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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2008-11-13 21:56:39 -0500 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2008-11-25 20:53:59 -0500 |
| commit | 69241990531c46cde47ae7312abdac3d317d6e51 (patch) | |
| tree | 1416d4e9eaecde79032c6079e57163e2b8f7030a /man3 | |
| parent | b62e3548228be55c9b46f4b26f90a7065cd05090 (diff) | |
| download | man-pages-69241990531c46cde47ae7312abdac3d317d6e51.tar.gz | |
CPU_SET.3: Various improvements in DESCRIPTION
After review comments by Bert Wesarg:
* Explain that cpu_set_t is a bitset, but should be considered
opaque.
* A CPU set can be duplicated with memset().
* Size of a CPU set is rounded up to size of long.
* CPU_SETSIZE is in bits, but the setsize argument is in bytes.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Reported-by: Bert Wesarg <bert.wesarg@googlemail.com>
Reviewed-by: Bert Wesarg <bert.wesarg@googlemail.com>
Diffstat (limited to 'man3')
| -rw-r--r-- | man3/CPU_SET.3 | 32 |
1 files changed, 30 insertions, 2 deletions
diff --git a/man3/CPU_SET.3 b/man3/CPU_SET.3 index 7046fde3de..5fe9838423 100644 --- a/man3/CPU_SET.3 +++ b/man3/CPU_SET.3 @@ -82,6 +82,13 @@ CPU sets are used by .BR sched_setaffinity (2) and similar interfaces. +The +.I cpu_set_t +data type is implemented as a bitset. +However, the data structure treated as considered opaque: +all manipulation of CPU sets should be done via the macros +described in this page. + The following macros are provided to operate on the CPU set .IR set : .TP 17 @@ -177,9 +184,9 @@ in the range 0 to Return the size in bytes of the CPU set that would be needed to hold CPUs in the range 0 to .IR num_cpus-1 . -This macro provides the value that can be used for +This macro provides the value that can be used for the .I setsize -in the +argument in the .BR CPU_*_S () macros described below. .TP @@ -255,6 +262,27 @@ and first appeared in glibc 2.7. .SH "CONFORMING TO" These interfaces are Linux-specific. +.SH NOTES +To duplicate a CPU set, use +.BR memcpy (3). + +Since CPU sets are bitsets allocated in units of long words, +the actual number of CPUs in a dynamically +allocated CPU set will be rounded up to the next multiple of +.IR "sizeof(unsigned long)" . +An application should consider the contents on these extra bits +to be undefined. + +Note that the constant +.B CPU_SETSIZE +indicated the number of CPUs in the +.I cpu_set_t +data type (thus, it is effectively a count of bits in the bitset), +while the +.I setsize +argument of the +.BR CPU_*_S () +macros is a size in bytes. .SH EXAMPLE The following program demonstrates the use of some of the macros used for dynamically allocated CPU sets. |