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This patch creates a new character device, uncachedev.
Pages of RAM allocated by this device are not cached by
CPUs.
Uses for such pages:
1) Determining *very* pessimistic emperical worst-
case execution times.
2) Compare against performance with caches (quantify
the avg. case benefit).
3) Deterministic memory accesses (access cannot cause a
cache eviction.)
4) Theoretically, increased performance can be achieved
by storing infrequently accessed data in uncache pages.
uncachedev allocates pages with the pgprot_noncached() page
attribute for user applications. Since pages allocated by
uncachedev are not locked in memory by default, applications
with any access level may mmap pages with uncachedev.
Limitations:
1) Uncache pages must be MAP_PRIVATE.
2) Remapping not supported.
Usage (user level):
int size = NR_PAGES*PAGE_SIZE;
int fd = open("/dev/litmus/uncache", O_RDWR);
char *data = mmap(NULL, size, PROT_READ | PROT_WRITE,
MAP_PRIVATE, fd, 0);
<...do stuff...>
munmap(data, size);
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If a task is released on a CPU that is idle, then it is pointless to
send an IPI to another CPU just to schedule the newly released task.
This patch changes check_for_preemptions() to prefer the local CPU
first if it is idle.
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If !CONFIG_SCHED_TASK_TRACE, but CONFIG_SCHED_LITMUS_TRACEPOINT, then
we still need to define the tracepoint structures.
This patch should be integrated with the earlier sched_task_trace.c
patches during one of the next major rebasing efforts.
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This patch adds the core of LITMUS^RT:
- library functionality (heaps, rt_domain, prioritization, etc.)
- budget enforcement logic
- job management
- system call backends
- virtual devices (control page, etc.)
- scheduler plugin API (and dummy plugin)
This code compiles, but is not yet integrated with the rest of Linux.
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This patch integrates LITMUS^RT's sched_trace_XXX() macros with
Linux's notion of tracepoints. This is useful to visualize schedules
in kernel shark and similar tools. Historically, LITMUS^RT's
sched_trace predates Linux's tracepoint infrastructure.
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This patch introduces the sched_trace infrastructure, which in
principle allows tracing the generated schedule. However, this patch
does not yet integrate the callbacks with the kernel.
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This patch exports the interrupt counter to userspace via the control
page.
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This patch adds support for tracing release latency in LITMUS^RT.
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Remove dummy implementation of is_realtime() in trace.c.
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This patch adds the infrastructure for the TRACE() debug macro.
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This patch adds the main infrastructure for tracing overheads in
LITMUS^RT. It does not yet introduce any tracepoints into the kernel.
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This patch adds the ftdev device driver, which is used to export
samples collected with Feather-Trace to userspace.
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This patch adds the x86-specific implementation of Feather-Trace
triggers that works by rewriting jump instructions.
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This patch adds the simple fallback implementation and creates dummy
hooks in the x86 and ARM Kconfig files.
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Hookup litmus/ with kernel and add extra version.
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