on FUNCTION_TRACER depends on HAVE_DYNAMIC_FTRACE default y help This option will modify all the calls to function tracing dynamically (will patch them out of the binary image and replace them with a No-Op instruction) on boot up. During compile time, a table is made of all the locations that ftrace can function trace, and this table is linked into the kernel image. When this is enabled, functions can be individually enabled, and the functions not enabled will not affect performance of the system. See the files in /sys/kernel/debug/tracing: available_filter_functions set_ftrace_filter set_ftrace_notrace This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but otherwise has native performance as long as no tracing is active. config DYNAMIC_FTRACE_WITH_REGS def_bool y depends on DYNAMIC_FTRACE depends on HAVE_DYNAMIC_FTRACE_WITH_REGS config DYNAMIC_FTRACE_WITH_DIRECT_CALLS def_bool y depends on DYNAMIC_FTRACE_WITH_REGS depends on HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS config FUNCTION_PROFILER bool "Kernel function profiler" depends on FUNCTION_TRACER default n help This option enables the kernel function profiler. A file is created in debugfs called function_profile_enabled which defaults to zero. When a 1 is echoed into this file profiling begins, and when a zero is entered, profiling stops. A "functions" file is created in the trace_stat directory; this file shows the list of functions that have been hit and their counters. If in doubt, say N. config STACK_TRACER bool "Trace max stack" depends on HAVE_FUNCTION_TRACER select FUNCTION_TRACER select STACKTRACE select KALLSYMS help This special tracer records the maximum stack footprint of the kernel and displays it in /sys/kernel/debug/tracing/stack_trace. This tracer works by hooking into every function call that the kernel executes, and keeping a maximum stack depth value and stack-trace saved. If this is configured with DYNAMIC_FTRACE then it will not have any overhead while the stack tracer is disabled. To enable the stack tracer on bootup, pass in 'stacktrace' on the kernel command line. The stack tracer can also be enabled or disabled via the sysctl kernel.stack_tracer_enabled Say N if unsure. config TRACE_PREEMPT_TOGGLE bool help Enables hooks which will be called when preemption is first disabled, and last enabled. config IRQSOFF_TRACER bool "Interrupts-off Latency Tracer" default n depends on TRACE_IRQFLAGS_SUPPORT select TRACE_IRQFLAGS select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP help This option measures the time spent in irqs-off critical sections, with microsecond accuracy. The default measurement method is a maximum search, which is disabled by default and can be runtime (re-)started via: echo 0 > /sys/kernel/debug/tracing/tracing_max_latency (Note that kernel size and overhead increase with this option enabled. This option and the preempt-off timing option can be used together or separately.) config PREEMPT_TRACER bool "Preemption-off Latency Tracer" default n depends on PREEMPTION select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP select TRACE_PREEMPT_TOGGLE help This option measures the time spent in preemption-off critical sections, with microsecond accuracy. The default measurement method is a maximum search, which is disabled by default and can be runtime (re-)started via: echo 0 > /sys/kernel/debug/tracing/tracing_max_latency (Note that kernel size and overhead increase with this option enabled. This option and the irqs-off timing option can be used together or separately.) config SCHED_TRACER bool "Scheduling Latency Tracer" select GENERIC_TRACER select CONTEXT_SWITCH_TRACER select TRACER_MAX_TRACE select TRACER_SNAPSHOT help This tracer tracks the latency of the highest priority task to be scheduled in, starting from the point it has woken up. config HWLAT_TRACER bool "Tracer to detect hardware latencies (like SMIs)" select GENERIC_TRACER help This tracer, when enabled will create one or more kernel threads, depending on what the cpumask file is set to, which each thread spinning in a loop looking for interruptions caused by something other than the kernel. For example, if a System Management Interrupt (SMI) takes a noticeable amount of time, this tracer will detect it. This is useful for testing if a system is reliable for Real Time tasks. Some files are created in the tracing directory when this is enabled: hwlat_detector/width - time in usecs for how long to spin for hwlat_detector/window - time in usecs between the start of each iteration A kernel thread is created that will spin with interrupts disabled for "width" microseconds in every "window" cycle. It will not spin for "window - width" microseconds, where the system can continue to operate. The output will appear in the trace