A performance tuning utility for improving execution time and real memory utilization of user-level application programs.
fdpr -p Program -x Command
fdpr -p Program [-M Segnum ] [-o OutputFile ] [-nI ] [[-Rn ]|[-R0 |-R1 |-R2 |-R3 ]] [-v ] -s [-1 |-3 ] [-x Command ]
fdpr -p Program [-M Segnum ] [-o OutputFile ] [-nI ] [[-Rn ]|[-R0 |-R1 |-R2 |-R3 ]] [-v ] [-s [-2 |-12|-23] -x Command
The fdpr command (Feedback Directed Program Restructuring) is a performance-tuning utility which may help improve the execution time and the real memory utilization of user-level application programs. The fdpr program optimizes the executable image of a program by collecting information on the behavior of the program while the program is used for some typical workload, and then creating a new version of the program which is optimized for that workload. The new program generated by fdpr will typically run faster and use less real memory.
Attention: The fdpr command applies advanced optimization techniques to a program which may result in programs that do not behave as expected; programs which are reordered using this tool should be used with due caution and should be rigorously retested with, at a minimum, the same test suite used to test the original program in order to verify expected functionality. The reordered program is not supported.
The fdpr command builds an optimized executable program in 3 distinct phases:
These phases can be run separately or in partial or full combination, but must be run in order (i.e., -1 then -2 then -3 or -12 then -3) and by the same user. The default is to run all three phases.
Note: The instrumented executable, created in phase 1 and run in phase 2, typically runs several times slower than the original program. Due to the increased execution time required by the instrumented program, the executable should be invoked in such a way as to minimize execution duration, while still fully exercising the desired code areas. The fdpr command user should also attempt to eliminate, where feasible, any time dependent aspects of the program.
Note: The -Rn flag cannot be used with the and -R0 , -R1, -R2, -R3 flags.
Note: The -R2 and -R0 flags do not support programs which were compiled with the -g flag.
The fdpr command provides four levels of optimization. The flags -R1, -R2, and -R3 provide the most aggressive optimization along with the greatest potential speedups. However, in some cases, using these optimization levels may result in an executable which does not behave as expected. Programs which contain assembler code (in particular code which performs dynamic branch calculations) or programs derived from nonstandard compilers are prone to these types of reordering-induced anomalies. In addition, the -R1 and -R3 flags produce executables which do not include debug information and are therefore not supported by the dbx command.
Use of the -R0 flag may result in a slightly reduced performance improvement as this flag attempts to preserve functionality and debug capability by maintaining the original program structure and by eliminating branch table and function descriptor pointer adjustments. Functional errors are much less likely, though still possible. Also, this option will produce a reordered executable which is typically 20-40% larger than the original program.
Both the -R0 and -R2 flags utilize a program-reordering technique in which the original structure of the program, including traceback entries, is preserved. The reordered code, which represents the highly-executed code paths through the program, is appended to the end of the executable. This technique provides near optimal performance improvement by allowing global code reordering (independent of procedure boundaries and absent of interleaved traceback entries) while preserving the debug capability. In addition, program functionality is maintained for a larger class of programs using the original program structure as a "safety net" to catch undetected and/or unmodified dynamically (runtime) computed branch instructions). The -R2 flag attempts to fix all dynamically computed branches which branch to moved code. However, for some programs (especially assembler programs) it is difficult to correctly identify these dynamic branches and using the -R2 flag for this class of programs may result in unexpected functional errors. Also, reordering programs which utilize any form of self`-modifying code will probably result in unexpected functional errors.
Executables built with the -qfdpr compiler flag contain information to assist fdpr in producing reordered programs with guaranteed functionality. When this compiler flag is used, the functionality advantage of fdpr option -R0 is extended to options -R1, -R2, and -R3. However, if -qfdpr is used, only those object modules built with this flag will be reordered. If the -qfdpr flag is used, it should be used for all object modules in a program. Static linking will not improve performance if the -qfdpr flag is used.
Additional performance enhancements may be realized by using static linking when building the program to be reordered. Since the fdpr program only reorders the instructions within the executable program specified, any dynamically linked shared library routines called by the program are not reordered. Statically linking these library routines to the executable allows for reordering both the instructions in the program and all library routines used by the program. There are other advantages as well as disadvantages to building a statically linked program. See "Dynamic and Static Linking" in the AIX Versions 3.2 and 4 Performance Tuning Guide for further information.
All files created by the fdpr command are stored in the current directory with the exception of any files which may be created by running the command specified in the -x flag. During the optimization process, the original program is saved by renaming the program, and is only restored to the original program name upon successful completion of the final phase.
The profile file created by the fdpr command explicitly uses the name of the current directory since scripts used to run the program may change the working directory before executing the program.
The files created and/or used by the fdpr command are:
The use of the optimization flags -R0 and -R2 results in an executable which has additional information included in the program file for use by the dbx debug program. This additional information allows dbx to provide limited debug support by mapping reordered instruction addresses to their original locations and by maintaining traceback entries in the original text section. The dbx command maps most reordered instruction addresses to the corresponding addresses in the original executable as follows:
where 0xRRRRRRRR indicates the reordered address and fdpr[0xYYYYYYYY] indicates the original address. Also, dbx uses the traceback entries in the original instruction area to find associated procedure names and during stack traceback. See the "Examples" section for further details.
The following are typical usage examples of the fdpr command.
test2 script file: # code to exercise test1 test1 -expand 100 -root $PATH file.jpg -quit # the end of test2Run the fdpr command (using the default optimization):
fdpr -p test1 -x test2This results in the new reordered executable test1.fdpr.
fdpr -s -1 -p test1This command string renames the original program to __test1.save and creates an instrumented version with the name test1 .
To execute phase two and save temporary files.
fdpr -s -2 -p test1 -x test2This command string executes the script file test2 which runs the instrumented version of test1 to collect the profile data.
To execute phase three, saving temporary files.
fdpr -s -3 -p test1Again, this results in the new reordered executable test1.fdpr.
fdpr -s -12 -p test1 -x test2Execute phase three, while saving temporary files and using optimization level three.
fdpr -s -3 -R3 -p test1
dbx program.fdprwhich produces the output simular to the following:
Type 'help' for help. reading symbolic information ...warning: no source compiled with -g [using memory image in core] Segmentation fault in proc_d at 0x10000634 = fdpr[0x10000290] 0x10000634 (???) 98640000 stb r3,0x0(r4) (dbx)The address mapping information 0x10000634 = fdpr[0x10000290] indicates that the instruction at address 0x10000634 is in the reordered text section and originally resided (in the original program) at address 0x10000290 in proc_d . Running dbx on the original program and using the mapped addresses (0x10000290 in the above example) may provide additional information to aid in debugging.
A stack traceback, which is used to determine how the program arrived at the current location, is produced as follows:
(dbx) wherewhich produces the following output:
proc_d(0x0) at 0x10000634 proc_c(0x0) at 0x10000604 proc_b(0x0) at 0x100005d0 proc_a(0x0) at 0x1000059c main(0x2, 0x2ff7fba4) at 0x1000055c (dbx)
(dbx) stepiwhich produces the following output:
stopped in proc_d at 0x1000061c = fdpr[0x10000278] 0x1000061c (???) 9421ffc0 stwu r1,-64(r1) (dbx)In this example dbx indicates that the program stopped in routine proc_d at address 0x1000061c in the reordered text section (originally located at address 0x10000278 ).
The dbx command.
Restructuring Executables with fdpr in AIX Versions 3.2 and 4 Performance Tuning Guide.