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Drivers and the Kernel

Explore the roles of the kernel in a UNIX system, understand kernel-wide design approaches, learn to build custom kernels, and optimize FreeBSD performance through tuning. Step-by-step guide with references and troubleshooting tips.

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Drivers and the Kernel

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  1. Drivers and the Kernel

  2. Roles of the Kernel – (1) • Components of a UNIX System • User-level programs • Kernel • Hardware • Kernel manages the resources • CPU – process management • Memory – memory management • I/O devices – device management • Kernel provides method for • Inter-process communication (IPC) • Synchronization, communication • Processes to request resources • System calls

  3. Roles of the Kernel – (2)

  4. Kernel-wide Design Approaches • Monolithic kernels • Kernel space, shared memory, fast, …, need reboot • Eg. Linux, *BSD, MS-DOS, MS Windows 9x series… • Microkernels • User space, message passing, slow, …, as services • Eg. Mac OS X, BeOS, … • Hybrid • Monolithic + Micro • Eg. MS Windows NT series, DragonFly BSD, … • Nanokernels • Exokernels

  5. Why Build a Custom Kernel • FreeBSD kernel • Monolithic  modular • The functionality cannot be dynamically loadable • Building a custom kernel • To be an advanced BSD user • Time-consuming task • Customized kernel vs. GENERIC • Fast boot time • Lower memory usage • Additional hardware support • Fine-tune system performance • Such as adjusting important system parameters

  6. Finding the System Hardware • Before venturing into kernel configuration • Get an inventory of the machine’s hardware • Microsoft's Device Manager • dmesg • cat /var/run/dmesg.boot • pciconf -lv • man 4 ath • man -k Atheros psm0: <PS/2 Mouse> irq 12 on atkbdc0 psm0: [GIANT-LOCKED] psm0: [ITHREAD] psm0: model Generic PS/2 mouse, device ID 0 ath0@pci0:3:0:0: class=0x020000 card=0x058a1014 chip=0x1014168c vendor = 'Atheros Communications Inc.' device = 'AR5212 Atheros AR5212 802.11abg wireless' class = network subclass = ethernet

  7. Kernel Drivers and Modules • Before building a custom kernel • Load kernel modules to get the specific hardware support • Kernel modules • kldstat • kldload • /boot/kernel/*.ko • Modify /boot/loader.conf to load modules in boot time automatically • if_ath_load="YES" • kldunload zfs [/home/liuyh] -liuyh- kldstat Id Refs Address Size Name 1 62 0xffffffff80100000 6a2dc8 kernel 2 1 0xffffffff807a3000 1abd08 zfs.ko 3 2 0xffffffff8094f000 3a68 opensolaris.ko 4 4 0xffffffff80953000 1f348 krpc.ko 5 1 0xffffffff80973000 bc28 geom_label.ko

  8. Building and Installing a Custom Kernel – (1) • Obtain full FreeBSD source tree • sysinstall • Configure  Distributions  src  All • csup • csup -h cvsup.tw.freebsd.org /usr/share/examples/cvsup/standard-supfile • Customized kernel configuration file • Sample files • /usr/src/sys/<ARCH>/conf • GENERIC, NOTES, LINT (generated by “make LINT”) • /usr/src/sys/conf/NOTES for architecture independent options • Customized file • cp GENERIC /usr/local/etc/MYKERNEL • ln -s /usr/local/etc/MYKERNEL /usr/src/sys/<ARCH>/conf/

  9. Building and Installing a Custom Kernel – (2) • Building a kernel • cd /usr/src • make buildkernel KERNCONF=MYKERNEL • make installkernel KERNCONF=MYKERNEL • kernel = buildkernel + installkernel • MODULES_OVERRIDE • Set to a list of modules to build instead of all of them • NO_MODULES • Set to not build modules with the kernel • WITHOUT_MODULES • Set to a list of modules to exclude from the build • Kernel locations • /boot/kernel/kernel • /boot/kernel  /boot/kernel.old make.conf(5)

  10. The Configuration File • Each line contains a keyword and one or more arguments • http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig-config.html

  11. If Something Goes Wrong • Config failed • Make sure the keyword is typed correctly • Make failed • Look over your configuration • Send mail to the FreeBSD general questions mailing list with kernel configuration • Boot failed • ok mode • boot kernel.old • unload kernel && load /boot/kernel.old/kernel && boot • nextboot(8) • ps(1) failed • Recompile and install a world

  12. Ok mode

  13. Tuning the FreeBSD Kernel • sysctl command • Dynamically set or get kernel parameters • All changes made by sysctl will be lost across reboot • Use sysctl to tune the kernel and test it, then recompile the kernel • Format: % sysctl [options] name[=value] … Ex: % sysctl –a list all kernel variables % sysctl –d kern.maxfiles print the description of the variable % sysctl kern.maxfiles print the value of the variable % sudo sysctl kern.maxfiles=2048

  14. Reference • References • http://www.freebsd.org/doc/en/books/handbook/kernelconfig-config.html • /usr/src/sys/<ARCH>/conf • NOTES • LINT • GENERIC • Further reading • http://www.freebsd.org/doc/handbook/configtuning-kernel-limits.html • http://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug.html

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