config ARCH string option env="ARCH" config KERNELVERSION string option env="KERNELVERSION" config DEFCONFIG_LIST string depends on !UML option defconfig_list default "/lib/modules/$UNAME_RELEASE/.config" default "/etc/kernel-config" default "/boot/config-$UNAME_RELEASE" default "$ARCH_DEFCONFIG" default "arch/$ARCH/defconfig" config CONSTRUCTORS bool depends on !UML config HAVE_IRQ_WORK bool config IRQ_WORK bool depends on HAVE_IRQ_WORK menu "General setup" config EXPERIMENTAL bool "Prompt for development and/or incomplete code/drivers" ---help--- Some of the various things that Linux supports (such as network drivers, file systems, network protocols, etc.) can be in a state of development where the functionality, stability, or the level of testing is not yet high enough for general use. This is usually known as the "alpha-test" phase among developers. If a feature is currently in alpha-test, then the developers usually discourage uninformed widespread use of this feature by the general public to avoid "Why doesn't this work?" type mail messages. However, active testing and use of these systems is welcomed. Just be aware that it may not meet the normal level of reliability or it may fail to work in some special cases. Detailed bug reports from people familiar with the kernel internals are usually welcomed by the developers (before submitting bug reports, please read the documents <file:README>, <file:MAINTAINERS>, <file:REPORTING-BUGS>, <file:Documentation/BUG-HUNTING>, and <file:Documentation/oops-tracing.txt> in the kernel source). This option will also make obsoleted drivers available. These are drivers that have been replaced by something else, and/or are scheduled to be removed in a future kernel release. Unless you intend to help test and develop a feature or driver that falls into this category, or you have a situation that requires using these features, you should probably say N here, which will cause the configurator to present you with fewer choices. If you say Y here, you will be offered the choice of using features or drivers that are currently considered to be in the alpha-test phase. config BROKEN bool config BROKEN_ON_SMP bool depends on BROKEN || !SMP default y config INIT_ENV_ARG_LIMIT int default 32 if !UML default 128 if UML help Maximum of each of the number of arguments and environment variables passed to init from the kernel command line. config CROSS_COMPILE string "Cross-compiler tool prefix" help Same as running 'make CROSS_COMPILE=prefix-' but stored for default make runs in this kernel build directory. You don't need to set this unless you want the configured kernel build directory to select the cross-compiler automatically. config LOCALVERSION string "Local version - append to kernel release" help Append an extra string to the end of your kernel version. This will show up when you type uname, for example. The string you set here will be appended after the contents of any files with a filename matching localversion* in your object and source tree, in that order. Your total string can be a maximum of 64 characters. config LOCALVERSION_AUTO bool "Automatically append version information to the version string" default y help This will try to automatically determine if the current tree is a release tree by looking for git tags that belong to the current top of tree revision. A string of the format -gxxxxxxxx will be added to the localversion if a git-based tree is found. The string generated by this will be appended after any matching localversion* files, and after the value set in CONFIG_LOCALVERSION. (The actual string used here is the first eight characters produced by running the command: $ git rev-parse --verify HEAD which is done within the script "scripts/setlocalversion".) config HAVE_KERNEL_GZIP bool config HAVE_KERNEL_BZIP2 bool config HAVE_KERNEL_LZMA bool config HAVE_KERNEL_XZ bool config HAVE_KERNEL_LZO bool choice prompt "Kernel compression mode" default KERNEL_GZIP depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO help The linux kernel is a kind of self-extracting executable. Several compression algorithms are available, which differ in efficiency, compression and decompression speed. Compression speed is only relevant when building a kernel. Decompression speed is relevant at each boot. If you have any problems with bzip2 or lzma compressed kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older version of this functionality (bzip2 only), for 2.4, was supplied by Christian Ludwig) High compression options are mostly useful for users, who are low on disk space (embedded systems), but for whom ram size matters less. If in doubt, select 'gzip' config KERNEL_GZIP bool "Gzip" depends on HAVE_KERNEL_GZIP help The old and tried gzip compression. It provides a good balance between compression ratio and decompression speed. config KERNEL_BZIP2 bool "Bzip2" depends on HAVE_KERNEL_BZIP2 help Its compression ratio and speed is intermediate. Decompression speed is slowest among the three. The kernel size is about 10% smaller with bzip2, in comparison to gzip. Bzip2 uses a large amount of memory. For modern kernels you will need at least 8MB RAM or more for booting. config KERNEL_LZMA bool "LZMA" depends on HAVE_KERNEL_LZMA help The most recent compression algorithm. Its ratio is best, decompression speed is between the other two. Compression is slowest. The kernel size is about 33% smaller with LZMA in comparison to gzip. config KERNEL_XZ bool "XZ" depends on HAVE_KERNEL_XZ help XZ uses the LZMA2 algorithm and instruction set specific BCJ filters which can improve compression ratio of executable code. The size of the kernel is about 30% smaller with XZ in comparison to gzip. On architectures for which there is a BCJ filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ will create a few percent smaller kernel than plain LZMA. The speed is about the same as with LZMA: The decompression speed of XZ is better than that of bzip2 but worse than gzip and LZO. Compression is slow. config KERNEL_LZO bool "LZO" depends on HAVE_KERNEL_LZO help Its compression ratio is the poorest among the 4. The kernel size is about 10% bigger than gzip; however its speed (both compression and decompression) is the fastest. endchoice config DEFAULT_HOSTNAME string "Default hostname" default "(none)" help This option determines the default system hostname before userspace calls sethostname(2). The kernel traditionally uses "(none)" here, but you may wish to use a different default here to make a minimal system more usable with less configuration. config SWAP bool "Support for paging of anonymous memory (swap)" depends on MMU && BLOCK default y help This option allows you to choose whether you want to have support for so called swap devices or swap files in your kernel that are used to provide more virtual memory than the actual RAM present in your computer. If unsure say Y. config SYSVIPC bool "System V IPC" ---help--- Inter Process Communication is a suite of library functions and system calls which let processes (running programs) synchronize and exchange information. It is generally considered to be a good thing, and some programs won't run unless you say Y here. In particular, if you want to run the DOS emulator dosemu under Linux (read the DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), you'll need to say Y here. You can find documentation about IPC with "info ipc" and also in section 6.4 of the Linux Programmer's Guide, available from <http://www.tldp.org/guides.html>. config SYSVIPC_SYSCTL bool depends on SYSVIPC depends on SYSCTL default y config POSIX_MQUEUE bool "POSIX Message Queues" depends on NET && EXPERIMENTAL ---help--- POSIX variant of message queues is a part of IPC. In POSIX message queues every message has a priority which decides about succession of receiving it by a process. If you want to compile and run programs written e.g. for Solaris with use of its POSIX message queues (functions mq_*) say Y here. POSIX message queues are visible as a filesystem called 'mqueue' and can be mounted somewhere if you want to do filesystem operations on message queues. If unsure, say Y. config POSIX_MQUEUE_SYSCTL bool depends on POSIX_MQUEUE depends on SYSCTL default y config BSD_PROCESS_ACCT bool "BSD Process Accounting" help If you say Y here, a user level program will be able to instruct the kernel (via a special system call) to write process accounting information to a file: whenever a process exits, information about that process will be appended to the file by the kernel. The information includes things such as creation time, owning user, command name, memory usage, controlling terminal etc. (the complete list is in the struct acct in <file:include/linux/acct.h>). It is up to the user level program to do useful things with this information. This is generally a good idea, so say Y. config BSD_PROCESS_ACCT_V3 bool "BSD Process Accounting version 3 file format" depends on BSD_PROCESS_ACCT default n help If you say Y here, the process accounting information is written in a new file format that also logs the process IDs of each process and it's parent. Note that this file format is incompatible with previous v0/v1/v2 file formats, so you will need updated tools for processing it. A preliminary version of these tools is available at <http://www.gnu.org/software/acct/>. config FHANDLE bool "open by fhandle syscalls" select EXPORTFS help If you say Y here, a user level program will be able to map file names to handle and then later use the handle for different file system operations. This is useful in implementing userspace file servers, which now track files using handles instead of names. The handle would remain the same even if file names get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) syscalls. config TASKSTATS bool "Export task/process statistics through netlink (EXPERIMENTAL)" depends on NET default n help Export selected statistics for tasks/processes through the generic netlink interface. Unlike BSD process accounting, the statistics are available during the lifetime of tasks/processes as responses to commands. Like BSD accounting, they are sent to user space on task exit. Say N if unsure. config TASK_DELAY_ACCT bool "Enable per-task delay accounting (EXPERIMENTAL)" depends on TASKSTATS help Collect information on time spent by a task waiting for system resources like cpu, synchronous block I/O completion and swapping in pages. Such statistics can help in setting a task's priorities relative to other tasks for cpu, io, rss limits etc. Say N if unsure. config TASK_XACCT bool "Enable extended accounting over taskstats (EXPERIMENTAL)" depends on TASKSTATS help Collect extended task accounting data and send the data to userland for processing over the taskstats interface. Say N if unsure. config TASK_IO_ACCOUNTING bool "Enable per-task storage I/O accounting (EXPERIMENTAL)" depends on TASK_XACCT help Collect information on the number of bytes of storage I/O which this task has caused. Say N if unsure. config AUDIT bool "Auditing support" depends on NET help Enable auditing infrastructure that can be used with another kernel subsystem, such as SELinux (which requires this for logging of avc messages output). Does not do system-call auditing without CONFIG_AUDITSYSCALL. config AUDITSYSCALL bool "Enable system-call auditing support" depends on AUDIT && (X86 || PPC || S390 || IA64 || UML || SPARC64 || SUPERH) default y if SECURITY_SELINUX help Enable low-overhead system-call auditing infrastructure that can be used independently or with another kernel subsystem, such as SELinux. config AUDIT_WATCH def_bool y depends on AUDITSYSCALL select FSNOTIFY config AUDIT_TREE def_bool y depends on AUDITSYSCALL select FSNOTIFY source "kernel/irq/Kconfig" menu "RCU Subsystem" choice prompt "RCU Implementation" default TREE_RCU config TREE_RCU bool "Tree-based hierarchical RCU" depends on !PREEMPT && SMP help This option selects the RCU implementation that is designed for very large SMP system with hundreds or thousands of CPUs. It also scales down nicely to smaller systems. config TREE_PREEMPT_RCU bool "Preemptible tree-based hierarchical RCU" depends on PREEMPT && SMP help This option selects the RCU implementation that is designed for very large SMP systems with hundreds or thousands of CPUs, but for which real-time response is also required. It also scales down nicely to smaller systems. config TINY_RCU bool "UP-only small-memory-footprint RCU" depends on !PREEMPT && !SMP help This option selects the RCU implementation that is designed for UP systems from which real-time response is not required. This option greatly reduces the memory footprint of RCU. config TINY_PREEMPT_RCU bool "Preemptible UP-only small-memory-footprint RCU" depends on PREEMPT && !SMP help This option selects the RCU implementation that is designed for real-time UP systems. This option greatly reduces the memory footprint of RCU. endchoice config PREEMPT_RCU def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU ) help This option enables preemptible-RCU code that is common between the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations. config RCU_TRACE bool "Enable tracing for RCU" help This option provides tracing in RCU which presents stats in debugfs for debugging RCU implementation. Say Y here if you want to