fdpr Command

Purpose

A performance tuning utility for improving execution time and real memory utilization of user-level post-link application programs.

Syntax

Most Common Usage:

fdpr -p ProgramFile -x WorkloadCommand

Detailed Usage:

fdpr -p ProgramFile [ -M SegNum ] [ -fd Fdesc ] [ -o OutputFile ] [ -armember ArchiveMemberList ] [ OptimizationFlags ] [ -map ] [ -disasm ] [ -disasm_data] [ -disasm_bss] [ -profcount ] [ -quiet] [ -v ] [ -1 | -2 | -3 | -12 | -23 | -123] [ -x WorkloadCommand ]

Optimization Flags

[ -tb ] [ -pc ] [ -pp ] [ -O ][ -O2 ] [ -O3 ] [ -O4 ] [ -selective_inline] [ -sid_fac percent] [ -inline_small_funcs size] [ -inline_hot_funcs percent] [ -hco_resched] [ -killed_regs ] [ -lr_opt] [ -align bytes] [ -RD ] [ -dpnf factor] [ -dpht threshold] [ -build_dcg] [ -tocload ] [-ptrgl_opt ] [ -no_ptrgl_r11] [ -dcbt_opt ] [ -ignore_info] [ -dead_code_removal] [ -bt_csect_anchor_removal] [ -strip] [-analyse_asm_csects] [-extra_safe_analysis] [-inline] [-reduce_toc removal_factor]

Description

The fdpr command (Feedback Directed Program Restructuring) is a performance-tuning utility that 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 that is optimized for that workload. The new program generated by fdpr typically runs faster and uses less real memory.

The fdpr command builds an optimized executable program in 3 distinct phases:

• Phase 1 (-1 flag): Creates an instrumented executable program and an empty template profile file.
• Phase 2 (-2 flag): Runs the instrumented program and updates the profile data.
• Phase 3 (-3 flag): Generates the optimized executable program file.

Flags

Optimization Flags

Optimization

The fdpr command performs, by default, the highest possible level of code reordering optimization together with the optimizations of branch prediction bit setting, branch folding, code alignment and removal of redundant NOOP instructions. The -pc flag reorders the entire code while preserving csects' boundaries and therefore, may result in less performance improvement than the default code reordering. Similarly, the -pp flag reorders the entire code while preserving procedures' boundaries.

Additional optimizations performed on the entire executable program file are available by the optimization flags above.

Executables built with the -qfdpr IBM® xl compiler flag contain information to assist fdpr in producing reordered programs. Modules which are not compiled with the -qfdpr option, are reordered based on the compiler signatures in the symbol table.

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 optimized. Statically linking these library routines to the executable allows for optimizing 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.

Output Files

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 workload 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 full 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:

Enhanced Debugging Capabilities

In order to enable a certain degree of debugging capability for optimized programs, FDPR updates the Symbol Table to reflect the changes that were made in the .text section.

Entry fields in the Symbol Table that specify addresses of symbols that were relocated during the reordering of FDPR, are modified to point to their new addresses in the .text section.

In addition, in the case where functions or files are split during reordering, FDPR creates new entries in the Symbol Table for each new part of the split function/file. These new parts of the same function are given new symbol names in the Symbol Table according to the following naming convention:

<original function name>__fdpr_<function's part number>

After code reordering all the new entries are suffixed with the __fdpr_ string.

  [Index] m   Value       Scn     Aux   Sclass    Type    Name
   [456]  m  0x00000230    2       1     0x02    0x0000   .main

  [Index] m   Value       Scn     Aux   Sclass    Type    Name
   [456]  m  0x00000304    2       1     0x02    0x0000   .main
  [1447]  m  0x00003328    2       1     0x02    0x0000   .main__fdpr_1
  [1453]  m  0x000033b4    2       1     0x02    0x0000   .main__fdpr_2

Examples

The following are typical usage examples of the fdpr command.

1. This example allows the user to run all three phases. In this example, test1 is the unstripped executable and test2 is a shell script that invokes test1. The current working directory is /tmp/fdpr.

   test2 script file:
   
   # code to exercise test1
   test1 -expand 100 -root $PATH file.jpg -quit
   # the end of test2

   Execute the fdpr command (using the default optimization):

   fdpr -p test1 -x test2

   This results in the new reordered executable test1.fdpr.
2. To run one phase at a time, execute phase one of fdpr.

   fdpr -1 -p test1

   This command string creates an instrumented version with the name test1.instr and the empty template profile file test1.nprof.

   To execute phase two:

   fdpr -2 -p test1 -x test2

   This command string executes the script file test2 that runs the instrumented version of test1 to collect the profile data.

   To execute phase three:

   fdpr -3 -p test1

   Again, this results in the new reordered executable test1.fdpr.
3. To run the first two phases followed by phase three, execute phase one and two.

   fdpr -12 -p test1 -x test2

   Execute phase three using optimization level three.

   fdpr -3 -O3 -p test1

4. If an error occurs while running an fdpr optimized program, the dbx command can be used to determine what procedure the error occurred in as follows:

   dbx program.fdpr

   which produces the output similar 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
   0x10000634 (???) 98640000        stb   r3,0x0(r4)
   (dbx)

   A stack traceback, which is used to determine how the program arrived at the current location, is produced as follows:

   (dbx) where

   which 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)

5. The dbx subcommand stepi may also be used to single step through the instructions of a reordered executable program as follows:

   (dbx) stepi

   which produces the following output:

   stopped in proc_d at 0x1000061c
   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.

Implementation Specifics

Software Product/Option: AIX® Performance Aide/ Local Performance Analysis & Control Commands.

Standards Compliance: None.

Files