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authorFlorian Weimer <fweimer@redhat.com>2015-11-24 17:21:01 +0100
committerFlorian Weimer <fweimer@redhat.com>2015-11-24 17:21:01 +0100
commit2359035ac52db69eb427c3b4b9d9297c98d2b225 (patch)
tree61cd8b4054f8f708b4d41b9427a989f547cf3a0c /NEWS
parentc100dca32a6859a47789ddcbb5679e74f8d92a41 (diff)
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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.
Diffstat (limited to 'NEWS')
-rw-r--r--NEWS8
1 files changed, 8 insertions, 0 deletions
diff --git a/NEWS b/NEWS
index df8ad62..cb61a3a 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,14 @@ using `glibc' in the "product" field.
Version 2.23
+* sched_setaffinity, pthread_setaffinity_np no longer attempt to guess the
+ kernel-internal CPU set size. This means that requests that change the
+ CPU affinity which failed before (for example, an all-ones CPU mask) will
+ now succeed. Applications that need to determine the effective CPU
+ affinities need to call sched_getaffinity or pthread_getaffinity_np after
+ setting it because the kernel can adjust it (and the previous size check
+ would not detect this in the majority of cases).
+
* The fts.h header can now be used with -D_FILE_OFFSET_BITS=64. With LFS
the following new symbols are used: fts64_children, fts64_close,
fts64_open, fts64_read and fts64_set.