enable RCU tracing Say N if you are unsure. config RCU_FANOUT int "Tree-based hierarchical RCU fanout value" range 2 64 if 64BIT range 2 32 if !64BIT depends on TREE_RCU || TREE_PREEMPT_RCU default 64 if 64BIT default 32 if !64BIT help This option controls the fanout of hierarchical implementations of RCU, allowing RCU to work efficiently on machines with large numbers of CPUs. This value must be at least the fourth root of NR_CPUS, which allows NR_CPUS to be insanely large. The default value of RCU_FANOUT should be used for production systems, but if you are stress-testing the RCU implementation itself, small RCU_FANOUT values allow you to test large-system code paths on small(er) systems. Select a specific number if testing RCU itself. Take the default if unsure. config RCU_FANOUT_EXACT bool "Disable tree-based hierarchical RCU auto-balancing" depends on TREE_RCU || TREE_PREEMPT_RCU default n help This option forces use of the exact RCU_FANOUT value specified, regardless of imbalances in the hierarchy. This is useful for testing RCU itself, and might one day be useful on systems with strong NUMA behavior. Without RCU_FANOUT_EXACT, the code will balance the hierarchy. Say N if unsure. config RCU_FAST_NO_HZ bool "Accelerate last non-dyntick-idle CPU's grace periods" depends on TREE_RCU && NO_HZ && SMP default n help This option causes RCU to attempt to accelerate grace periods in order to allow the final CPU to enter dynticks-idle state more quickly. On the other hand, this option increases the overhead of the dynticks-idle checking, particularly on systems with large numbers of CPUs. Say Y if energy efficiency is critically important, particularly if you have relatively few CPUs. Say N if you are unsure. config TREE_RCU_TRACE def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU ) select DEBUG_FS help This option provides tracing for the TREE_RCU and TREE_PREEMPT_RCU implementations, permitting Makefile to trivially select kernel/rcutree_trace.c. config RCU_BOOST bool "Enable RCU priority boosting" depends on RT_MUTEXES && PREEMPT_RCU default n help This option boosts the priority of preempted RCU readers that block the current preemptible RCU grace period for too long.Lines 1–500 of 1413. Load more
config ARCH string option env="ARCH" config KERNELVERSION string option env="KERNELVERSION" config DEFCONFIG_LIST string depends on !UML option defconfig_list default "/lib/modules/$UNAME_RELEASE/.config" default "/etc/kernel-config" default "/boot/config-$UNAME_RELEASE" default "$ARCH_DEFCONFIG" default "arch/$ARCH/defconfig" config CONSTRUCTORS bool depends on !UML config HAVE_IRQ_WORK bool config IRQ_WORK bool depends on HAVE_IRQ_WORK menu "General setup" config EXPERIMENTAL bool "Prompt for development and/or incomplete code/drivers" ---help--- Some of the various things that Linux supports (such as network drivers, file systems, network protocols, etc.) can be in a state of development where the functionality, stability, or the level of testing is not yet high enough for general use. This is usually known as the "alpha-test" phase among developers. If a feature is currently in alpha-test, then the developers usually discourage uninformed widespread use of this feature by the general public to avoid "Why doesn't this work?" type mail messages. However, active testing and use of these systems is welcomed. Just be aware that it may not meet the normal level of reliability or it may fail to work in some special cases. Detailed bug reports from people familiar with the kernel internals are usually welcomed by the developers (before submitting bug reports, please read the documents <file:README>, <file:MAINTAINERS>, <file:REPORTING-BUGS>, <file:Documentation/BUG-HUNTING>, and <file:Documentation/oops-tracing.txt> in the kernel source). This option will also make obsoleted drivers available. These are drivers that have been replaced by something else, and/or are scheduled to be removed in a future kernel release. Unless you intend to help test and develop a feature or driver that falls into this category, or you have a situation that requires using these features, you should probably say N here, which will cause the configurator to present you with fewer choices. If you say Y here, you will be offered the choice of using features or drivers that are currently considered to be in the alpha-test phase. config BROKEN bool config BROKEN_ON_SMP bool depends on BROKEN || !SMP default