Hi Michael,
see my comments below (refer also to my comments for
pthread_setaffinity_np.3).
Cheers,
Loïc.
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.TH PTHREAD_ATTR_SETAFFINITY_NP 3 2008-11-05 "Linux" "Linux Programmer's Manual"
Title looks weird on a 80x24 terminal.
.SH NAME
pthread_attr_setaffinity_np, pthread_attr_getaffinity_np \- set/get
CPU affinity of a thread
You surely mean: "CPU affinity attribute of a thread"
.SH SYNOPSIS
.nf
.B #define _GNU_SOURCE
.B #include <pthread.h>
.BI "int pthread_attr_setaffinity_np(pthread_attr_t " attr ,
.BI " size_t " cpusetsize ", const cpu_set_t *" cpuset );
.BI "int pthread_attr_getaffinity_np(pthread_attr_t " attr ,
.BI " size_t " cpusetsize ", cpu_set_t *" cpuset );
.sp
Compile and link with \fI\-pthread\fP.
.SH DESCRIPTION
The
.BR pthread_attr_setaffinity_np ()
sets the CPU affinity mask attribute of the
thread attributes object referred to by
.I attr
to the value specified in
.IR cpuset .
This attribute determines the CPU affinity mask
of a thread created using the thread attributes object
.IR attr .
The
.BR pthread_attr_getaffinity_np ()
returns the CPU affinity mask attribute of the thread attributes object
referred to by
.IR attr
in the buffer pointed to by
.IR cpuset .
The argument
.I cpusetsize
is the length (in bytes) of the buffer pointed to by
.IR cpuset .
Normally this argument would be specified as
.IR sizeof(cpu_set_t) .
The constant
.B CPU_SETSIZE
specifies a value one greater than the
maximum CPU number that can be stored in a CPU set.
For more details on CPU affinity masks,
as well as a description of a set of macros
that can be used to manipulate and inspect CPU sets, see
.BR sched_setaffinity (2)
for details.
.SH RETURN VALUE
On success, these functions return 0;
on error, they return a non-zero error number.
.SH ERRORS
.TP
.B EINVAL
.I attr
or
.I cpuset
is invalid.
I beg your pardon, but I couldn't find where those checks are performed
in the relevant glibc files... Perhaps I am not looking at the right place?
.TP
.BR EINVAL
.RB ( pthread_attr_setaffinity_np ())
.I cpuset
specified a CPU that was outside the range
permitted by the kernel data type
.\" cpumask_t
used to represent CPU sets.
.\" The raw sched_getaffinity() system call returns the size (in bytes)
.\" of the cpumask_t type.
This range is determined by the kernel configuration option
.BR CONFIG_NR_CPUS .
<check>
Hmmm. What does happen if CPU set contains no CPU physically on the
system when the thread is created? I guess pthread_create() fails?
</check>
.TP
.B EINVAL
.RB ( pthread_getaffinity_np ())
This should be: pthread_attr_getaffinity_np().
A CPU in the affinity mask of the thread attributes object referred to by
.I attr
lies outside the range specified by
.IR cpusetsize .
For the application programmer, this means that the structure I passed
for storing the CPU set wasn't big enough to store thread's CPU set
without loosing "affinity information".
.TP
.B ENOMEM
.RB ( pthread_attr_setaffinity_np ())
Could not allocate memory.
Correct. However, the glibc looks somewhat suspicious to me: I had
expected the memory allocated by iattr->cpuset to be bounded (by the
size of the underlying kernel structure).
Or perhaps I am just missing my coffeine :o
.SH VERSIONS
These functions are provided by glibc since version 2.3.4.
.SH CONFORMING TO
These functions are non-standard GNU extensions;
hence the suffix "_np" (non-portable) in the names.
.SH NOTES
In glibc 2.3.3 only,
versions of these functions were provided that did not have a
.I cpusetsize
argument.
Instead the CPU set size given to the underlying system calls was always
.IR sizeof(cpu_set_t) .
.SH SEE ALSO
.BR sched_setaffinity (2),
.BR sched_setscheduler (2),
Why the reference to sched_setscheduler()?
.BR pthread_attr_init (3),
.BR pthread_setaffinity_np (3),
.BR cpuset (7),
.BR pthreads (7)
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