and trace_pipe files. When the tracer is not running, it has no affect on the system, but when it is running, it can cause the system to be periodically non responsive. Do not run this tracer on a production system. To enable this tracer, echo in "hwlat" into the current_tracer file. Every time a latency is greater than tracing_thresh, it will be recorded into the ring buffer. config MMIOTRACE bool "Memory mapped IO tracing" depends on HAVE_MMIOTRACE_SUPPORT && PCI select GENERIC_TRACER help Mmiotrace traces Memory Mapped I/O access and is meant for debugging and reverse engineering. It is called from the ioremap implementation and works via page faults. Tracing is disabled by default and can be enabled at run-time. See Documentation/trace/mmiotrace.rst. If you are not helping to develop drivers, say N. config ENABLE_DEFAULT_TRACERS bool "Trace process context switches and events" depends on !GENERIC_TRACER select TRACING help This tracer hooks to various trace points in the kernel, allowing the user to pick and choose which trace point they want to trace. It also includes the sched_switch tracer plugin. config FTRACE_SYSCALLS bool "Trace syscalls" depends on HAVE_SYSCALL_TRACEPOINTS select GENERIC_TRACER select KALLSYMS help Basic tracer to catch the syscall entry and exit events. config TRACER_SNAPSHOT bool "Create a snapshot trace buffer" select TRACER_MAX_TRACE help Allow tracing users to take snapshot of the current buffer using the ftrace interface, e.g.: echo 1 > /sys/kernel/debug/tracing/snapshot cat snapshot config TRACER_SNAPSHOT_PER_CPU_SWAP bool "Allow snapshot to swap per CPU" depends on TRACER_SNAPSHOT select RING_BUFFER_ALLOW_SWAP help Allow doing a snapshot of a single CPU buffer instead of a full swap (all buffers). If this is set, then the following is allowed: echo 1 > /sys/kernel/debug/tracing/per_cpu/cpu2/snapshot After which, only the tracing buffer for CPU 2 was swapped with the main tracing buffer, and the other CPU buffers remain the same. When this is enabled, this adds a little more overhead to the trace recording, as it needs to add some checks to synchronize recording with swaps. But this does not affect the performance of the overall system. This is enabled by default when the preempt or irq latency tracers are enabled, as those need to swap as well and already adds the overhead (plus a lot more). config TRACE_BRANCH_PROFILING bool select GENERIC_TRACER choice prompt "Branch Profiling" default BRANCH_PROFILE_NONE help The branch profiling is a software profiler. It will add hooks into the C conditionals to test which path a branch takes. The likely/unlikely profiler only looks at the conditions that are annotated with a likely or unlikely macro. The "all branch" profiler will profile every if-statement in the kernel. This profiler will also enable the likely/unlikely profiler. Either of the above profilers adds a bit of overhead to the system. If unsure, choose "No branch profiling". config BRANCH_PROFILE_NONE bool "No branch profiling" help No branch profiling. Branch profiling adds a bit of overhead. Only enable it if you want to analyse the branching behavior. Otherwise keep it disabled. config PROFILE_ANNOTATED_BRANCHES bool "Trace likely/unlikely profiler" select TRACE_BRANCH_PROFILING help This tracer profiles all likely and unlikely macros in the kernel. It will display the results in: /sys/kernel/debug/tracing/trace_stat/branch_annotated Note: this will add a significant overhead; only turn this on if you need to profile the system's use of these macros. config PROFILE_ALL_BRANCHES bool "Profile all if conditionals" if !FORTIFY_SOURCE select TRACE_BRANCH_PROFILING help This tracer profiles all branch conditions. Every if () taken in the kernel is recorded whether it hit or miss. The results will be displayed in: /sys/kernel/debug/tracing/trace_stat/branch_all This option also enables the likely/unlikely profiler. This configuration, when enabled, will impose a great overhead on the system. This should only be enabled when the system is to be analyzed in much detail.endchoice config TRACING_BRANCHES bool help Selected by tracers that will trace the likely and unlikely conditions. This prevents the tracers themselves from being profiled. Profiling the tracing infrastructure can only happen when the likelys and unlikelys are not being traced. config BRANCH_TRACER bool "Trace likely/unlikely instances" depends on TRACE_BRANCH_PROFILING select TRACING_BRANCHES help This traces the events of likely and unlikely condition calls in the kernel. The difference between this and the "Trace likely/unlikely profiler" is that this is not a histogram of the callers, but actually places the calling events into a running trace buffer to see when and where the events happened, as well as their results. Say N if unsure. config BLK_DEV_IO_TRACE bool "Support for tracing block IO actions" depends on SYSFS depends on BLOCK select RELAY select DEBUG_FS select TRACEPOINTSLines 1–500 of 942. Load more
