debug and tunning

linux debugging and performance tunning

LTT linux trace toolkits for summery

date;ps;date

time 命令可以用來測量實際啟動並執行時間

gettimeofday return seconds and microseconds

profile就是用來看花費在subroutine或者func上面的時間

grof

Beforeprograms can be profiled using gprof, they must be compiled with the -pg gcc option.

$ gcc –pg –o sample1sample1.c

Thesample1 program prints the prime numbers up to 50,000.Whenthe sample1 program is run, the gmon.out file is created $gprof-b ./sample1–The -b optioneliminates the text output that explains the data output provided by gprofYoucan use the output from gprof to increase this program's performance by changingthe code to perform faster

#include<stdlib.h>

#include<stdio.h>

int prime (int num);

 int main()

 {

    int i;

    int colcnt = 0;

    for (i=2; i <= 50000; i++)

         if (prime(i)) {

  colcnt++;

       if (colcnt%9 == 0) {

      printf("%5d\n",i);

      colcnt =0;

          } else

            printf("%5d", i);

         }

    putchar('\n');

    return 0;

}

 intprime (int num)

 {

    /* check to see if the number is a prime? */

    inti;

    for (i=2; i < num; i++)

         if (num %i == 0)

  return 0;

         return 1;

 }

Nextwe can use the gcov program to look at the actual number of times eachline of the program was executed (See Chapter 2)Buildthe sample1 program with two additional options :

$ gcc -pg -fprofile-arcs -ftest-coverage -o sample1sample1.c

Runningsample1 and creating gcov output./sample1gcov sample1.cRunninggcovon the source code produces the file sample1.c.gcov. It shows the actual number of times each line ofthe program was executed

oprofile tools

A performancecounter is the part of a microprocessor that measures and gathersperformance-relevant events on the microprocessor.The numberand type of available events differ significantly between existingmicroprocessors.These counters imposeno overheadon the systemOne performance area ofconcern is cache misses.The following section describes different types of coding areas that can causecache misses

Cache missesare costly, try to minimize by following suggestions: Keep frequentlyaccessed data together. Storeand access frequently used data in flat, sequential data structuresand avoid pointer indirection.Access data sequentially. If theprogram is accessing data sequentially, each cache miss brings in n words. Ifthe program is accessing only nth word, it brings in unneeded data, degradingperformance.Avoid simultaneously traversing several large buffers of dataTherecan be cache conflicts between the buffers. Instead, pack the contentssequentially into one buffer whenever possible. If you are using vertex arrays,try to use interleaved arrays.Some framebuffers have cache-likebehaviors as well. It isa good idea to group geometry so that the drawing is done to one part of thescreen at a time.

Padding

Some compilers (or compiler options) automatically pad structures.Referencinga data structure that spans two cache blocks may incur two misses, even if thestructure itself is smaller than the block size.Paddingstructures to a multiple of the block size and aligning them on a blockboundary can eliminate these "misalignment" misses

Aligning

Alignment is a little more difficult, since the structure'saddress must be a multiple of the cache block size.Aligningstatically declared structures generally requires compiler support. Some versions of malloc() return cache block aligned memoryTheprogrammer can align dynamically allocated structures using simple pointerarithmetic

Packing

Packing is the opposite of paddingBy packingan array into the smallest space possible, the programmer increases locality,which can reduce both conflict and capacitymisses.

Loop Grouping

Numericprograms often consist of several operations on the same data, coded as multipleloops over the same arraysCombining these loops may increases the program's temporallocality and frequently reduces the number of capacity misses

ophelp

oprofile - http://oprofile.sourceforge.net/Prospect - http://sourceforge.net/projects/prospectAMD64 SoftwareOptimization Guide –

http://www.amd.com/us-en/assets/content_type/DownloadableAssets/dwamd_25112.pdfIntel ArchitectureOptimization Reference Manual -
http://developer.intel.com/design/pentiumii/manuals/245127.htm Intel ArchitectureSoftware Developer's Manuals IA-32 -
http://www.intel.com/design/pentium4/manuals/index_new.htm Intel Itanium 2 -
http://www.intel.com/design/itanium2/manuals/251110.htm Processor ReferenceManual for Software Development and Optimization -
ftp://download.intel.com/design/Itanium2/manuals/25111003.pdf

code optimize

requires: summery on all debug tools

cache size? 16K?