bind_to_cpu(3) [osf1 man page]
bind_to_cpu(3) Library Functions Manual bind_to_cpu(3) NAME
bind_to_cpu - Bind execution to a specific CPU. LIBRARY
Mach Library (libmach.a) SYNOPSIS
#include <sys/types.h> #include <sys/resource.h> int bind_to_cpu( pid_t pid, unsigned long cpu_mask , unsigned long flag ); PARAMETERS
Specifies the target pid. You must have access rights to the pid. Specifies the CPU on which the thread should run. The target CPU is the bit index in the mask. If you set more than one bit, an error is generated. A cpu_mask of zero clears any previously set CPU binding. Specifies options to CPU binding. Currently only the option BIND_NO_INHERIT is supported. When set, this option causes child processes and threads to not inherit the CPU binding. DESCRIPTION
Upon return from bind_to_cpu, all threads of the target pid are running on the target CPU. Bound threads are not eligible for execution on any other CPU. You release CPU binding by invoking bind_to_cpu with a cpu_mask of zero. EXAMPLES
/* * Fork child process and force it to run on cpu number 3. * Processes created by the forked child will not inherit bindings. */ #include <sys/resource.h> #include <sys/sysinfo.h> #include <sys/signal.h> #include <sys/types.h> #define CPU_3 0x8 /* Bit 3 set */ main() { pid_t pid; if (pid = fork()) { /* parent */ if (bind_to_cpu(pid, CPU_3, BIND_NO_INHERIT)) { kill(pid, SIGKILL); exit(1); /* bind_to_cpu() will print error msg */ } sleep(2); /* wait for child to print CPU */ } else { /* child */ long cpu_num; sleep(1); /* wait for parent to bind CPU */ getsysinfo(GSI_CURRENT_CPU, &cpu_num, 0L, 0L, 0L); printf("child running on CPU %d ", cpu_num); } } In this example, the CPU_3 symbol is defined so that bit three in the bit mask is set. When the pid returned from the fork routine identi- fies the parent routine, the bind_to_cpu routine is called. This routine binds the child process to CPU number three, as specified in the CPU_3 symbol. When the pid returned from the fork routine identifies the child routine, the child routine sleeps to give the parent routine time to set its CPU binding. Then it uses the getsysinfo call to determine its CPU and displays its CPU with the printf routine. If the return value from the bind_to_cpu routine indicates an error, the parent process kills the child process and exits with an error status. RETURN VALUES
Upon successful completion, bind_to_cpu returns zero. Upon error, a -1 is returned. RELATED INFORMATION
Commands: runon(1) Functions: getsysinfo(2) delim off bind_to_cpu(3)
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SCHED_SETAFFINITY(2) Linux Programmer's Manual SCHED_SETAFFINITY(2) NAME
sched_setaffinity, sched_getaffinity - set and get a process's CPU affinity mask SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sched.h> int sched_setaffinity(pid_t pid, size_t cpusetsize, cpu_set_t *mask); int sched_getaffinity(pid_t pid, size_t cpusetsize, cpu_set_t *mask); DESCRIPTION
A process's CPU affinity mask determines the set of CPUs on which it is eligible to run. On a multiprocessor system, setting the CPU affinity mask can be used to obtain performance benefits. For example, by dedicating one CPU to a particular process (i.e., setting the affinity mask of that process to specify a single CPU, and setting the affinity mask of all other processes to exclude that CPU), it is possible to ensure maximum execution speed for that process. Restricting a process to run on a single CPU also avoids the performance cost caused by the cache invalidation that occurs when a process ceases to execute on one CPU and then recommences execution on a different CPU. A CPU affinity mask is represented by the cpu_set_t structure, a "CPU set", pointed to by mask. A set of macros for manipulating CPU sets is described in CPU_SET(3). sched_setaffinity() sets the CPU affinity mask of the process whose ID is pid to the value specified by mask. If pid is zero, then the calling process is used. The argument cpusetsize is the length (in bytes) of the data pointed to by mask. Normally this argument would be specified as sizeof(cpu_set_t). If the process specified by pid is not currently running on one of the CPUs specified in mask, then that process is migrated to one of the CPUs specified in mask. sched_getaffinity() writes the affinity mask of the process whose ID is pid into the cpu_set_t structure pointed to by mask. The cpuset- size argument specifies the size (in bytes) of mask. If pid is zero, then the mask of the calling process is returned. RETURN VALUE
On success, sched_setaffinity() and sched_getaffinity() return 0. On error, -1 is returned, and errno is set appropriately. ERRORS
EFAULT A supplied memory address was invalid. EINVAL The affinity bit mask mask contains no processors that are currently physically on the system and permitted to the process according to any restrictions that may be imposed by the "cpuset" mechanism described in cpuset(7). EINVAL (sched_getaffinity() and, in kernels before 2.6.9, sched_setaffinity()) cpusetsize is smaller than the size of the affinity mask used by the kernel. EPERM (sched_setaffinity()) The calling process does not have appropriate privileges. The caller needs an effective user ID equal to the user ID or effective user ID of the process identified by pid, or it must possess the CAP_SYS_NICE capability. ESRCH The process whose ID is pid could not be found. VERSIONS
The CPU affinity system calls were introduced in Linux kernel 2.5.8. The system call wrappers were introduced in glibc 2.3. Initially, the glibc interfaces included a cpusetsize argument, typed as unsigned int. In glibc 2.3.3, the cpusetsize argument was removed, but was then restored in glibc 2.3.4, with type size_t. CONFORMING TO
These system calls are Linux-specific. NOTES
After a call to sched_setaffinity(), the set of CPUs on which the process will actually run is the intersection of the set specified in the mask argument and the set of CPUs actually present on the system. The system may further restrict the set of CPUs on which the process runs if the "cpuset" mechanism described in cpuset(7) is being used. These restrictions on the actual set of CPUs on which the process will run are silently imposed by the kernel. sched_setscheduler(2) has a description of the Linux scheduling scheme. The affinity mask is actually a per-thread attribute that can be adjusted independently for each of the threads in a thread group. The value returned from a call to gettid(2) can be passed in the argument pid. Specifying pid as 0 will set the attribute for the calling thread, and passing the value returned from a call to getpid(2) will set the attribute for the main thread of the thread group. (If you are using the POSIX threads API, then use pthread_setaffinity_np(3) instead of sched_setaffinity().) A child created via fork(2) inherits its parent's CPU affinity mask. The affinity mask is preserved across an execve(2). This manual page describes the glibc interface for the CPU affinity calls. The actual system call interface is slightly different, with the mask being typed as unsigned long *, reflecting the fact that the underlying implementation of CPU sets is a simple bit mask. On suc- cess, the raw sched_getaffinity() system call returns the size (in bytes) of the cpumask_t data type that is used internally by the kernel to represent the CPU set bit mask. SEE ALSO
clone(2), getcpu(2), getpriority(2), gettid(2), nice(2), sched_get_priority_max(2), sched_get_priority_min(2), sched_getscheduler(2), sched_setscheduler(2), setpriority(2), CPU_SET(3), sched_getcpu(3), capabilities(7), pthread_setaffinity_np(3), cpuset(7) COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2010-09-10 SCHED_SETAFFINITY(2)