y config INIT_ENV_ARG_LIMIT int default 32 if !UML default 128 if UML help Maximum of each of the number of arguments and environment variables passed to init from the kernel command line. config CROSS_COMPILE string "Cross-compiler tool prefix" help Same as running 'make CROSS_COMPILE=prefix-' but stored for default make runs in this kernel build directory. You don't need to set this unless you want the configured kernel build directory to select the cross-compiler automatically. config LOCALVERSION string "Local version - append to kernel release" help Append an extra string to the end of your kernel version. This will show up when you type uname, for example. The string you set here will be appended after the contents of any files with a filename matching localversion* in your object and source tree, in that order. Your total string can be a maximum of 64 characters. config LOCALVERSION_AUTO bool "Automatically append version information to the version string" default y help This will try to automatically determine if the current tree is a release tree by looking for git tags that belong to the current top of tree revision. A string of the format -gxxxxxxxx will be added to the localversion if a git-based tree is found. The string generated by this will be appended after any matching localversion* files, and after the value set in CONFIG_LOCALVERSION. (The actual string used here is the first eight characters produced by running the command: $ git rev-parse --verify HEAD which is done within the script "scripts/setlocalversion".) config HAVE_KERNEL_GZIP bool config HAVE_KERNEL_BZIP2 bool config HAVE_KERNEL_LZMA bool config HAVE_KERNEL_XZ bool config HAVE_KERNEL_LZO bool choice prompt "Kernel compression mode" default KERNEL_GZIP depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO help The linux kernel is a kind of self-extracting executable. Several compression algorithms are available, which differ in efficiency, compression and decompression speed. Compression speed is only relevant when building a kernel. Decompression speed is relevant at each boot. If you have any problems with bzip2 or lzma compressed kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older version of this functionality (bzip2 only), for 2.4, was supplied by Christian Ludwig) High compression options are mostly useful for users, who are low on disk space (embedded systems), but for whom ram size matters less. If in doubt, select 'gzip' config KERNEL_GZIP bool "Gzip" depends on HAVE_KERNEL_GZIP help The old and tried gzip compression. It provides a good balance between compression ratio and decompression speed. config KERNEL_BZIP2 bool "Bzip2" depends on HAVE_KERNEL_BZIP2 help Its compression ratio and speed is intermediate. Decompression speed is slowest among the three. The kernel size is about 10% smaller with bzip2, in comparison to gzip. Bzip2 uses a large amount of memory. For modern kernels you will need at least 8MB RAM or more for booting. config KERNEL_LZMA bool "LZMA" depends on HAVE_KERNEL_LZMA help The most recent compression algorithm. Its ratio is best, decompression speed is between the other two. Compression is slowest. The kernel size is about 33% smaller with LZMA in comparison to gzip. config KERNEL_XZ bool "XZ" depends on HAVE_KERNEL_XZ help XZ uses the LZMA2 algorithm and instruction set specific BCJ filters which can improve compression ratio of executable code. The size of the kernel is about 30% smaller with XZ in comparison to gzip. On architectures for which there is a BCJ filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ will create a few percent smaller kernel than plain LZMA. The speed is about the same as with LZMA: The decompression speed of XZ is better than that of bzip2 but worse than gzip and LZO. Compression is slow. config KERNEL_LZO bool "LZO" depends on HAVE_KERNEL_LZO help Its compression ratio is the poorest among the 4. The kernel size is about 10% bigger than gzip; however its speed (both compression and decompression) is the fastest. endchoice config DEFAULT_HOSTNAME string "Default hostname" default "(none)" help This option determines the default system hostname before userspace calls sethostname(2). The kernel traditionally uses "(none)" here, but you may wish to use a different default here to make a minimal system more usable with less configuration. config SWAP bool "Support for paging of anonymous memory (swap)" depends on MMU && BLOCK