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 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
"[<function name>@<filename>:<line number>]"
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
