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Use system CPU count for sysconf(_SC_NPROCESSORS_*) (#1992702)

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This commit is contained in:
Florian Weimer 2021-09-15 12:09:06 +02:00
parent 4476c131c3
commit 7d28ddf24c
4 changed files with 519 additions and 1 deletions
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102
glibc-rh1992702-1.patch Normal file
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@ -0,0 +1,102 @@
Patch proposed for upstream inclusion:
<https://sourceware.org/pipermail/libc-alpha/2021-September/130801.html>
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue Sep 7 09:22:57 2021 -0300
misc: Add __get_nprocs_sched
This is an internal function meant to return the number of avaliable
processor where the process can scheduled, different than the
__get_nprocs which returns a the system available online CPU.
The Linux implementation currently only calls __get_nprocs(), which
in tuns calls sched_getaffinity.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
diff --git a/include/sys/sysinfo.h b/include/sys/sysinfo.h
index 7388356a19269335..c490561581733038 100644
--- a/include/sys/sysinfo.h
+++ b/include/sys/sysinfo.h
@@ -9,10 +9,15 @@
extern int __get_nprocs_conf (void);
libc_hidden_proto (__get_nprocs_conf)
-/* Return number of available processors. */
+/* Return number of available processors (not all of them will be
+ available to the caller process). */
extern int __get_nprocs (void);
libc_hidden_proto (__get_nprocs)
+/* Return the number of available processors which the process can
+ be scheduled. */
+extern int __get_nprocs_sched (void) attribute_hidden;
+
/* Return number of physical pages of memory in the system. */
extern long int __get_phys_pages (void);
libc_hidden_proto (__get_phys_pages)
diff --git a/malloc/arena.c b/malloc/arena.c
index 4c398753aeadbb9d..78ef4cf18c780dfc 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -878,7 +878,7 @@ arena_get2 (size_t size, mstate avoid_arena)
narenas_limit = mp_.arena_max;
else if (narenas > mp_.arena_test)
{
- int n = __get_nprocs ();
+ int n = __get_nprocs_sched ();
if (n >= 1)
narenas_limit = NARENAS_FROM_NCORES (n);
diff --git a/misc/getsysstats.c b/misc/getsysstats.c
index 2986d62247cf98ca..5cbba0f9bd93bd78 100644
--- a/misc/getsysstats.c
+++ b/misc/getsysstats.c
@@ -44,6 +44,12 @@ weak_alias (__get_nprocs, get_nprocs)
link_warning (get_nprocs, "warning: get_nprocs will always return 1")
+int
+__get_nprocs_sched (void)
+{
+ return 1;
+}
+
long int
__get_phys_pages (void)
{
diff --git a/sysdeps/mach/getsysstats.c b/sysdeps/mach/getsysstats.c
index 1267f39da26aee38..cc8023f979bf6f74 100644
--- a/sysdeps/mach/getsysstats.c
+++ b/sysdeps/mach/getsysstats.c
@@ -62,6 +62,12 @@ __get_nprocs (void)
libc_hidden_def (__get_nprocs)
weak_alias (__get_nprocs, get_nprocs)
+int
+__get_nprocs_sched (void)
+{
+ return __get_nprocs ();
+}
+
/* Return the number of physical pages on the system. */
long int
__get_phys_pages (void)
diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c
index 8a5d342f0c8bbeae..e9c0dc4d83d4fb2a 100644
--- a/sysdeps/unix/sysv/linux/getsysstats.c
+++ b/sysdeps/unix/sysv/linux/getsysstats.c
@@ -87,6 +87,12 @@ __get_nprocs (void)
libc_hidden_def (__get_nprocs)
weak_alias (__get_nprocs, get_nprocs)
+int
+__get_nprocs_sched (void)
+{
+ return __get_nprocs ();
+}
+
/* On some architectures it is possible to distinguish between configured
and active cpus. */

208
glibc-rh1992702-2.patch Normal file
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@ -0,0 +1,208 @@
Patch proposed for upstream inclusion:
<https://sourceware.org/pipermail/libc-alpha/2021-September/130802.html>
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue Sep 7 09:22:58 2021 -0300
linux: Simplify get_nprocs
This patch simplifies the memory allocation code and uses the sched
routines instead of reimplement it. This still uses a stack
allocation buffer, so it can be used on malloc initialization code.