# SPDX-License-Identifier: GPL-2.0-only # # Architectures that offer an FUNCTION_TRACER implementation should # select HAVE_FUNCTION_TRACER: # config USER_STACKTRACE_SUPPORT bool config NOP_TRACER bool config HAVE_FUNCTION_TRACER bool help See Documentation/trace/ftrace-design.rst config HAVE_FUNCTION_GRAPH_TRACER bool help See Documentation/trace/ftrace-design.rst config HAVE_DYNAMIC_FTRACE bool help See Documentation/trace/ftrace-design.rst config HAVE_DYNAMIC_FTRACE_WITH_REGS bool config HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS bool config HAVE_DYNAMIC_FTRACE_WITH_ARGS bool help If this is set, then arguments and stack can be found from the pt_regs passed into the function callback regs parameter by default, even without setting the REGS flag in the ftrace_ops. This allows for use of regs_get_kernel_argument() and kernel_stack_pointer(). config HAVE_FTRACE_MCOUNT_RECORD bool help See Documentation/trace/ftrace-design.rst config HAVE_SYSCALL_TRACEPOINTS bool help See Documentation/trace/ftrace-design.rst config HAVE_FENTRY bool help Arch supports the gcc options -pg with -mfentry config HAVE_NOP_MCOUNT bool help Arch supports the gcc options -pg with -mrecord-mcount and -nop-mcount config HAVE_C_RECORDMCOUNT bool help C version of recordmcount available? config TRACER_MAX_TRACE bool config TRACE_CLOCK bool config RING_BUFFER bool select TRACE_CLOCK select IRQ_WORK config EVENT_TRACING select CONTEXT_SWITCH_TRACER select GLOB bool config CONTEXT_SWITCH_TRACER bool config RING_BUFFER_ALLOW_SWAP bool help Allow the use of ring_buffer_swap_cpu. Adds a very slight overhead to tracing when enabled. config PREEMPTIRQ_TRACEPOINTS bool depends on TRACE_PREEMPT_TOGGLE || TRACE_IRQFLAGS select TRACING default y help Create preempt/irq toggle tracepoints if needed, so that other parts of the kernel can use them to generate or add hooks to them. # All tracer options should select GENERIC_TRACER. For those options that are # enabled by all tracers (context switch and event tracer) they select TRACING. # This allows those options to appear when no other tracer is selected. But the # options do not appear when something else selects it. We need the two options # GENERIC_TRACER and TRACING to avoid circular dependencies to accomplish the # hiding of the automatic options. config TRACING bool select RING_BUFFER select STACKTRACE if STACKTRACE_SUPPORT select TRACEPOINTS select NOP_TRACER select BINARY_PRINTF select EVENT_TRACING select TRACE_CLOCK config GENERIC_TRACER bool select TRACING # # Minimum requirements an architecture has to meet for us to # be able to offer generic tracing facilities: # config TRACING_SUPPORT bool depends on TRACE_IRQFLAGS_SUPPORT depends on STACKTRACE_SUPPORT default y if TRACING_SUPPORT menuconfig FTRACE bool "Tracers" default y if DEBUG_KERNEL help Enable the kernel tracing infrastructure. if FTRACE config BOOTTIME_TRACING bool "Boot-time Tracing support" depends on TRACING select BOOT_CONFIG help Enable developer to setup ftrace subsystem via supplemental kernel cmdline at boot time for debugging (tracing) driver initialization and boot process. config FUNCTION_TRACER bool "Kernel Function Tracer" depends on HAVE_FUNCTION_TRACER select KALLSYMS select GENERIC_TRACER select CONTEXT_SWITCH_TRACER select GLOB select TASKS_RCU if PREEMPTION select TASKS_RUDE_RCU help Enable the kernel to trace every kernel function. This is done by using a compiler feature to insert a small, 5-byte No-Operation instruction at the beginning of every kernel function, which NOP sequence is then dynamically patched into a tracer call when tracing is enabled by the administrator. If it's runtime disabled (the bootup default), then the overhead of the instructions is very small and not measurable even in micro-benchmarks. config FUNCTION_GRAPH_TRACER bool "Kernel Function Graph Tracer" depends on HAVE_FUNCTION_GRAPH_TRACER depends on FUNCTION_TRACER depends on !X86_32 || !CC_OPTIMIZE_FOR_SIZE default y help Enable the kernel to trace a function at both its return and its entry. Its first purpose is to trace the duration of functions and draw a call graph for each thread with some information like the return value. This is done by setting the current return address on the current task structure into a stack of calls. config DYNAMIC_FTRACE bool "enable/disable function tracing dynamically" depends on FUNCTION_TRACER depends on HAVE_DYNAMIC_FTRACE default y help This option will modify all the calls to function tracing dynamically (will patch them out of the binary image and replace them