[PATCH 1/3] Documention for trace records (trec).

[Wink Saville]

Trec is a light weight tracing mechanism that places
trace information into a buffer. The contents of the
buffer is dumped when errors occurs or when enabled
via SYSRQ commands.

Signed-off-by: Wink Saville <wink@xxxxxxxxxxx>
---
 Documentation/trec.txt |   87 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 87 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/trec.txt

diff --git a/Documentation/trec.txt b/Documentation/trec.txt
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+Title	: Trace Records
+Authors	: Wink Saville <wink@xxxxxxxxxxx>
+
+CONTENTS
+
+1. Concepts
+2. Architectures Supported
+3. Configuring
+4. API Reference
+5. Overhead
+6. TODO
+
+
+1. Concepts
+
+Trace records are a light weight tracing technique that time stamps
+small amounts of information and stores them in a buffer. TREC's are
+light enough that they may be sprinkled most anywhere in the kernel
+and have very little performance impact.
+
+For instance they can be placed in the scheduler and ISR's to watch
+the interaction between ISR's and the scheduler. They can be placed
+in memory handling routines to determine how and when memory is
+allocated and freed.
+
+In the current default configuration the trec's are dumped by calling
+trec_print_snapshot when die() or panic() are called as well as when
+the kernel itself page faults in do_page_fault.
+
+If CONFIG_MAGIC_SYSRQ is the 'y' command will execute trec_snapshot
+and the 'z' command will print the current snapshot.
+
+A general macro TREC allows trec_write to be invoked as a macro and
+TRECC allows it to be invoked conditionally. See include/linux/trec.h
+for the current set of macros.
+
+2. Architectures Supported
+
+Should support all architectures has been tested only on:
+
+- X86_64
+
+
+3. Configuring
+
+Since trec's are implemented as a device driver they are configured
+by enabling support in the "Device Drivers" section of as they could
+be used early being a module is not supported.
+
+
+4. API Reference
+
+Trec supports the following API:
+
+void trec_init(void):
+
+  Initialize the module, this may be called before the driver is loaded
+  if it is desired to use trec's early.
+
+void trec_write(unsigned long pc, int pid, unsigned long v1, unsigned long v2);
+
+  This is the routine used to write into the buffer. pc is the program counter
+  pid is the process id and v1 and v2 are two parameters.
+
+void trec_snapshot(void);
+
+  Calling this function takes a snapshot of the current trec buffer so that it
+  will not be modified. This is called prior to printing the snapshot via
+  trec_print_snapshot.
+
+void trec_print_snapshot(void);
+
+  Print the snapshot.
+
+5. Overhead
+
+Measured on a 2.4GHZ Core 2 Duo the readings between two TREC's is
+270 tics of the rdtsc or about 0.1us. No attempt has been made to
+optimize and less information can be collected if the overhead
+is still to high.
+
+
+6. TODO
+
+a. Add code to dump trec to user space
+b. Enhance to allow runtime registration and runtime enable disable.
+
-- 
1.5.0.rc2

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