Linux currently supports at maximum of 4096 cpus for most architectures:
$ find -iname Kconfig | xargs git grep -A10 -w NR_CPUS | grep -w range
arch/alpha/Kconfig- range 2 32
arch/arc/Kconfig- range 2 4096
arch/arm/Kconfig- range 2 16 if DEBUG_KMAP_LOCAL
arch/arm/Kconfig- range 2 32 if !DEBUG_KMAP_LOCAL
arch/arm64/Kconfig- range 2 4096
arch/csky/Kconfig- range 2 32
arch/hexagon/Kconfig- range 2 6 if SMP
arch/ia64/Kconfig- range 2 4096
arch/mips/Kconfig- range 2 256
arch/openrisc/Kconfig- range 2 32
arch/parisc/Kconfig- range 2 32
arch/riscv/Kconfig- range 2 32
arch/s390/Kconfig- range 2 512
arch/sh/Kconfig- range 2 32
arch/sparc/Kconfig- range 2 32 if SPARC32
arch/sparc/Kconfig- range 2 4096 if SPARC64
arch/um/Kconfig- range 1 1
arch/x86/Kconfig-# [NR_CPUS_RANGE_BEGIN ... NR_CPUS_RANGE_END] range.
arch/x86/Kconfig- range NR_CPUS_RANGE_BEGIN NR_CPUS_RANGE_END
arch/xtensa/Kconfig- range 2 32
With x86 supporting 8192:
arch/x86/Kconfig
976 config NR_CPUS_RANGE_END
977 int
978 depends on X86_64
979 default 8192 if SMP && CPUMASK_OFFSTACK
980 default 512 if SMP && !CPUMASK_OFFSTACK
981 default 1 if !SMP
So using a maximum of 32k cpu should cover all cases (and I would
expect once we start to have many more CPUs that Linux would provide
a more straightforward way to query for such information).
A test is added to check if sched_getaffinity can successfully return
with large buffers.
Checked on x86_64-linux-gnu and i686-linux-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
diff --git a/posix/Makefile b/posix/Makefile
index a5229777eeb0e067..61fcdf015b4ec83b 100644
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -107,7 +107,8 @@ tests := test-errno tstgetopt testfnm runtests runptests \
tst-sysconf-empty-chroot tst-glob_symlinks tst-fexecve \
tst-glob-tilde test-ssize-max tst-spawn4 bug-regex37 \
bug-regex38 tst-regcomp-truncated tst-spawn-chdir \
- tst-wordexp-nocmd tst-execveat tst-spawn5
+ tst-wordexp-nocmd tst-execveat tst-spawn5 \
+ tst-sched_getaffinity
# Test for the glob symbol version that was replaced in glibc 2.27.
ifeq ($(have-GLIBC_2.26)$(build-shared),yesyes)
diff --git a/posix/tst-sched_getaffinity.c b/posix/tst-sched_getaffinity.c
new file mode 100644
index 0000000000000000..6d1fdcb05ff4d16c
--- /dev/null
+++ b/posix/tst-sched_getaffinity.c
@@ -0,0 +1,47 @@
+/* Tests for sched_getaffinity with large buffers.
+ Copyright (C) 2021 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <array_length.h>
+#include <sched.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+ /* The values are larger than the default cpu_set_t. */
+ const int bufsize[] = { 1<<11, 1<<12, 1<<13, 1<<14, 1<<15, 1<<16, 1<<17 };
+ int cpucount[array_length(bufsize)];
+
+ for (int i = 0; i < array_length (bufsize); i++)
+ {
+ cpu_set_t *cpuset = CPU_ALLOC (bufsize[i]);
+ TEST_VERIFY (cpuset != NULL);
+ size_t size = CPU_ALLOC_SIZE (bufsize[i]);
+ TEST_COMPARE (sched_getaffinity (0, size, cpuset), 0);
+ cpucount[i] = CPU_COUNT_S (size, cpuset);
+ CPU_FREE (cpuset);
+ }
+
+ for (int i = 0; i < array_length (cpucount) - 1; i++)
+ for (int j = 1; j < array_length (cpucount); j++)
+ TEST_COMPARE (cpucount[i], cpucount[j]);
+
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c
index e9c0dc4d83d4fb2a..1e3d88676df37f81 100644
--- a/sysdeps/unix/sysv/linux/getsysstats.c
+++ b/sysdeps/unix/sysv/linux/getsysstats.c
@@ -28,61 +28,29 @@
#include <sys/sysinfo.h>
#include <sysdep.h>
-/* Compute the population count of the entire array. */
-static int
-__get_nprocs_count (const unsigned long int *array, size_t length)
-{
- int count = 0;