default y help This option allows you to choose whether you want to have support for so called swap devices or swap files in your kernel that are used to provide more virtual memory than the actual RAM present in your computer. If unsure say Y. config SYSVIPC bool "System V IPC" ---help--- Inter Process Communication is a suite of library functions and system calls which let processes (running programs) synchronize and exchange information. It is generally considered to be a good thing, and some programs won't run unless you say Y here. In particular, if you want to run the DOS emulator dosemu under Linux (read the DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), you'll need to say Y here. You can find documentation about IPC with "info ipc" and also in section 6.4 of the Linux Programmer's Guide, available from <http://www.tldp.org/guides.html>. config SYSVIPC_SYSCTL bool depends on SYSVIPC depends on SYSCTL default y config POSIX_MQUEUE bool "POSIX Message Queues" depends on NET && EXPERIMENTAL ---help--- POSIX variant of message queues is a part of IPC. In POSIX message queues every message has a priority which decides about succession of receiving it by a process. If you want to compile and run programs written e.g. for Solaris with use of its POSIX message queues (functions mq_*) say Y here. POSIX message queues are visible as a filesystem called 'mqueue' and can be mounted somewhere if you want to do filesystem operations on message queues. If unsure, say Y. config POSIX_MQUEUE_SYSCTL bool depends on POSIX_MQUEUE depends on SYSCTL default y config BSD_PROCESS_ACCT bool "BSD Process Accounting" help If you say Y here, a user level program will be able to instruct the kernel (via a special system call) to write process accounting information to a file: whenever a process exits, information about that process will be appended to the file by the kernel. The information includes things such as creation time, owning user, command name, memory usage, controlling terminal etc. (the complete list is in the struct acct in <file:include/linux/acct.h>). It is up to the user level program to do useful things with this information. This is generally a good idea, so say Y. config BSD_PROCESS_ACCT_V3 bool "BSD Process Accounting version 3 file format" depends on BSD_PROCESS_ACCT default n help If you say Y here, the process accounting information is written in a new file format that also logs the process IDs of each process and it's parent. Note that this file format is incompatible with previous v0/v1/v2 file formats, so you will need updated tools for processing it. A preliminary version of these tools is available at <http://www.gnu.org/software/acct/>. config FHANDLE bool "open by fhandle syscalls" select EXPORTFS help If you say Y here, a user level program will be able to map file names to handle and then later use the handle for different file system operations. This is useful in implementing userspace file servers, which now track files using handles instead of names. The handle would remain the same even if file names get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) syscalls. config TASKSTATS bool "Export task/process statistics through netlink (EXPERIMENTAL)" depends on NET default n help Export selected statistics for tasks/processes through the generic netlink interface. Unlike BSD process accounting, the statistics are available during the lifetime of tasks/processes as responses to commands. Like BSD accounting, they are sent to user space on task exit. Say N if unsure. config TASK_DELAY_ACCT bool "Enable per-task delay accounting (EXPERIMENTAL)" depends on TASKSTATS help Collect information on time spent by a task waiting for system resources like cpu, synchronous block I/O completion and swapping in pages. Such statistics can help in setting a task's priorities relative to other tasks for cpu, io, rss limits etc. Say N if unsure. config TASK_XACCT bool "Enable extended accounting over taskstats (EXPERIMENTAL)" depends on TASKSTATS help Collect extended task accounting data and send the data to userland for processing over the taskstats interface. Say N if unsure. config TASK_IO_ACCOUNTING bool "Enable per-task storage I/O accounting (EXPERIMENTAL)" depends on TASK_XACCT help Collect information on the number of bytes of storage I/O which this task has caused. Say N if unsure. config AUDIT bool "Auditing support" depends on NET help Enable auditing