FreeBSD src
407cb1012e
enabled in critical sections and streamline critical_enter() and critical_exit(). This commit allows an architecture to leave interrupts enabled inside critical sections if it so wishes. Architectures that do not wish to do this are not effected by this change. This commit implements the feature for the I386 architecture and provides a sysctl, debug.critical_mode, which defaults to 1 (use the feature). For now you can turn the sysctl on and off at any time in order to test the architectural changes or track down bugs. This commit is just the first stage. Some areas of the code, specifically the MACHINE_CRITICAL_ENTER #ifdef'd code, is strictly temporary and will be cleaned up in the STAGE-2 commit when the critical_*() functions are moved entirely into MD files. The following changes have been made: * critical_enter() and critical_exit() for I386 now simply increment and decrement curthread->td_critnest. They no longer disable hard interrupts. When critical_exit() decrements the counter to 0 it effectively calls a routine to deal with whatever interrupts were deferred during the time the code was operating in a critical section. Other architectures are unaffected. * fork_exit() has been conditionalized to remove MD assumptions for the new code. Old code will still use the old MD assumptions in regards to hard interrupt disablement. In STAGE-2 this will be turned into a subroutine call into MD code rather then hardcoded in MI code. The new code places the burden of entering the critical section in the trampoline code where it belongs. * I386: interrupts are now enabled while we are in a critical section. The interrupt vector code has been adjusted to deal with the fact. If it detects that we are in a critical section it currently defers the interrupt by adding the appropriate bit to an interrupt mask. * In order to accomplish the deferral, icu_lock is required. This is i386-specific. Thus icu_lock can only be obtained by mainline i386 code while interrupts are hard disabled. This change has been made. * Because interrupts may or may not be hard disabled during a context switch, cpu_switch() can no longer simply assume that PSL_I will be in a consistent state. Therefore, it now saves and restores eflags. * FAST INTERRUPT PROVISION. Fast interrupts are currently deferred. The intention is to eventually allow them to operate either while we are in a critical section or, if we are able to restrict the use of sched_lock, while we are not holding the sched_lock. * ICU and APIC vector assembly for I386 cleaned up. The ICU code has been cleaned up to match the APIC code in regards to format and macro availability. Additionally, the code has been adjusted to deal with deferred interrupts. * Deferred interrupts use a per-cpu boolean int_pending, and masks ipending, spending, and fpending. Being per-cpu variables it is not currently necessary to lock; bus cycles modifying them. Note that the same mechanism will enable preemption to be incorporated as a true software interrupt without having to further hack up the critical nesting code. * Note: the old critical_enter() code in kern/kern_switch.c is currently #ifdef to be compatible with both the old and new methodology. In STAGE-2 it will be moved entirely to MD code. Performance issues: One of the purposes of this commit is to enhance critical section performance, specifically to greatly reduce bus overhead to allow the critical section code to be used to protect per-cpu caches. These caches, such as Jeff's slab allocator work, can potentially operate very quickly making the effective savings of the new critical section code's performance very significant. The second purpose of this commit is to allow architectures to enable certain interrupts while in a critical section. Specifically, the intention is to eventually allow certain FAST interrupts to operate rather then defer. The third purpose of this commit is to begin to clean up the critical_enter()/critical_exit()/cpu_critical_enter()/ cpu_critical_exit() API which currently has serious cross pollution in MI code (in fork_exit() and ast() for example). The fourth purpose of this commit is to provide a framework that allows kernel-preempting software interrupts to be implemented cleanly. This is currently used for two forward interrupts in I386. Other architectures will have the choice of using this infrastructure or building the functionality directly into critical_enter()/ critical_exit(). Finally, this commit is designed to greatly improve the flexibility of various architectures to manage critical section handling, software interrupts, preemption, and other highly integrated architecture-specific details. |
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| bin | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| kerberosIV | ||
| lib | ||
| libexec | ||
| release | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| COPYRIGHT | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.upgrade | ||
| README | ||
| UPDATING | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you have to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/i386/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/User commands. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberosIV Kerberos package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/handbook/synching.html