Linux Tutorial: System Enhancements, Optimization and ...



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System Enhancements, Optimization and Compiling the Kernel

|Tutorial Index: |[|

|# Optimize hard drive access performance |p|

|# Kernel Tweaks |i|

|# Compiling the Kernel |c|

|# Kernel Source and Patches |]|

|# Tips | |

|# Info | |

|# Books | |

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This tutorial covers optimization techniques to make your system run faster or support your needs better. This may include tweaking configuration specifications, turning off un-needed processes, and compiling a new kernel tweaked for your system. Note that graphics device drivers are NOT compiled into the kernel although support for interfacing with their particular chipset can be compiled in. This is because X-Windows is an application running on Linux and not integral to the kernel.

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|[p|Optimize hard drive access performance: |

|ic| |

|] |Hdparm: |

|[p|The following optimizations techniques can be applied to (E)IDE drives to utilize 32 bit I/O and DMA more effectively. |

|ic|Get info: hdparm /dev/hda |

|][|Get more info: hdparm -I /dev/hda |

|pi|Test Speed: hdparm -tT /dev/hda |

|c]|Increase Speed: hdparm -d1 -c3 -u1 /dev/hda |

| |-d1: Turn on DMA (0: off) |

| |-c3: IDE chipset support |

| |0: Disable |

| |1: Enable |

| |3: 32 bit transfer |

| |-u1: Get/set interrupt umask. Driver ignores other interrupts during processing of disk interrupts. (0: off) |

| |Test Speed Again: hdparm -tT /dev/hda |

| |The Red Hat 7.1+/8.0 configuration uses /etc/rc.sysinit to call scripts /etc/sysconfig/harddisks. (Earlier systems used: |

| |/etc/sysconfig/harddiskhda, /etc/sysconfig/harddiskhdb, etc) to run hdparm upon boot. |

| |File: /etc/sysconfig/harddisks: |

| |USE_DMA=1 |

| |EIDE_32BIT=1 |

| |Turn off hdparm DMA access: hdparm -d0 /dev/hda |

| |Links: |

| |hdparm man page. |

| |Optimizing hard drive performance with hdparm. |

| |ATA, UDMA and hdparm |

| |[pic] |

| |Ramdisk: |

| |Go even faster by using ramdisk - Memory mapped as a disk. See: How to use a Ramdisk for Linux |

| |Also see: /usr/src/linux-2.4/Documentation/ramdisk.txt |

| |Tools: |

| |Measure hared drive performance with IBM Drive Fitness Test (DFT) utility. Create a boot floppy with DFT image (use dd) and |

| |boot. Measures SCSI and IDE performance as well as some repair utilities. |

| |IoMeter: Server I/O benchmark tool. |

| |[pic] |

| |Kernel Tweaks: |

| | |

| |Direct kernel to specify processor affinity for a process: |

| |Set (or retrieve) the CPU affinity. The scheduler attempts to keep the process on the specified CPU. This is especially |

| |effective for threaded applications to improve cache coherancy on SMP computers. It is also usefull for software licensed to a |

| |CPU or for a single CPU system when it is in fact running on an SMP system. (i.e. Oracle) |

| |taskset: retrieve or set a processes's CPU affinity |

| |(Part of package "schedutils") |

| |sched_setaffinity / sched_getaffinity: set and get a process's CPU affinity mask |

| |Kernel enhancements to optimize SCSI for scanner access: |

| |See man page for sane: man sane-scsi |

| |Excerp from man page: |

| |First, make sure your kernel has SCSI generic support |

| |enabled. In ``make xconfig'', this shows up under ``SCSI |

| |support->SCSI generic support''. |

| | |

| |To keep scanning times to a minimum, it is strongly recom� |

| |mended to use a large buffer size for the generic SCSI |

| |driver. By default, Linux uses a buffer of size 32KB. |

| |This works, but for many cheaper scanners this causes |

| |scanning to be slower by about a factor of four than when |

| |using a size of 127KB. Linux defines the size of this |

| |buffer by macro SG_BIG_BUFF in header file |

| |/usr/include/scsi/sg.h. Unless a system is seriously |

| |short on memory, it is recommended to increase this value |

| |to the maximum legal value of 128*1024-512=130560 bytes. |

| |After changing this value, it is necessary to recompile |

| |both the kernel (or the SCSI generic module) and the SCSI |

| |backends. |

| | |

| |AUTHOR |

| |David Mosberger 13 May 1998 |

| | |

| | |

| | |

| |Kernel enhancements to increase the per process limit of open files: |

| |Change the definition of NR_OPEN in local files: |

| |/usr/src/linux/include/linux/limits.h (Local file: kernel 2.2 RH 7.0-) (default 1024 typ.) |

