menu "LITMUS^RT" menu "Tracing" config FEATHER_TRACE bool "Feather-Trace Infrastructure" depends on !RELOCATABLE default y help Feather-Trace basic tracing infrastructure. Includes device file driver and instrumentation point support. There are actually two implementations of Feather-Trace. 1) A slower, but portable, default implementation. 2) Architecture-specific implementations that rewrite kernel .text at runtime. If enabled, Feather-Trace will be based on 2) if available (currently only for x86). However, if DEBUG_RODATA=y, then Feather-Trace will choose option 1) in any case to avoid problems with write-protected .text pages. Bottom line: to avoid increased overheads, choose DEBUG_RODATA=n. Note that this option only enables the basic Feather-Trace infrastructure; you still need to enable SCHED_TASK_TRACE and/or SCHED_OVERHEAD_TRACE to actually enable any events. config SCHED_TASK_TRACE bool "Trace real-time tasks" depends on FEATHER_TRACE default y help Include support for the sched_trace_XXX() tracing functions. This allows the collection of real-time task events such as job completions, job releases, early completions, etc. This results in a small overhead in the scheduling code. Disable if the overhead is not acceptable (e.g., benchmarking). Say Yes for debugging. Say No for overhead tracing. config SCHED_TASK_TRACE_SHIFT int "Buffer size for sched_trace_xxx() events" depends on SCHED_TASK_TRACE range 8 13 default 9 help Select the buffer size of sched_trace_xxx() events as a power of two. These buffers are statically allocated as per-CPU data. Each event requires 24 bytes storage plus one additional flag byte. Too large buffers can cause issues with the per-cpu allocator (and waste memory). Too small buffers can cause scheduling events to be lost. The "right" size is workload dependent and depends on the number of tasks, each task's period, each task's number of suspensions, and how often the buffer is flushed. Examples: 12 => 4k events 10 => 1k events 8 => 512 events config SCHED_LITMUS_TRACEPOINT bool "Enable Event/Tracepoint Tracing for real-time task tracing" depends on TRACEPOINTS default n help Enable kernel-style events (tracepoint) for Litmus. Litmus events trace the same functions as the above sched_trace_XXX(), but can be enabled independently. Litmus tracepoints can be recorded and analyzed together (single time reference) with all other kernel tracing events (e.g., sched:sched_switch, etc.). This also enables a quick way to visualize schedule traces using trace-cmd utility and kernelshark visualizer. Say Yes for debugging and visualization purposes. Say No for overhead tracing. config SCHED_OVERHEAD_TRACE bool "Record timestamps for overhead measurements" depends on FEATHER_TRACE default y help Export event stream for overhead tracing. Say Yes for overhead tracing. config SCHED_OVERHEAD_TRACE_SHIFT int "Buffer size for Feather-Trace overhead data" depends on SCHED_OVERHEAD_TRACE range 15 32 default 22 help Select the buffer size for the Feather-Trace overhead tracing infrastructure (/dev/litmus/ft_trace0 & ftcat) as a power of two. The larger the buffer, the less likely the chance of buffer overflows if the ftcat process is starved by real-time activity. In machines with large memories, large buffer sizes are recommended. Examples: 16 => 2 MB 24 => 512 MB 26 => 2G MB config SCHED_DEBUG_TRACE bool "TRACE() debugging" default n help Include support for sched_trace_log_messageg(), which is used to implement TRACE(). If disabled, no TRACE() messages will be included in the kernel, and no overheads due to debugging statements will be incurred by the scheduler. Disable if the overhead is not acceptable (e.g. benchmarking). Say Yes for debugging. Say No for overhead tracing. config SCHED_DEBUG_TRACE_SHIFT int "Buffer size for TRACE() buffer" depends on SCHED_DEBUG_TRACE range 14 22 default 18 help Select the amount of memory needed per for the TRACE() buffer, as a power of two. The TRACE() buffer is global and statically allocated. If the buffer is too small, there will be holes in the TRACE() log if the buffer-flushing task is starved. The default should be sufficient for most systems. Increase the buffer size if the log contains holes. Reduce the buffer size when running on a memory-constrained system. Examples: 14 => 16KB 18 => 256KB 20 => 1MB This buffer is exported to usespace using a misc device as 'litmus/log'. On a system with default udev rules, a corresponding character device node should be created at /dev/litmus/log. The buffer can be flushed using cat, e.g., 'cat /dev/litmus/log > my_log_file.txt'. config SCHED_DEBUG_TRACE_CALLER bool "Include [function@file:line] tag in TRACE() log" depends on SCHED_DEBUG_TRACE default n help With this option enabled, TRACE() prepends "[@:]" to each message in the debug log. Enable this to aid in figuring out what was called in which order. The downside is that it adds a lot of clutter. If unsure, say No. endmenu endmenu