542 lines
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542 lines
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>Securing and Optimizing Linux: RedHat Edition -A Hands on Guide</TH
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>Prev</A
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>Chapter 6. Linux General Optimization</TD
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WIDTH="10%"
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ALIGN="right"
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>Next</A
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="section"
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><H1
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CLASS="section"
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><A
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NAME="AEN4340"
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>6.1. The /etc/profile file</A
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></H1
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><P
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> The <TT
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CLASS="filename"
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>/etc/profile</TT
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> file contains system wide environment stuff and startup programs. All customizations that you put in this file will apply for the entire environment variable on your system, so putting optimization
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flags in this file is a good choice. To squeeze the most performance from your x86 programs, you can use full optimization when compiling with the <TT
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CLASS="literal"
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>-O9</TT
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> flag. Many programs contain <TT
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CLASS="literal"
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>-O2</TT
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> in
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the Makefile. <TT
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CLASS="literal"
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>-O9</TT
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> is the highest level of optimization. It will increase the size of what it produces, but it runs faster.
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</P
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><P
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> Please Note it is not always true that the <TT
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CLASS="literal"
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>-O9</TT
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> flag will make the best performance for your processor. If you have an x686 and above processor, surely, but below x686, not necessarily.
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</P
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><P
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> When compiling, use the <TT
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CLASS="envar"
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>-fomit-frame-pointer</TT
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> switch for any kind of processor you may have. This will use the stack for accessing variables. Unfortunately, debugging is almost impossible with this option. You can also use
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the <TT
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CLASS="envar"
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>-mcpu=cpu_type</TT
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> and <TT
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CLASS="envar"
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>-march=cpu_type</TT
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> switch to optimize the program for the <SPAN
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CLASS="acronym"
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>CPU</SPAN
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> listed to the best of <SPAN
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CLASS="acronym"
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>GCC's</SPAN
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> ability. However, the resulting code will only be run able on
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the indicated <SPAN
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CLASS="acronym"
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>CPU</SPAN
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> or higher.
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</P
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><P
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> The optimization options apply only when we compile and install a new program in our server. These
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optimizations don't play any role in our Linux base system; it just tells our compiler to optimize the new programs that we will install with the optimization flags we have specified in the <TT
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CLASS="filename"
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>/etc/profile</TT
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> file.
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</P
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><P
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> Below are the optimization flags that we recommend you put in your <TT
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CLASS="filename"
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>/etc/profile</TT
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> file depending on your <SPAN
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CLASS="acronym"
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>CPU</SPAN
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> architecture.
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</P
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><DIV
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CLASS="procedure"
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><P
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><B
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>Recommended optimization flags</B
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></P
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><OL
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TYPE="1"
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><LI
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><P
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> For <SPAN
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CLASS="acronym"
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>CPU</SPAN
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> i686 or <SPAN
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CLASS="hardware"
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>PentiumPro, Pentium II, Pentium III</SPAN
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>
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In the <TT
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CLASS="filename"
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>/etc/profile</TT
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> file, put this line for a PentiumPro, Pentium II and III Pro Processor family:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="screen"
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> <TT
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CLASS="envar"
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>CFLAGS=-O9 -funroll-loops -ffast-math -malign-double -mcpu=pentiumpro -march=pentiumpro -fomit-frame-pointer -fno-exceptions</TT
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>
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</PRE
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></TD
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></TR
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></TABLE
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>
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</P
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><P
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> For <SPAN
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CLASS="acronym"
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>CPU</SPAN
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> <SPAN
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CLASS="hardware"
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>i586</SPAN
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> or Pentium:
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In the <TT
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CLASS="filename"
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>/etc/profile</TT
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> file, put this line for a Pentium Processor family:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="screen"
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> <TT
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CLASS="envar"
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>CFLAGS=-O3 -march=pentium -mcpu=pentium -ffast-math -funroll-loops -fomit-frame-pointer -fforce-mem -fforce-addr -malign-double -fno-exceptions</TT
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>
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</PRE
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></TD
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></TR
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></TABLE
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>
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</P
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><P
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> For <SPAN
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CLASS="acronym"
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>CPU</SPAN
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> <SPAN
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CLASS="hardware"
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>i486</SPAN
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>:
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In the <TT
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CLASS="filename"
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>/etc/profile</TT
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> file, put this line for a <SPAN
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CLASS="hardware"
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>i486</SPAN
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> Processor family:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="screen"
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> <TT
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CLASS="envar"
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>CFLAGS=-O3 -funroll-all-loops -malign-double -mcpu=i486 -march=i486 -fomit-frame-pointer -fno-exceptions</TT
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>
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</PRE
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></TD
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></TR
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></TABLE
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>
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</P
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></LI
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><LI
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><P
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> Now after the selection of your <SPAN
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CLASS="acronym"
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><SPAN
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CLASS="acronym"
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>CPU</SPAN
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></SPAN
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> settings <SPAN
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CLASS="hardware"
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>-i686, i586, or i486</SPAN
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> a bit further down in the <TT
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CLASS="filename"
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>/etc/profile</TT
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> file,
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add <TT
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CLASS="envar"
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>CFLAGS LANG LESSCHARSET</TT
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> to the export line:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="screen"
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> <B
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CLASS="command"
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>export</B
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> <TT
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CLASS="envar"
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>PATH PS1 HOSTNAME HISTSIZE HISTFILESIZE USER LOGNAME MAIL INPUTRC CFLAGS LANG LESSCHARSET</TT
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>
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</PRE
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></TD
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></TR
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></TABLE
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>
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</P
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></LI
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><LI
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><P
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> Log out and log back in; after this, the new <TT
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CLASS="envar"
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>CFLAGS</TT
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> environment variable is set, and software and other configure tool will recognize that.
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Pentium Pro/II/III optimizations will only work with egcs or pgcc compilers. The egcs compiler is already installed on your Server by default
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so you don't need to worry about it.
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</P
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></LI
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></OL
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></DIV
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><P
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> Below is the explanation of the different optimization options we use:
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<DIV
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CLASS="glosslist"
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><DL
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><DT
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><B
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> <TT
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CLASS="envar"
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>-funroll-loops</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-funroll-loops</TT
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> optimization option will perform the optimization of loop unrolling and will do it only for loops whose number of iterations can be
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determined at compile time or run time.
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</P
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></DD
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><DT
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><B
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><TT
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CLASS="envar"
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>-funroll-all-loops</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-funroll-all-loops</TT
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> optimization option will also perform the optimization of loop unrolling and is done for all loops.
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</P
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></DD
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><DT
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><B
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><TT
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CLASS="envar"
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>-ffast-math</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-ffast-math</TT
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> optimization option will allow the GCC compiler, in the interest of optimizing code for speed, to violate
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some <SPAN
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CLASS="acronym"
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>ANSI</SPAN
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> or <SPAN
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CLASS="acronym"
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>IEEE</SPAN
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> rules/specifications.
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</P
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></DD
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><DT
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><B
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><TT
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CLASS="envar"
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>-malign-double</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-malign-double</TT
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> optimization option will control whether the <SPAN
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CLASS="acronym"
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>GCC</SPAN
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> compiler aligns double, long double, and long long variables on a two-word boundary or a one-word
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boundary. This will produce code that runs somewhat faster on a Pentium at the expense of more memory.
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</P
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></DD
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><DT
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><B
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><TT
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CLASS="envar"
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>-mcpu=cpu_type</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-mcpu=cpu_type</TT
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> optimization option will set the default <SPAN
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CLASS="acronym"
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><SPAN
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CLASS="acronym"
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>CPU</SPAN
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></SPAN
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> to use for the machine type when scheduling instructions.
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</P
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></DD
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><DT
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><B
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><TT
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CLASS="envar"
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>-fforce-mem</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-fforce-mem</TT
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> optimization option will produce better code by forcing memory operands to be copied into registers before doing arithmetic on them and by making
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all memory references potential common subexpressions.
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</P
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></DD
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><DT
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><B
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><TT
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CLASS="envar"
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>-fforce-addr</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-fforce-addr</TT
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> optimization option will produce better code by forcing memory address constants to be copied into registers before doing arithmetic on them.
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</P
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></DD
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><DT
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><B
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><TT
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CLASS="envar"
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>-fomit-frame-pointer</TT
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>
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</B
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></DT
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><DD
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><P
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> The <TT
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CLASS="envar"
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>-fomit-frame-pointer</TT
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> optimization option, one of the most interesting, will allow the program to not keep the frame pointer in a register for functions that don't need one. This
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avoids the instructions to save, set up and restores frame pointers; it also makes an extra register available in many functions and makes debugging impossible on most machines.
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</P
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></DD
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></DL
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></DIV
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>
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</P
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><DIV
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CLASS="important"
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><BLOCKQUOTE
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CLASS="important"
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><P
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><B
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><SPAN
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CLASS="inlinemediaobject"
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><IMG
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SRC="./images/Important.gif"
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ALT="Important"
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></IMG
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></SPAN
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>: </B
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>
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All future optimizations that we will describe in this book refer by default to a Pentium II/III <SPAN
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CLASS="acronym"
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>CPU</SPAN
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> family. So you must, if required, adjust the compilation flags for your specific <SPAN
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CLASS="acronym"
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><SPAN
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CLASS="acronym"
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>CPU</SPAN
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></SPAN
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> processor type in
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the <TT
|
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CLASS="filename"
|
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>/etc/profile</TT
|
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> file and also during your compilation time.
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</P
|
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></BLOCKQUOTE
|
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></DIV
|
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|
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>Prev</A
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ALIGN="center"
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>Home</A
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HREF="chap6sec65.html"
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>Next</A
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>Linux General Optimization</TD
|
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="gen-optim.html"
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>Up</A
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></TD
|
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Benchmark Results</TD
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></TR
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