| |/usr/include/limits.h (Local file) (default 1024 typ.) |

| |/usr/src/linux/include/linux/fs.h (Local file: kernel 2.2 RH 7.0-) |

| |[pic] |

| |Compiling the Kernel: |

| | |

| |The default Red Hat Kernel comes with as much stuff compiled into the Kernel as they could fit. This allows it to support a vast|

| |array of devices and system needs. If you must add support for something new or if you wish to streamline your kernel with only |

| |what is needed so that it uses less memory, operates faster, and is optimized for your processor, then one must recompile the |

| |kernel. |

| |To find out about the latest kernel, issue the command: finger @finger. |

| |Typically the source code for the Red Hat installation is located in: |

| |/usr/src/redhat/SOURCES/ - patches and kernel will be placed here by kernel source RPM. (Fedora Core 3) |

| |(bzip2 -d linux-2.6.9.tar.bz2, tar xf linux-2.6.9.tar) |

| |/usr/src/linux/ - (Soft linked to /usr/src/linux-2.2.xx) Kernel 2.2 and older. (Red Hat 6.x, 7.0) |

| |/usr/src/linux-2.4/ - (Soft linked to /usr/src/linux-2.4.xx) Kernel 2.4. (Red Hat 7.1) |

| |This separation to a new directory for kernel 2.4 is to accommodate the differences between the C library and the kernel. |

| |If you get new kernel source download to a new directory. i.e. /usr/src/linux-2.2.16 then ln -s /usr/src/linux-2.2.16 |

| |/usr/src/linux |

| |Typically the kernel RPM (kernel-source-XXX.i386.rpm) will install the source and generate the appropriate links. |

| |Perform the following steps: (as root) |

| |Setup: |

| |The source may already be installed as part of the installation or from an RPM (See /usr/src/). |

| |OR |

| |You may also download the latest source from . |

| |Move the downloaded file linux-2.X.XX.tar.gz to /usr/src/. |

| |Uncompress file: tar -xzf linux-2.X.XX.tar.gz which will install everything in a subdirectory linux/. (To view contents use |

| |command tar -tzf linux-...tar.gz) |

| |If using the file with the bz2 extension: bunzip2 linux-2.X.XX.tar.bz2 |

| |cd /usr/src/linux/ (or /usr/src/linux-2.4/) |

| |less README (Read the documentation. It tells you everything. Use space bar to view next page) |

| |(Local links to: /usr/src/linux/README or /usr/src/linux-2.4/README) |

| |Update /usr/include/ |

| |NOTE: PERFORM THIS STEP FOR KERNEL 2.2.x AND OLDER. DO NOT DO THIS FOR KERNEL 2.4. |

| |The header files for Kernel 2.4 and the C library header files may no longer match and thus must remain separated. |

| |cd /usr/include |

| |rm -fr asm linux scsi |

| |ln -s /usr/src/linux/include/asm asm |

| |ln -s /usr/src/linux/include/linux linux |

| |ln -s /usr/src/linux/include/scsi scsi |

| |The soft links (ln -s) to the include directories are important to software developers who need to compile with the new include |

| |files. |

| |Note: The sym link is optional and some don't do it due to potential differences in the header files used by glibc and the |

| |kernel. (A response from Linus) |

| |cd /usr/src/linux (or /usr/src/linux-2.4) |

| |make distclean (Cleans up junk from old compiles) (Warning: removes .config) |

| |make mrproper (build the source tree) |

| |At this time the sources are correctly installed. This also resets the /usr/src/linux/.config file to the system default. |

| |SuSE setup: |

| |For SuSE (9.3), there are two kernel-source RPMs. One RPM resides on the "Source" DVD-2 and the other resides on the |