- for (size_t i = 0; i < length; ++i)
- if (__builtin_add_overflow (count, __builtin_popcountl (array[i]),
- &count))
- return INT_MAX;
- return count;
-}
-
-/* __get_nprocs with a large buffer. */
-static int
-__get_nprocs_large (void)
-{
- /* This code cannot use scratch_buffer because it is used during
- malloc initialization. */
- size_t pagesize = GLRO (dl_pagesize);
- unsigned long int *page = __mmap (0, pagesize, PROT_READ | PROT_WRITE,
- MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
- if (page == MAP_FAILED)
- return 2;
- int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0, pagesize, page);
- int count;
- if (r > 0)
- count = __get_nprocs_count (page, pagesize / sizeof (unsigned long int));
- else if (r == -EINVAL)
- /* One page is still not enough to store the bits. A more-or-less
- arbitrary value. This assumes t hat such large systems never
- happen in practice. */
- count = GLRO (dl_pagesize) * CHAR_BIT;
- else
- count = 2;
- __munmap (page, GLRO (dl_pagesize));
- return count;
-}
-
int
__get_nprocs (void)
{
- /* Fast path for most systems. The kernel expects a buffer size
- that is a multiple of 8. */
- unsigned long int small_buffer[1024 / CHAR_BIT / sizeof (unsigned long int)];
- int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0,
- sizeof (small_buffer), small_buffer);
+ enum
+ {
+ max_num_cpus = 32768,
+ cpu_bits_size = CPU_ALLOC_SIZE (32768)
+ };
+
+ /* This cannot use malloc because it is used on malloc initialization. */
+ __cpu_mask cpu_bits[cpu_bits_size / sizeof (__cpu_mask)];
+ int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0, cpu_bits_size,
+ cpu_bits);
if (r > 0)
- return __get_nprocs_count (small_buffer, r / sizeof (unsigned long int));
+ return CPU_COUNT_S (cpu_bits_size, (cpu_set_t*) cpu_bits);
else if (r == -EINVAL)
- /* The kernel requests a larger buffer to store the data. */
- return __get_nprocs_large ();
- else
- /* Some other error. 2 is conservative (not a uniprocessor
- system, so atomics are needed). */
- return 2;
+ /* The input buffer is still not enough to store the number of cpus. This
+ is an arbitrary values assuming such systems should be rare and there
+ is no offline cpus. */
+ return max_num_cpus;
+ /* Some other error. 2 is conservative (not a uniprocessor system, so
+ atomics are needed). */
+ return 2;
}
libc_hidden_def (__get_nprocs)
weak_alias (__get_nprocs, get_nprocs)

202
glibc-rh1992702-3.patch Normal file
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@ -0,0 +1,202 @@
Patch proposed for upstream inclusion:
<https://sourceware.org/pipermail/libc-alpha/2021-September/130803.html>
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue Sep 7 09:22:59 2021 -0300
linux: Revert the use of sched_getaffinity on get_nproc (BZ #28310)
The use of sched_getaffinity on get_nproc and
sysconf (_SC_NPROCESSORS_ONLN) done in 903bc7dcc2acafc40 (BZ #27645)
breaks the top command in common hypervisor configurations and also
other monitoring tools.
The main issue using sched_getaffinity changed the symbols semantic
from system-wide scope of online CPUs to per-process one (which can
be changed with kernel cpusets or book parameters in VM).
This patch reverts mostly of the 903bc7dcc2acafc40, with the
exceptions:
* No more cached values and atomic updates, since they are inherent
racy.
* No /proc/cpuinfo fallback, since /proc/stat is already used and
it would require to revert more arch-specific code.
* The alloca is replace with a static buffer of 1024 bytes.
So the implementation first consult the sysfs, and fallbacks to procfs.
