+++ /dev/null
-
-Mathieu Desnoyers -- November 2005
-
-This is a complete rework of genevent.
-
-The 'genevent' program parses event descriptions and generates
-the inline functions to record events in the kernel.
-
-There are several files in the directory:
- genevent.c, genevent.h, crc32.tab, parser.c and parser.h
-
-In fact, crc32.tab, parser.c and parser.h are the same files as
-those in LTT library.
-
-Important notes :
- * Do not put "-" symbols in facilities name.
- * Use the exact same name for facility xml file and for facility name.
- * As from genevent 0.17, a standard XML 1.0 description is "required". It must
- begin with the <?xml version="1.0"?> header.
-
-Note about strings :
-There are three methods to write strings in genevent, each suitable and
-efficient for a particular case. They are explained here from the fastest
-to the slowest.
-1 - The C code presents a fixed size string.
- For example, you find :
- char mystring[10];
- as string definition.
-
- you must then define it as an array of char :
- <array size="10"><char></array>
-
- Note, however, that you might not want to declare a fixed size for trace size
- and unnecessary copy matters.
-
- For instance, on a 32 bits architecture, copying a n bytes array takes
- approximately* n/4 memory read and write, for n/2 memory operations.
-
- Using the slower method described in (3), with a strlen and memcpy, where
- "u" is the number of used caracters, takes u+1 reads for the strlen, and
- approximately* (u+1)/4 read and write for the memcpy, for a total of :
- (3/2)*(u+1) memory access.
-
- So, if (n/2) > (3/2)*(u+1), or : n > 3*u+3
- where n is the size of the array
- u is the average number of used caracters (excluding the \0)
- it becomes faster to use the method number 3 with strlen.
-
-2 - The C code presents a variable size string together with its
- size.
-
- A typical use for this case is filenames in the Linux kernel. The
- dentry strucure has a d_name member, which is a struct qstr containing
- a unsigned int len and const unsigned char *name.
-
- you must use a sequence to declare this efficiently :
- <sequence><uint><char></sequence>
-
-3 - The C code presents a \0 terminated string.
-
- This is the slowest, but most convenient way to declare a string. You are
- discouraged to use it when options 1 or 2 are available. It will dynamically
- calculate the string length (byte by byte read) and only afterward do a
- memcpy.
-
- Note that, as explained in 1, if n > 3*u+3, it becomes faster to use this
- method instead of copying the whole fixed size array.
-
- Declare like this :
- <string>
-
-Here is a brief description of how to use genevent.
-
-make
-make install
-
-
-* Add new events to the kernel with genevent
-
-su -
-cd /usr/local/share/LinuxTraceToolkitViewer/facilities
-cp process.xml yourfacility.xml
- * edit yourfacility.xml to fit your needs.
-cd /tmp
-/usr/local/bin/genevent /usr/local/share/LinuxTraceToolkitViewer/yourfacility.xml
-cp ltt-facility-yourfacility.h ltt-facility-id-yourfacility.h \
- /usr/src/linux-2.6.12-rc4-mm2-lttng-0.2/include/linux/ltt
-cp ltt-facility-loader-yourfacility.c ltt-facility-loader-yourfacility.h \
- /usr/src/linux-2.6.12-rc4-mm2-lttng-0.2/ltt
- * edit the kernel file you want to instrument
- - Add #include <linux/ltt/ltt-facility-yourfacility.h> at the beginning
- of the file.
- - Add a call to the tracing functions. See their names and parameters in
- /usr/src/linux-2.6.12-rc4-mm2-lttng-0.2/include/linux/ltt/ltt-facility-yourfacility.h
-
-
-
-* The approximation comes from the fact that copies of number of caracters non
- multiple of the architecture size takes more operations (maximum of :
- (architecture size (in bytes) - 1) operations).
-
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