| |"Installation" DVD-1. Use the kernel-source RPM found on the "Installation" DVD-1. This one will register in the RPM database |

| |and creates the directories expected |

| |Check with the command: rpm -q kernel-source |

| |Kernel source code location: /usr/src/linux |

| |Docs location: /usr/share/doc/packages/kernel-source |

| |The SuSE kernel-source RPM will not produce a ".config" file for the kernel compilation. |

| |Produce the default ".config" file by: zcat /proc/config.gz > /usr/src/linux/.config |

| |Configuration: |

| |Use one of the following tools to create the .config file. This gives you the chance to choose what goes into the kernel. You |

| |can choose support for many of the latest capabilities, device drivers, and can tune the kernel for particular uses. i.e. you |

| |can also optimize the compilation for the Pentium. (Default for RH 5.2 was a 386 with no math co-processor!) The default config |

| |file used to compile the default distribution kernel can be found in the source directory. (i.e. Fedora Core 3: |

| |/usr/src/redhat/SOURCES/kernel-2.6.9-i686.config, /usr/src/redhat/SOURCES/kernel-2.6.9-x86_64-smp.config, ... and all the others|

| |for the various hardware platforms.) |

| |Pick one of the following: |

| |make config (Bash shell script) |

| |make menuconfig (uses text window curses) |

| |make xconfig (uses tck and wish) - recommended due to online help feature and intuitive interface. Save configuration to file: |

| |.config |

| |make oldconfig Build a configuration file based on defaults found in current .config file. |

| |menuconfig Notes: "< > options can be compiled as a module. |

| | = Compile into kernel (y) |

| | = Compile as a module (m) |

| |Recommendation for Pentium owners: General Setup choose : |

| |Kernel math emulations: N |

| |Processor type: Pentium |

| |Development, experimental or kernel debugging features: N |

| |If using netfilter capabilities, do not enable the kernel fast-switching option. That code will permits fast switching at a |

| |lower level in the IP stack than netfilter and thus will bypass the netfilter capabilities. |

| |Note: When requiring gobs of memory (> 1Gb), there is a kernel compile option which sets the limit on the amount of user memory |

| |one can use: "Processor type and features / Maximum Virtual Memory". |

| |Compile: |

| |Next: (from /usr/src/linux) |

| |make dep (make dependencies. Older kernels only. Attempt and if not needed, make will return a message stating that this step is|

| |un-necessary. Not required for 2.6+ kernels.) |

| |make clean (At this point you have all the source gathered) |

| |Choose one of the following to create the new kernel and then move it to /boot/vmlinux: |

| |make zImage (compressed image) |

| |make bzImage (very compressed image good for recovery floppies - slower to boot because of time to uncompress) |

| |make image |

| |make bzdisk (Boot floppy with no LILO) |

| |Install: |

| |mv /usr/src/linux/arch/i386/boot/zImage /boot/vmlinuz-release |

| |ln -s /boot/vmlinuz-release /boot/vmlinuz |

| |(If "make zImage" was chosen) |

| |or |

| |mv /usr/src/linux/arch/i386/boot/bzImage /boot/vmlinuz-release |

| |ln -s /boot/bzImage-release /boot/vmlinuz |

| |(If "make bzImage" was chosen) |

| |Also move/copy the file /usr/src/linux.../System.map to /boot/System.map-2.X.XX |

| |OR |

| |make install |

| |(Preferred. Potential Pitfall: On my SCSI system I had to execute this command after issuing the mkinitrd command below.) |

| |Modules documentation: (not that helpful) |

| |/usr/src/linux-2.4/Documentation/modules.txt |

| |/usr/src/linux/Documentation/modules.txt |

| |make modules |

| |rm /lib/modules/Kernel_release (i.e. /lib/modules/2.2.16-3 ) |

| |ln -s /lib/modules/new_modules_directory /lib/modules/Kernel_release |

| |make modules_install |

| |Generates the file: /lib/modules/2.X.XX/modules.dep |

| |Configure Boot Loader: |

| |(Grub or Lilo) |

| |Configure grub: |

| |File: /etc/grub.conf |

| |default=1 - Kernel to boot (2nd in list) |

| |timeout=5 |

| |splashimage=(hd1,0)/boot/grub/splash.xpm.gz - Boot image location (hd1, 1st partition) |

