Signed-off-by: Wink Saville <[EMAIL PROTECTED]> --- 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 new file mode 100644 index 0000000..e12a552 --- /dev/null +++ b/Documentation/trec.txt @@ -0,0 +1,87 @@ +Title : Trace Records +Authors : Wink Saville <[EMAIL PROTECTED]> + +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. + + +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. + +In addition a set of macros are defined for convience, they come in +two flavors, TRECxxx and ZRECxxx. The TRECxxx macros invoke trec_write +and the ZRECxxx macros do nothing allowing the macros to be quicly +disabled. Look at include/linux/trec.h for the current set of macros. + + +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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
