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([177.194.59.218]) by smtp.gmail.com with ESMTPSA id f31sm21661848pgm.1.2021.07.13.07.26.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Jul 2021 07:26:35 -0700 (PDT) To: libc-alpha@sourceware.org Subject: [PATCH] linux: Simplify get_nprocs Date: Tue, 13 Jul 2021 11:26:32 -0300 Message-Id: <20210713142632.2813759-1-adhemerval.zanella@linaro.org> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-Spam-Status: No, score=-12.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Adhemerval Zanella via Libc-alpha From: Adhemerval Zanella Netto Reply-To: Adhemerval Zanella Cc: Florian Weimer Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" 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). Checked on x86_64-linux-gnu and i686-linux-gnu. --- sysdeps/unix/sysv/linux/getsysstats.c | 64 ++++++--------------------- 1 file changed, 14 insertions(+), 50 deletions(-) diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c index 1391e360b8..e752b0a111 100644 --- a/sysdeps/unix/sysv/linux/getsysstats.c +++ b/sysdeps/unix/sysv/linux/getsysstats.c @@ -29,61 +29,25 @@ #include #include -/* 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); + /* This cannot use malloc because it is used on malloc initialization. */ + enum { max_num_cpus = 32768 }; + size_t cpu_bits_size = CPU_ALLOC_SIZE (max_num_cpus); + __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)