| |hiddenmenu |

| |title Fedora Core (2.6.12-1.1372_FC3) |

| |root (hd1,0) - Root of GRUB reference. Same as /boot |

| |kernel /boot/vmlinuz-2.6.12-1.1372_FC3 ro root=LABEL=/ rhgb quiet |

| |initrd /boot/initrd-2.6.12-1.1372_FC3.img |

| |title Fedora Core (2.6.11-1.14_FC3) |

| |root (hd1,0) |

| |kernel /boot/vmlinuz-2.6.11-1.14_FC3 ro root=LABEL=/ rhgb quiet |

| |initrd /boot/initrd-2.6.11-1.14_FC3.img |

| | |

| | |

| |Description: |

| |default: Default kernel to boot. All options displayed but one will boot by default. |

| |timeout: Time for user to select kernel. After "timeout" seconds, default kernel chosen and boot begins. |

| |splashimage: Background image shown by Grub and location (hard drive hd1 and "0" or first partition (/boot). |

| |root: Grub root directory. In this example, drive hd1 and "0" or first partition (/boot). |

| |kernel: Kernel to boot, read only. Note that this is the same as the result of cat /proc/cmdline |

| |initrd: Initial ramdisk for a Linux format boot image. Sets parameters in the Linux setup area in memory. |

| |See: |

| |Grub Home page |

| |grub shell man page. |

| |Configure lilo: Lilo must point to the new kernel. Edit /etc/lilo.conf. Add a new image statement to point to the new kernel. |

| |Keep the old as backup in case you need to boot it. |

| |SCSI systems must perform an additional step to load drivers upon system boot: |

| |Execute the following command which creates the file used to let the system boot: |

| |mkinitrd /boot/initrd-2.2.16-3.img 2.2.16-3 |

| |The second argument is the name of the sub-directory of the modules under the directory /lib/modules/. (In this case |

| |/lib/modules/2.2.16-3/ |

| |This step is required by systems using modular SCSI support. If the SCSI support is compiled into the kernel and is NOT a |

| |module, then this step may not be necessary. The file /boot/initrd-2.2.16-3.img is specified as the RAM disk image used before |

| |the file system is available. (initrd = initial ram disk) |

| |Run /sbin/lilo -v to configure the master boot record with data from lilo.conf. |

| |Sample lilo.conf: |

| |boot=/dev/sda |

| |map=/boot/map - Location of the kernel used for boot |

| |install=/boot/boot.b |

| |prompt |

| |timeout=50 |

| |linear - Specific to SCSI configurations |

| |default=linux |

| | |

| |image=/boot/vmlinuz-2.2.16-3 - New kernel |

| |label=linux - Name to be displayed by Lilo boot manager |

| |initrd=/boot/initrd-2.2.16-3.img - Specific to SCSI boot drives. |

| |read-only |

| |root=/dev/sdb6 |

| | |

| |image=/boot/vmlinuz-2.2.14-5.0 |

| |label=OldLinux |

| |initrd=/boot/initrd-2.2.14-5.0.img - SCSI specific. |

| |read-only |

| |root=/dev/sdb6 |

| | |

| | |

| |When the system boots and gives you the "Lilo:" prompt, you can type "?" to see your boot choices as defined by the above labels|

| |in lilo.conf. Type the label name of the kernel or system you wish to boot. A carriage return will choose the default. |

| |For a full list of boot parameters see: bootparam man page |

| |Also see the Boot Prompt Howto. |

| |Kernel version verification: uname -rv will print the compile date of the kernel currently running. |

| |[pic] |

| |Modules: |

| |Modules are used to reduce the amount of memory used to hold the kernel. There is a slight penalty for the time taken to load |

| |and unload the module. |

| |If the code is required for general operation of the kernel or is needed often or required by the boot process, it is best to |

| |compile it into the kernel and it should NOT be compiled as a module. |

| |Module commands: |

| |The kernel will use the modprobe utility to determine if the module is compatible with the kernel. |

| |The program used is specified by a proc file: |

| |cat /proc/sys/kernel/modprobe |

| |/sbin/modprobe - Result of cat operation |

| |Modules are loaded by init scripts which call insmod/rmmod to load/unload modules. |