with a No-Op instruction) on boot up. During compile time, a table is made of all the locations that ftrace can function trace, and this table is linked into the kernel image. When this is enabled, functions can be individually enabled, and the functions not enabled will not affect performance of the system. See the files in /sys/kernel/debug/tracing: available_filter_functions set_ftrace_filter set_ftrace_notrace This way a CONFIG_FUNCTION_TRACER kernel is slightly larger, but otherwise has native performance as long as no tracing is active. config DYNAMIC_FTRACE_WITH_REGS def_bool y depends on DYNAMIC_FTRACE depends on HAVE_DYNAMIC_FTRACE_WITH_REGS config DYNAMIC_FTRACE_WITH_DIRECT_CALLS def_bool y depends on DYNAMIC_FTRACE_WITH_REGS depends on HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS config FUNCTION_PROFILER bool "Kernel function profiler" depends on FUNCTION_TRACER default n help This option enables the kernel function profiler. A file is created in debugfs called function_profile_enabled which defaults to zero. When a 1 is echoed into this file profiling begins, and when a zero is entered, profiling stops. A "functions" file is created in the trace_stat directory; this file shows the list of functions that have been hit and their counters. If in doubt, say N. config STACK_TRACER bool "Trace max stack" depends on HAVE_FUNCTION_TRACER select FUNCTION_TRACER select STACKTRACE select KALLSYMS help This special tracer records the maximum stack footprint of the kernel and displays it in /sys/kernel/debug/tracing/stack_trace. This tracer works by hooking into every function call that the kernel executes, and keeping a maximum stack depth value and stack-trace saved. If this is configured with DYNAMIC_FTRACE then it will not have any overhead while the stack tracer is disabled. To enable the stack tracer on bootup, pass in 'stacktrace' on the kernel command line. The stack tracer can also be enabled or disabled via the sysctl kernel.stack_tracer_enabled Say N if unsure. config TRACE_PREEMPT_TOGGLE bool help Enables hooks which will be called when preemption is first disabled, and last enabled. config IRQSOFF_TRACER bool "Interrupts-off Latency Tracer" default n depends on TRACE_IRQFLAGS_SUPPORT select TRACE_IRQFLAGS select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP help This option measures the time spent in irqs-off critical sections, with microsecond accuracy. The default measurement method is a maximum search, which is disabled by default and can be runtime (re-)started via: echo 0 > /sys/kernel/debug/tracing/tracing_max_latency (Note that kernel size and overhead increase with this option enabled. This option and the preempt-off timing option can be used together or separately.) config PREEMPT_TRACER bool "Preemption-off Latency Tracer" default n depends on PREEMPTION select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP select TRACE_PREEMPT_TOGGLE help This option measures the time spent in preemption-off critical sections, with microsecond accuracy. The default measurement method is a maximum search, which is disabled by default and can be runtime (re-)started via: echo 0 > /sys/kernel/debug/tracing/tracing_max_latency (Note that kernel size and overhead increase with this option enabled. This option and the irqs-off timing option can be used together or separately.) config SCHED_TRACER bool "Scheduling Latency Tracer" select GENERIC_TRACER select CONTEXT_SWITCH_TRACER select TRACER_MAX_TRACE select TRACER_SNAPSHOT help This tracer tracks the latency of the highest priority task to be scheduled in, starting from the point it has woken up. config HWLAT_TRACER bool "Tracer to detect hardware latencies (like SMIs)" select GENERIC_TRACER help This tracer, when enabled will create one or more kernel threads, depending on what the cpumask file is set to, which each thread spinning in a loop looking for interruptions caused by something other than the kernel. For example, if a System Management Interrupt (SMI) takes a noticeable amount of time, this tracer will detect it. This is useful for testing if a system is reliable for Real Time tasks. Some files are created in the tracing directory when this is enabled: hwlat_detector/width - time in usecs for how long to spin for hwlat_detector/window - time in usecs between the start of each iteration A kernel thread is created that will spin with interrupts disabled for "width" microseconds in every "window" cycle. It will not spin for "window - width" microseconds, where the system can continue to operate. The output will appear in the trace and trace_pipe files. When the tracer is not running, it has no affect on the system, but when it is running, it can cause the system to be periodically non responsive. Do not run this