infrastructure that can be used with another kernel subsystem, such as SELinux (which requires this for logging of avc messages output). Does not do system-call auditing without CONFIG_AUDITSYSCALL. config AUDITSYSCALL bool "Enable system-call auditing support" depends on AUDIT && (X86 || PPC || S390 || IA64 || UML || SPARC64 || SUPERH) default y if SECURITY_SELINUX help Enable low-overhead system-call auditing infrastructure that can be used independently or with another kernel subsystem, such as SELinux. config AUDIT_WATCH def_bool y depends on AUDITSYSCALL select FSNOTIFY config AUDIT_TREE def_bool y depends on AUDITSYSCALL select FSNOTIFY source "kernel/irq/Kconfig" menu "RCU Subsystem" choice prompt "RCU Implementation" default TREE_RCU config TREE_RCU bool "Tree-based hierarchical RCU" depends on !PREEMPT && SMP help This option selects the RCU implementation that is designed for very large SMP system with hundreds or thousands of CPUs. It also scales down nicely to smaller systems. config TREE_PREEMPT_RCU bool "Preemptible tree-based hierarchical RCU" depends on PREEMPT && SMP help This option selects the RCU implementation that is designed for very large SMP systems with hundreds or thousands of CPUs, but for which real-time response is also required. It also scales down nicely to smaller systems. config TINY_RCU bool "UP-only small-memory-footprint RCU" depends on !PREEMPT && !SMP help This option selects the RCU implementation that is designed for UP systems from which real-time response is not required. This option greatly reduces the memory footprint of RCU. config TINY_PREEMPT_RCU bool "Preemptible UP-only small-memory-footprint RCU" depends on PREEMPT && !SMP help This option selects the RCU implementation that is designed for real-time UP systems. This option greatly reduces the memory footprint of RCU. endchoice config PREEMPT_RCU def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU ) help This option enables preemptible-RCU code that is common between the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations. config RCU_TRACE bool "Enable tracing for RCU" help This option provides tracing in RCU which presents stats in debugfs for debugging RCU implementation. Say Y here if you want to enable RCU tracing Say N if you are unsure. config RCU_FANOUT int "Tree-based hierarchical RCU fanout value" range 2 64 if 64BIT range 2 32 if !64BIT depends on TREE_RCU || TREE_PREEMPT_RCU default 64 if 64BIT default 32 if !64BIT help This option controls the fanout of hierarchical implementations of RCU, allowing RCU to work efficiently on machines with large numbers of CPUs. This value must be at least the fourth root of NR_CPUS, which allows NR_CPUS to be insanely large. The default value of RCU_FANOUT should be used for production systems, but if you are stress-testing the RCU implementation itself, small RCU_FANOUT values allow you to test large-system code paths on small(er) systems. Select a specific number if testing RCU itself. Take the default if unsure. config RCU_FANOUT_EXACT bool "Disable tree-based hierarchical RCU auto-balancing" depends on TREE_RCU || TREE_PREEMPT_RCU default n help This option forces use of the exact RCU_FANOUT value specified, regardless of imbalances in the hierarchy. This is useful for testing RCU itself, and might one day be useful on systems with strong NUMA behavior. Without RCU_FANOUT_EXACT, the code will balance the hierarchy. Say N if unsure. config RCU_FAST_NO_HZ bool "Accelerate last non-dyntick-idle CPU's grace periods" depends on TREE_RCU && NO_HZ && SMP default n help This option causes RCU to attempt to accelerate grace periods in order to allow the final CPU to enter dynticks-idle state more quickly. On the other hand, this option increases the overhead of the dynticks-idle checking, particularly on systems with large numbers of CPUs. Say Y if energy efficiency is critically important, particularly if you have relatively few CPUs. Say N if you are unsure. config TREE_RCU_TRACE def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU ) select DEBUG_FS help This option provides tracing for the TREE_RCU and TREE_PREEMPT_RCU implementations, permitting Makefile to trivially select kernel/rcutree_trace.c. config RCU_BOOST bool "Enable RCU priority boosting" depends on RT_MUTEXES && PREEMPT_RCU default n help This option boosts the priority of preempted RCU readers that block the current preemptible RCU grace period for too long.