| |Command |

| |Description |

| | |

| |lsmod |

| |List loaded modules |

| |[pic] |

| |[ /root]# lsmod |

| |Module Size Used by |

| |3c59x 19716 0 (autoclean) (unused) |

| |autofs 9120 1 (autoclean) |

| |emu10k1 45688 1 |

| |soundcore 2596 4 [emu10k1] |

| |aic7xxx 137400 3 |

| | |

| |insmod |

| |Inserts a module into the active kernel |

| | |

| |rmmod |

| |Remove a loaded module. Just specify the module name. No ".o" or path necessary. |

| | |

| |modprobe |

| |High level handling of loadable modules. |

| |Loads module and dependencies. |

| | |

| |depmod |

| |Creates dependencies file for a module (used by modprobe) |

| | |

| |modinfo |

| |Display information about a kernel module |

| | |

| |List of modules held in /etc/modules.conf (or for older systems: /etc/conf.modules) |

| |Sample: |

| |alias scsi_hostadapter aic7xxx |

| |alias eth0 eepro100 |

| |alias eth1 eepro100 |

| |alias parport_lowlevel parport_pc |

| |alias sound-slot-0 emu10k1 |

| |alias char-major-81 bttv |

| | |

| |Other useful commands: |

| |Display system status gathered from /proc: /usr/bin/procinfo -a |

| |List Processor type: cat /proc/cpuinfo |

| |List devices: |

| |cat /proc/devices |

| |/sbin/lsmod |

| |List IO ports (devivce address used drivers): cat /proc/ioports |

| |List DMA channels: cat /proc/dma |

| |View interrupts used by the system: |

| |cat /proc/interrupts |

| |procinfo -i |

| |IRQ |

| |Description |

| | |

| |0 |

| |Timer channel 0 |

| | |

| |1 |

| |Keyboard |

| | |

| |2 |

| |Cascade for controller 2 (which controls IRQ 8-15) |

| | |

| |3 |

| |Serial Port 2 (COM2) |

| | |

| |4 |

| |Serial Port 1 (COM1) |

| | |

| |5 |

| |Parallel Port 2 (LPT2) |

| | |

| |6 |

| |Floppy Diskette Controller |

| | |

| |7 |

| |Parallel Port 1 (Printer LPT1) |

| | |

| |8 |

| |Real-time Clock |

| | |

| |9 |

| |Redirected to IRQ2 |

| | |

| |10 |

| |-- |

| | |

| |11 |

| |-- |

| | |

| |12 |

| |PS/2 Mouse |

| | |

| |13 |

| |Math Co-processor |

| | |

| |14 |

| |Hard Disk Controller (IDE) |

| | |

| |15 |

| |-- |

| | |

| | |

| |Also see file: |

| |/etc/isapnp.gone for a list of protected IRQ's which will not be allocated to ISA Plug and Play device. |

| |Command: pnpdump |

| |This command scans ISA PnP cards and can be used to generate /etc/isapnp.conf |

| |pnpdump > /etc/isapnp.conf |

| |Command: isapnp -C /etc/isapnp.conf |

| |Uses file /etc/isapnp.gone and /proc files to avoid IRQ's already allocated and to determine safe IRQ's. |

| |Home page for "isapnptools" |

| |Plug and Play ISA Specification |

| |Create devices. Run script: /dev/MAKEDEV |

| |Display kernel version in current use: /proc/version |

| |Display boot messages: dmesg |

| |Display sound driver status: cat /dev/sndstat |

| |[pic] |

| |Kernel Source and Patches: |

| | |

| |Linux kernel naming convention: Version.MajorRelease.MinorRelease.PatchNumber |

| |(In Linux kernel vernacular: KernelVersion.PatchLevel.Sublevel.Extraversion) |

| |Patch File Description: The patch files are file "diffs" (differences from the stated source file) which can be applied to |

| |create a newer updated file. |

| |Downloading kernel source and applying a patch: |

| |Obtain kernel source: |

| |Uncompress: tar xzf linux-2.X.X.tar.gz |

| |(Or: tar xjf linux-2.X.X.tar.bz2) |

| |This creates the local directory: linux/... |

| |OR |

| |use the source from the kernel-source RPM package released by your distribution. Using the source released by your distribution |

