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>
This commit is contained in:
Adhemerval Zanella
parent
11a02b035b
commit
33099d72e4
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@ -107,7 +107,8 @@ tests := test-errno tstgetopt testfnm runtests runptests \
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tst-sysconf-empty-chroot tst-glob_symlinks tst-fexecve \
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tst-glob-tilde test-ssize-max tst-spawn4 bug-regex37 \
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bug-regex38 tst-regcomp-truncated tst-spawn-chdir \
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tst-wordexp-nocmd tst-execveat tst-spawn5
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tst-wordexp-nocmd tst-execveat tst-spawn5 \
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tst-sched_getaffinity
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# Test for the glob symbol version that was replaced in glibc 2.27.
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ifeq ($(have-GLIBC_2.26)$(build-shared),yesyes)
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@ -0,0 +1,48 @@
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/* Tests for sched_getaffinity with large buffers.
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Copyright (C) 2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <array_length.h>
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#include <sched.h>
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#include <support/check.h>
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/* NB: this test may fail on system with more than 32k cpus. */
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static int
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do_test (void)
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{
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/* The values are larger than the default cpu_set_t. */
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const int bufsize[] = { 1<<11, 1<<12, 1<<13, 1<<14, 1<<15, 1<<16, 1<<17 };
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int cpucount[array_length (bufsize)];
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for (int i = 0; i < array_length (bufsize); i++)
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{
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cpu_set_t *cpuset = CPU_ALLOC (bufsize[i]);
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TEST_VERIFY (cpuset != NULL);
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size_t size = CPU_ALLOC_SIZE (bufsize[i]);
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TEST_COMPARE (sched_getaffinity (0, size, cpuset), 0);
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cpucount[i] = CPU_COUNT_S (size, cpuset);
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CPU_FREE (cpuset);
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}
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for (int i = 0; i < array_length (cpucount) - 1; i++)
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TEST_COMPARE (cpucount[i], cpucount[i + 1]);
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return 0;
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}
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#include <support/test-driver.c>
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@ -28,61 +28,29 @@
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#include <sys/sysinfo.h>
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#include <sysdep.h>
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/* Compute the population count of the entire array. */
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static int
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__get_nprocs_count (const unsigned long int *array, size_t length)
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{
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int count = 0;
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for (size_t i = 0; i < length; ++i)
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if (__builtin_add_overflow (count, __builtin_popcountl (array[i]),
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&count))
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return INT_MAX;
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return count;
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}
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/* __get_nprocs with a large buffer. */
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static int
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__get_nprocs_large (void)
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{
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/* This code cannot use scratch_buffer because it is used during
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malloc initialization. */
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size_t pagesize = GLRO (dl_pagesize);
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unsigned long int *page = __mmap (0, pagesize, PROT_READ | PROT_WRITE,
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MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
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if (page == MAP_FAILED)
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return 2;
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int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0, pagesize, page);
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int count;
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if (r > 0)
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count = __get_nprocs_count (page, pagesize / sizeof (unsigned long int));
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else if (r == -EINVAL)
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/* One page is still not enough to store the bits. A more-or-less
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arbitrary value. This assumes t hat such large systems never
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happen in practice. */
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count = GLRO (dl_pagesize) * CHAR_BIT;
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else
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count = 2;
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__munmap (page, GLRO (dl_pagesize));
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return count;
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}
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int
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__get_nprocs (void)
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{
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/* Fast path for most systems. The kernel expects a buffer size
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that is a multiple of 8. */
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unsigned long int small_buffer[1024 / CHAR_BIT / sizeof (unsigned long int)];
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int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0,
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sizeof (small_buffer), small_buffer);
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enum
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{
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max_num_cpus = 32768,
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cpu_bits_size = CPU_ALLOC_SIZE (32768)
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};
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/* This cannot use malloc because it is used on malloc initialization. */
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__cpu_mask cpu_bits[cpu_bits_size / sizeof (__cpu_mask)];
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int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0, cpu_bits_size,
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cpu_bits);
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if (r > 0)
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return __get_nprocs_count (small_buffer, r / sizeof (unsigned long int));
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return CPU_COUNT_S (cpu_bits_size, (cpu_set_t*) cpu_bits);
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else if (r == -EINVAL)
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/* The kernel requests a larger buffer to store the data. */
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return __get_nprocs_large ();
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else
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/* Some other error. 2 is conservative (not a uniprocessor
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system, so atomics are needed). */
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return 2;
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/* The input buffer is still not enough to store the number of cpus. This
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is an arbitrary values assuming such systems should be rare and there
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is no offline cpus. */
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return max_num_cpus;
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/* Some other error. 2 is conservative (not a uniprocessor system, so
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atomics are needed). */
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return 2;
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}
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libc_hidden_def (__get_nprocs)
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weak_alias (__get_nprocs, get_nprocs)
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