menu "LITMUS^RT" menu "Scheduling" config RELEASE_MASTER bool "Release-master Support" depends on ARCH_HAS_SEND_PULL_TIMERS && SMP default n help Allow one processor to act as a dedicated interrupt processor that services all timer interrupts, but that does not schedule real-time tasks. See RTSS'09 paper for details (http://www.cs.unc.edu/~anderson/papers.html). config PREFER_LOCAL_LINKING bool "Link newly arrived tasks locally if possible" depends on SMP default y help In linking-based schedulers such as GSN-EDF, if an idle CPU processes a job arrival (i.e., when a job resumed or was released), it can either link the task to itself and schedule it immediately (to avoid unnecessary scheduling latency) or it can try to link it to the CPU where it executed previously (to maximize cache affinity, at the expense of increased latency due to the need to send an IPI). In lightly loaded systems, this option can significantly reduce scheduling latencies. In heavily loaded systems (where CPUs are rarely idle), it will likely make hardly a difference. If unsure, say yes. config LITMUS_QUANTUM_LENGTH_US int "quantum length (in us)" default 1000 range 500 10000 help Determine the desired quantum length, in microseconds, which is used to determine the granularity of scheduling in quantum-driven plugins (primarily PFAIR). This parameter does not affect event-driven plugins (such as the EDF-based plugins and P-FP). Default: 1000us = 1ms. config BUG_ON_MIGRATION_DEADLOCK bool "Panic on suspected migration deadlock" default y help This is a debugging option. The LITMUS^RT migration support code for global scheduling contains a simple heuristic to detect when the system deadlocks due to circular stack dependencies. For example, such a deadlock exists if CPU 0 waits for task A's stack to become available while using task B's stack, and CPU 1 waits for task B's stack to become available while using task A's stack. Such a situation can arise in (buggy) global scheduling plugins. With this option enabled, such a scenario with result in a BUG(). You can turn off this option when debugging on real hardware (e.g., to rescue traces, etc. that would be hard to get after a panic). Only turn this off if you really know what you are doing. If this BUG() triggers, the scheduler is broken and turning off this option won't fix it. endmenu menu "Real-Time Synchronization" config NP_SECTION bool "Non-preemptive section support" default y help Allow tasks to become non-preemptable. Note that plugins still need to explicitly support non-preemptivity. Currently, only the GSN-EDF, PSN-EDF, and P-FP plugins have such support. This is required to support locking protocols such as the FMLP. If disabled, all tasks will be considered preemptable at all times. config LITMUS_LOCKING bool "Support for real-time locking protocols" depends on NP_SECTION default y help Enable LITMUS^RT's multiprocessor real-time locking protocols with predicable maximum blocking times. Say Yes if you want to include locking protocols such as the FMLP and Baker's SRP. endmenu menu "Performance Enhancements" config SCHED_CPU_AFFINITY bool "Local Migration Affinity" depends on X86 && SYSFS default y help Rescheduled tasks prefer CPUs near to their previously used CPU. This may improve cache performance through possible preservation of cache affinity, at the expense of (slightly) more involved scheduling logic. Warning: May make bugs harder to find since tasks may migrate less often. NOTES: * Feature is not utilized by PFair/PD^2. Say Yes if unsure. config ALLOW_EARLY_RELEASE bool "Allow Early Releasing" default y help Allow tasks to release jobs early (while still maintaining job precedence constraints). Only supported by EDF schedulers. Early releasing must be explicitly requested by real-time tasks via the task_params passed to sys_set_task_rt_param(). Early releasing can improve job response times while maintaining real-time correctness. However, it can easily peg your CPUs since tasks never suspend to wait for their next job. As such, early releasing is really only useful in the context of implementing bandwidth servers, interrupt handling threads, or short-lived computations. Beware that early releasing may affect real-time analysis if using locking protocols or I/O. Say Yes if unsure. choice prompt "EDF Tie-Break Behavior" default EDF_TIE_BREAK_LATENESS_NORM help Allows the configuration of tie-breaking behavior when the deadlines of two EDF-scheduled tasks are equal. config EDF_TIE_BREAK_LATENESS bool "Lateness-based Tie Break" help Break ties between two jobs, A and B, based upon the lateness of their prior jobs. The job with the greatest lateness has priority. Note that lateness has a negative value if the prior job finished before its deadline. config EDF_TIE_BREAK_LATENESS_NORM bool "Normalized Lateness-based Tie Break" help Break ties between two jobs, A and B, based upon the lateness, normalized by relative deadline, of their prior jobs. The job with the greatest normalized lateness has priority. Note that lateness has a negative value if the prior job finished before its deadline. Normalized lateness tie-breaks are likely desireable over non-normalized tie-breaks if the execution times and/or relative deadlines of tasks in a task set vary greatly. config EDF_TIE_BREAK_HASH bool "Hash-based Tie Breaks" help Break ties between two jobs, A and B, with equal deadlines by using a uniform hash; i.e.: hash(A.pid, A.job_num) < hash(B.pid, B.job_num). Job A has ~50% of winning a given tie-break. config EDF_PID_TIE_BREAK bool "PID-based Tie Breaks" help Break ties based upon OS-assigned thread IDs. Use this option if required by algorithm's real-time analysis or per-task response-time jitter must be minimized. NOTES: * This tie-breaking method was default in Litmus 2012.2 and before. endchoice endmenu 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. config PREEMPT_STATE_TRACE bool "Trace preemption state machine transitions" depends on SCHED_DEBUG_TRACE && DEBUG_KERNEL default n help With this option enabled, each CPU will log when it transitions states in the preemption state machine. This state machine is used to determine how to react to IPIs (avoid races with in-flight IPIs). Warning: this creates a lot of information in the debug trace. Only recommended when you are debugging preemption-related races. If unsure, say No. endmenu endmenu