Checked on x86_64-linux-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c
index 1e3d88676df37f81..15ad91cf2f5905ac 100644
--- a/sysdeps/unix/sysv/linux/getsysstats.c
+++ b/sysdeps/unix/sysv/linux/getsysstats.c
@@ -17,6 +17,8 @@
<https://www.gnu.org/licenses/>. */
#include <array_length.h>
+#include <assert.h>
+#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <ldsodefs.h>
@@ -29,7 +31,7 @@
#include <sysdep.h>
int
-__get_nprocs (void)
+__get_nprocs_sched (void)
{
enum
{
@@ -52,14 +54,141 @@ __get_nprocs (void)
atomics are needed). */
return 2;
}
-libc_hidden_def (__get_nprocs)
-weak_alias (__get_nprocs, get_nprocs)
+
+static char *
+next_line (int fd, char *const buffer, char **cp, char **re,
+ char *const buffer_end)
+{
+ char *res = *cp;
+ char *nl = memchr (*cp, '\n', *re - *cp);
+ if (nl == NULL)
+ {
+ if (*cp != buffer)
+ {
+ if (*re == buffer_end)
+ {
+ memmove (buffer, *cp, *re - *cp);
+ *re = buffer + (*re - *cp);
+ *cp = buffer;
+
+ ssize_t n = __read_nocancel (fd, *re, buffer_end - *re);
+ if (n < 0)
+ return NULL;
+
+ *re += n;
+
+ nl = memchr (*cp, '\n', *re - *cp);
+ while (nl == NULL && *re == buffer_end)
+ {
+ /* Truncate too long lines. */
+ *re = buffer + 3 * (buffer_end - buffer) / 4;
+ n = __read_nocancel (fd, *re, buffer_end - *re);
+ if (n < 0)
+ return NULL;
+
+ nl = memchr (*re, '\n', n);
+ **re = '\n';
+ *re += n;
+ }
+ }
+ else
+ nl = memchr (*cp, '\n', *re - *cp);
+
+ res = *cp;
+ }
+
+ if (nl == NULL)
+ nl = *re - 1;
+ }
+
+ *cp = nl + 1;
+ assert (*cp <= *re);
+
+ return res == *re ? NULL : res;
+}
+
int
-__get_nprocs_sched (void)
+__get_nprocs (void)
{
- return __get_nprocs ();
+ enum { buffer_size = 1024 };
+ char buffer[buffer_size];
+ char *buffer_end = buffer + buffer_size;
+ char *cp = buffer_end;
+ char *re = buffer_end;
+
+ const int flags = O_RDONLY | O_CLOEXEC;
+ /* This file contains comma-separated ranges. */
+ int fd = __open_nocancel ("/sys/devices/system/cpu/online", flags);
+ char *l;
+ int result = 0;
+ if (fd != -1)
+ {
+ l = next_line (fd, buffer, &cp, &re, buffer_end);
+ if (l != NULL)
+ do
+ {
+ char *endp;
+ unsigned long int n = strtoul (l, &endp, 10);
+ if (l == endp)
+ {
+ result = 0;
+ break;
+ }
+
+ unsigned long int m = n;
+ if (*endp == '-')
+ {
+ l = endp + 1;
+ m = strtoul (l, &endp, 10);
+ if (l == endp)
+ {
+ result = 0;
+ break;
+ }
+ }
+
+ result += m - n + 1;
+
+ l = endp;
+ if (l < re && *l == ',')
+ ++l;
+ }
+ while (l < re && *l != '\n');
+
+ __close_nocancel_nostatus (fd);
+
+ if (result > 0)
+ return result;
+ }
+
+ cp = buffer_end;
+ re = buffer_end;
+
+ /* Default to an SMP system in case we cannot obtain an accurate
+ number. */
+ result = 2;
+
+ fd = __open_nocancel ("/proc/stat", flags);
+ if (fd != -1)
+ {
+ result = 0;
+
+ while ((l = next_line (fd, buffer, &cp, &re, buffer_end)) != NULL)
+ /* The current format of /proc/stat has all the cpu* entries
+ at the front. We assume here that stays this way. */
+ if (strncmp (l, "cpu", 3) != 0)
+ break;
+ else if (isdigit (l[3]))
+ ++result;
+
+ __close_nocancel_nostatus (fd);
+ }
+
+ return result;
}
+libc_hidden_def (__get_nprocs)
+weak_alias (__get_nprocs, get_nprocs)
/* On some architectures it is possible to distinguish between configured

8
glibc.spec
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@ -151,7 +151,7 @@ end \
Summary: The GNU libc libraries
Name: glibc
Version: %{glibcversion}
Release: 7%{?dist}
Release: 8%{?dist}
# In general, GPLv2+ is used by programs, LGPLv2+ is used for
# libraries.
@ -229,6 +229,9 @@ Patch23: glibc-python3.patch
Patch29: glibc-fedora-nsswitch.patch
Patch30: glibc-deprecated-selinux-makedb.patch
Patch31: glibc-deprecated-selinux-nscd.patch
Patch32: glibc-rh1992702-1.patch
Patch33: glibc-rh1992702-2.patch
Patch34: glibc-rh1992702-3.patch
##############################################################################
# Continued list of core "glibc" package information:
@ -2260,6 +2263,9 @@ fi
%files -f compat-libpthread-nonshared.filelist -n compat-libpthread-nonshared
%changelog
* Wed Sep 15 2021 Florian Weimer <fweimer@redhat.com> - 2.34.9000-8
- Use system CPU count for sysconf(_SC_NPROCESSORS_*) (#1992702)
* Wed Sep 15 2021 Florian Weimer <fweimer@redhat.com> - 2.34.9000-7
- Auto-sync with upstream branch master,
commit 2444ce5421c6036a503842d8dd8d93c27aad59ee: