glibc/manual
Florian Weimer 2359035ac5 Remove CPU set size checking from affinity functions [BZ #19143]
With current kernel versions, the check does not reliably detect that
unavailable CPUs are requested, for these reasons:

(1) The kernel will silently ignore non-allowed CPUs, that is, CPUs
    which are physically present but disallowed for the thread
    based on system configuration.

(2) Similarly, CPU bits which lack an online CPU (possible CPUs)
    are ignored.

(3) The existing probing code assumes that the CPU mask size is a
    power of two and at least 1024.  Neither has it to be a power
    of two, nor is the minimum possible value 1024, so the value
    determined is often too large.  This means that the CPU set
    size check in glibc accepts CPU bits beyond the actual hard
    system limit.

(4) Future kernel versions may not even have a fixed CPU set size.

After the removal of the probing code, the kernel still returns
EINVAL if no CPU in the requested set remains which can run the
thread after the affinity change.

Applications which care about the exact affinity mask will have
to query it using sched_getaffinity after setting it.  Due to the
effects described above, this commit does not change this.

The new tests supersede tst-getcpu, which is removed.  This
addresses bug 19164 because the new tests allocate CPU sets
dynamically.

	* nptl/check-cpuset.h: Remove.
	* nptl/pthread_attr_setaffinity.c (__pthread_attr_setaffinity_new):
	Remove CPU set size check.
	* nptl/pthread_setattr_default_np.c (pthread_setattr_default_np):
	Likewise.
	* sysdeps/unix/sysv/linux/check-cpuset.h: Remove.
	* sysdeps/unix/sysv/linux/pthread_setaffinity.c
	(__kernel_cpumask_size, __determine_cpumask_size): Remove.
	(__pthread_setaffinity_new): Remove CPU set size check.
	* sysdeps/unix/sysv/linux/sched_setaffinity.c
	(__kernel_cpumask_size): Remove.
	(__sched_setaffinity_new): Remove CPU set size check.
	* manual/threads.texi (Default Thread Attributes): Remove stale
	reference to check_cpuset_attr, determine_cpumask_size in comment.
	* sysdeps/unix/sysv/linux/Makefile [$(subdir) == posix] (tests):
	Remove tst-getcpu.  Add tst-affinity, tst-affinity-pid.
	[$(subdir) == nptl] (tests): Add tst-thread-affinity-pthread,
	tst-thread-affinity-pthread2, tst-thread-affinity-sched.
	* sysdeps/unix/sysv/linux/tst-affinity.c: New file.
	* sysdeps/unix/sysv/linux/tst-affinity-pid.c: New file.
	* sysdeps/unix/sysv/linux/tst-skeleton-affinity.c: New skeleton test file.
	* sysdeps/unix/sysv/linux/tst-thread-affinity-sched.c: New file.
	* sysdeps/unix/sysv/linux/tst-thread-affinity-pthread.c: New file.
	* sysdeps/unix/sysv/linux/tst-thread-affinity-pthread2.c: New file.
	* sysdeps/unix/sysv/linux/tst-thread-skeleton-affinity.c: New
	skeleton test file.
	* sysdeps/unix/sysv/linux/tst-getcpu.c: Remove.  Superseded by
	tst-affinity-pid.
2015-11-24 17:21:01 +01:00
..
examples Convert 29 more function definitions to prototype style (multiple parameters in one K&R parameter declaration). 2015-10-20 11:52:27 +00:00
argp.texi manual/argp.texi (Specifying Argp Parsers): Fix typo. 2015-10-14 11:49:58 -04:00
arith.texi
charset.texi
check-safety.sh
conf.texi
contrib.texi
creature.texi
crypt.texi
ctype.texi
debug.texi
dir
errno.texi
fdl-1.3.texi
filesys.texi Fix manual argument order for posix_fallocate64 (Bug 19086). 2015-10-07 14:10:43 -04:00
freemanuals.texi
getopt.texi
header.texi
install-plain.texi
install.texi Require GCC 4.7 or later to build glibc. 2015-10-27 16:34:12 +00:00
intro.texi
io.texi
ipc.texi
job.texi
lang.texi
lgpl-2.1.texi
libc-texinfo.sh
libc.texinfo
libcbook.texi
libdl.texi
libm-err-tab.pl
llio.texi
locale.texi
macros.texi
maint.texi
Makefile manual: skip build when perl is unavailable 2015-08-21 17:10:59 -04:00
math.texi
memory.texi malloc: Rewrite with explicit TLS access using __thread 2015-10-17 12:06:48 +02:00
message.texi
nss.texi
nsswitch.texi
pattern.texi
pipe.texi
platform.texi
probes.texi
process.texi
resource.texi
search.texi
setjmp.texi
signal.texi
socket.texi
startup.texi
stdio-fp.c
stdio.texi The va_list pointer is unspecified after a call to vfprintf [BZ #18982] 2015-10-17 12:02:22 +02:00
string.texi
summary.awk
sysinfo.texi
syslog.texi
terminal.texi
texinfo.tex
texis.awk
threads.texi Remove CPU set size checking from affinity functions [BZ #19143] 2015-11-24 17:21:01 +01:00
time.texi
tsort.awk
users.texi
xtract-typefun.awk