tracer on a production system. To enable this tracer, echo in "hwlat" into the current_tracer file. Every time a latency is greater than tracing_thresh, it will be recorded into the ring buffer. config MMIOTRACE bool "Memory mapped IO tracing" depends on HAVE_MMIOTRACE_SUPPORT && PCI select GENERIC_TRACER help Mmiotrace traces Memory Mapped I/O access and is meant for debugging and reverse engineering. It is called from the ioremap implementation and works via page faults. Tracing is disabled by default and can be enabled at run-time. See Documentation/trace/mmiotrace.rst. If you are not helping to develop drivers, say N. config ENABLE_DEFAULT_TRACERS bool "Trace process context switches and events" depends on !GENERIC_TRACER select TRACING help This tracer hooks to various trace points in the kernel, allowing the user to pick and choose which trace point they want to trace. It also includes the sched_switch tracer plugin. config FTRACE_SYSCALLS bool "Trace syscalls" depends on HAVE_SYSCALL_TRACEPOINTS select GENERIC_TRACER select KALLSYMS help Basic tracer to catch the syscall entry and exit events. config TRACER_SNAPSHOT bool "Create a snapshot trace buffer" select TRACER_MAX_TRACE help Allow tracing users to take snapshot of the current buffer using the ftrace interface, e.g.: echo 1 > /sys/kernel/debug/tracing/snapshot cat snapshot config TRACER_SNAPSHOT_PER_CPU_SWAP bool "Allow snapshot to swap per CPU" depends on TRACER_SNAPSHOT select RING_BUFFER_ALLOW_SWAP help Allow doing a snapshot of a single CPU buffer instead of a full swap (all buffers). If this is set, then the following is allowed: echo 1 > /sys/kernel/debug/tracing/per_cpu/cpu2/snapshot After which, only the tracing buffer for CPU 2 was swapped with the main tracing buffer, and the other CPU buffers remain the same. When this is enabled, this adds a little more overhead to the trace recording, as it needs to add some checks to synchronize recording with swaps. But this does not affect the performance of the overall system. This is enabled by default when the preempt or irq latency tracers are enabled, as those need to swap as well and already adds the overhead (plus a lot more). config TRACE_BRANCH_PROFILING bool select GENERIC_TRACER choice prompt "Branch Profiling" default BRANCH_PROFILE_NONE help The branch profiling is a software profiler. It will add hooks into the C conditionals to test which path a branch takes. The likely/unlikely profiler only looks at the conditions that are annotated with a likely or unlikely macro. The "all branch" profiler will profile every if-statement in the kernel. This profiler will also enable the likely/unlikely profiler. Either of the above profilers adds a bit of overhead to the system. If unsure, choose "No branch profiling". config BRANCH_PROFILE_NONE bool "No branch profiling" help No branch profiling. Branch profiling adds a bit of overhead. Only enable it if you want to analyse the branching behavior. Otherwise keep it disabled. config PROFILE_ANNOTATED_BRANCHES bool "Trace likely/unlikely profiler" select TRACE_BRANCH_PROFILING help This tracer profiles all likely and unlikely macros in the kernel. It will display the results in: /sys/kernel/debug/tracing/trace_stat/branch_annotated Note: this will add a significant overhead; only turn this on if you need to profile the system's use of these macros. config PROFILE_ALL_BRANCHES bool "Profile all if conditionals" if !FORTIFY_SOURCE select TRACE_BRANCH_PROFILING help This tracer profiles all branch conditions. Every if () taken in the kernel is recorded whether it hit or miss. The results will be displayed in: /sys/kernel/debug/tracing/trace_stat/branch_all This option also enables the likely/unlikely profiler. This configuration, when enabled, will impose a great overhead on the system. This should only be enabled when the system is to be analyzed in much detail. endchoice config TRACING_BRANCHES bool help Selected by tracers that will trace the likely and unlikely conditions. This prevents the tracers themselves from being profiled. Profiling the tracing infrastructure can only happen when the likelys and unlikelys are not being traced. config BRANCH_TRACER bool "Trace likely/unlikely instances" depends on TRACE_BRANCH_PROFILING select TRACING_BRANCHES help This traces the events of likely and unlikely condition calls in the kernel. The difference between this and the "Trace likely/unlikely profiler" is that this is not a histogram of the callers, but actually places the calling events into a running trace buffer to see when and where the events happened, as well as their results. Say N if unsure. config BLK_DEV_IO_TRACE bool "Support for tracing block IO actions" depends on SYSFS depends on BLOCK select RELAY select DEBUG_FS select TRACEPOINTS