Linux系统中使用GCC CPU参数优化代码编译

Linux系统中使用GCC CPU参数优化代码编译

使用特定的GCC参数可以使编译出的程序执行效率有较大提升。具体如下:

1、优化原理:
在编译程序时,借助参数传递的方法,使用与系统CPU相匹配的gcc参数,编译出的程序就是为系统CPU而进行特定优化过的,因而执行速度和效率都会是最好。

2、注意事项
(1) 经过大量测试发现,在RedHat, CentOS系统中通常只能通过参数传递的方法进行编译优化,当然,如果愿意并且能够修改程序的MakeFile也可以达到这一效果,只不过比较复杂,工 作量较大。其他在网上广为流传的方法(例如:直接通过.bashrc, /etc/profile声明参数系统变量、写入/etc/make.conf等)经过测试均没有效果。

(2) 对于Gentoo Linux或FreeBSD可以通过修改/etc/make.conf添加参数的方法来实现,而不必使用参数传递法。

3、优化步骤:
(1)确定系统CPU类型:
# cat /proc/cpuinfo | grep "model name"
执行后会看到系统中CPU的具体型号,记下CPU型号。

(2)使用参数传递方法进行编译:(以Pentium4 CPU为例)
此处以编译Apache为例说明如何使用参数传递:
# tar xzvf httpd-2.0.55.tar.gz
# cd httpd-2.0.55
CHOST="i686-pc-linux-gnu" \
CFLAGS="-O3 \
-msse2 \
-mmmx \
-mfpmath=sse \
-mcpu=pentium4 \
-march=pentium4 \
-pipe \
-fomit-frame-pointer" \
CXXFLAGS="-O3 \
-msse2 \
-mmmx \
-mfpmath=sse \
-funroll-loops \
-mcpu=pentium4 \
-march=pentium4 \
-pipe \
-fomit-frame-pointer" \
./configure ......
# make
# make install

这样就通过函数传递方法实现了编译优化。下面对其中的一些参数进行具体说明:

-O3:相对于-O、-O1、-O2,-O3开启了所有GCC支持的优化特性;
-msse2:开启CPU所支持的sse2指令集;
-mmmx:参考-msse2
-mfpmath=sse:为指定指令集生成浮点运算特性(优化浮点运算功能);
-mcpu:指定CPU型号;
-march:指定CPU型号,基本同-mcpu,GCC根据-march设定的CPU型号决定在生成代码时可以使用哪些种类的指令。(注意!-march参数在某些CPU型号中不可用!)
-pipe:使用管道(pipe)方法替代临时文件方法在编译的不同阶段之间进行通讯。

附:常见CPU优化参数
386:
CHOST="i386-pc-linux-gnu"
CFLAGS="-march=i386 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=i386 -O3 -pipe -fomit-frame-pointer"
486:
CHOST="i486-pc-linux-gnu"
CFLAGS="-march=i486 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=i486 -O3 -pipe -fomit-frame-pointer"
Pentium (Intel):
CHOST="i586-pc-linux-gnu"
CFLAGS="-march=pentium -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium -O3 -pipe -fomit-frame-pointer"
Pentium MMX (Intel):
CHOST="i586-pc-linux-gnu"
CFLAGS="-march=pentium-mmx -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium-mmx -O3 -pipe -fomit-frame-pointer"
Pentium PRO (Intel):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentiumpro -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentiumpro -O3 -pipe -fomit-frame-pointer"
Pentium II (Intel):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium2 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium2 -O3 -pipe -fomit-frame-pointer"
Celeron (Intel):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium2 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium2 -O3 -pipe -fomit-frame-pointer"
Pentium III (Intel):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium3 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium3 -O3 -pipe -fomit-frame-pointer"
Celeron2 (Intel):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium3 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium3 -O3 -pipe -fomit-frame-pointer"
Celeron (Willamette-Intel):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium4 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium4 -O3 -pipe -fomit-frame-pointer"
Pentium 4 (Intel):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium4 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=pentium4 -O3 -pipe -fomit-frame-pointer"
K6 (AMD):
CHOST="i586-pc-linux-gnu"
CFLAGS="-march=k6 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=k6 -O3 -pipe -fomit-frame-pointer"
K6-2 (AMD):
CHOST="i586-pc-linux-gnu"
CFLAGS="-march=k6-2 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=k6-2 -O3 -pipe -fomit-frame-pointer"
K6-3 (AMD):
CHOST="i586-pc-linux-gnu"
CFLAGS="-march=k6-3 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=k6-3 -O3 -pipe -fomit-frame-pointer"
Athlon (AMD):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=athlon -O3 -pipe -fomit-frame-pointer"
Athlon-tbird, aka K7 (AMD):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-tbird -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=athlon-tbird -O3 -pipe -fomit-frame-pointer"
Athlon-tbird XP (AMD):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=athlon-xp -O3 -pipe -fomit-frame-pointer"
Athlon 4(AMD):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-4 -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=athlon-4 -O3 -pipe -fomit-frame-pointer"
Athlon XP (AMD):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=athlon-xp -O3 -pipe -fomit-frame-pointer"
Athlon MP (AMD):
CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-mp -O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-march=athlon-mp -O3 -pipe -fomit-frame-pointer"
603 (PowerPC):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
CXXFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
603e (PowerPC):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
CXXFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
604 (PowerPC):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
CXXFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
604e (PowerPC):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
CXXFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
750 aka as G3 (PowerPC):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=750 -O3 -pipe -fomit-frame-pointer -fsigned-char"
CXXFLAGS="-mcpu=750 -O3 -pipe -fomit-frame-pointer -fsigned-char"
7400, aka G4 (PowerPC):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=7400 -O3 -pipe -fomit-frame-pointer -fsigned-char -maltivec"
CXXFLAGS="-mcpu=7400 -O3 -pipe -fomit-frame-pointer -fsigned-char -maltivec"
7450, aka G4 second generation (PowerPC):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-mcpu=7450 -O3 -pipe -fomit-frame-pointer -fsigned-char -maltivec"
CXXFLAGS="-mcpu=7450 -O3 -pipe -fomit-frame-pointer -fsigned-char -maltivec"
PowerPC (If you don't know which one):
CHOST="powerpc-unknown-linux-gnu"
CFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
CXXFLAGS="-O3 -pipe -fomit-frame-pointer -fsigned-char"
Sparc:
CHOST="sparc-unknown-linux-gnu"
CFLAGS="-O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-O3 -pipe -fomit-frame-pointer"
Sparc 64:
CHOST="sparc64-unknown-linux-gnu"
CFLAGS="-O3 -pipe -fomit-frame-pointer"
CXXFLAGS="-O3 -pipe -fomit-frame-pointer"
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