| |will include patches and source code needed to support all the features of your distribution. Of greatest importance is the |

| |default ".config" file which describes the features used by your distribution. i.e. Red Hat / Fedora Core use the ext3 file |

| |system, devfs and turn on many features by default. |

| |Download patch: |

| |Download patch: |

| |(Place patches in directory (create it first): /usr/src/KernelPatches/) |

| |Apply patch: Apply patches from default source directory /usr/src/linux (linked to actual source directory): |

| |gzip -cd ../KernelPatches/patch-file.gz | patch -p0 |

| |bzip2 -dc ../KernelPatches/patch-file.bz2 | patch -p0 |

| |If patch file resides in directory /usr/src/linux: |

| |zcat patch-file.gz | patch -p0 |

| |Use script patch-kernel if applying multiple patches at once: (i.e. patch-2.6.11.5 to patch-2.6.11.7) |

| |(Script located in directory linked to kernel source) |

| |Place all patches in /usr/src/KernelPatches/ (.gz or .bz2) |

| |Apply all the patches to kernel (i.e. 2.6.11.4) |

| |/usr/src/linux/scripts/patch-kernel linux KernelPatches |

| |(Execute from directory /usr/src) |

| |Or apply all the patches to kernel to bring it up to specified level. |

| |/usr/src/linux/scripts/patch-kernel linux KernelPatches 2.6.11.7 |

| |(patch-kernel kernel-source-directory-to-act-on highest-version to include) |

| |Set-up directory links: |

| |mv linux linux-2.X.XX (only required on some older RPMs) |

| |ln -s linux-2.X.XX linux |

| |/usr/include/asm should point to /usr/src/linux/include/asm-i386 |

| |/usr/include/linux should point to /usr/src/linux/include/linux |

| |/usr/include/scsi should point to /usr/src/linux/include/scsi |

| |[pic] |

| |Example: Applying the devfs patch to kernel 2.2.20 |

| |Download kernel: |

| |mv linux-2.2.20.tar.gz /usr/src |

| |cd /usr/src/ |

| |Remove previous source: rm linux (May use rm -Rf linux/) |

| |Unload to subdirectory linux/: tar xzf linux-2.2.20.tar.gz |

| |Download patch: |

| |Download patch file devfs-patch-current to /usr/src/ |

| |cd /usr/src |

| |Test: patch -p0 --dry-run < devfs-patch-current |

| |Apply patch: patch -p0 < devfs-patch-current |

| |Now go through regular kernel build as described above. (From the beginning) make distclean; make mrproper |

| |The configuration has been altered by the patch thus make xconfig will have options not seen in the original 2.2.20 kernel. |

| |"Code maturity level" option |

| |Select "development and/or incomplete code/drivers" |

| |This will provide lots of options for kernel. |

| |Go to Filesystems - check /dev file support "Experimental" |

| |This feature was introduced by the patch. If it is not selected the devfs feature introduced by the patch will not be included. |

| |Kernel source must be in /usr/src/linux/ (From ) or /usr/src/linux-2.2.20/ for the patch command as given, to work. |

| |The patch is pre-configured for this. |

| |Patch command options: |

| |Option |

| |Description |

| | |

| |-DMACRO-NAME |

| |Define pre-processor macro |

| | |

| |-c |

| |Use diff file format. |

| | |

| |-d directory |

| |Change to directory. |

| | |

| |--dry-run |

| |Don't modify file but output results. |

| | |

| |-s |

| |Silent mode. |

| | |

| |-f |

| |Force change. |

| | |

| |-n |

| |Using patch file which is a regular diff file. |

| | |

| |-R |

| |Reverse or undo patch. (i.e. if patch rejected.) |

| | |

| |-p0 |

| |Do not strip directory path prefix. Path intact. i.e. /usr/src/linux/... |

| | |

| |-p1 |

| |Strip first "/" in directory path. i.e. usr/src/linux/... |

| | |

| |-p2 |

| |Strip first directory in path. i.e. src/linux/... |

| | |

| |-p# |

| |Directory path "/" prefixes to strip (# - 1). |

| | |

| |Look at the patch file to see the directory path you will reference. |

| |View patch file: zcat patch-file.gz | more |

| |patch man page. |

| |[pic] |

| |[pic] |

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