From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from vmicros1.altlinux.org (vmicros1.altlinux.org [194.107.17.57]) by sourceware.org (Postfix) with ESMTP id 936053858412 for ; Sat, 5 Feb 2022 21:24:03 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 936053858412 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=altlinux.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=altlinux.org Received: from mua.local.altlinux.org (mua.local.altlinux.org [192.168.1.14]) by vmicros1.altlinux.org (Postfix) with ESMTP id 7BCA172C905 for ; Sun, 6 Feb 2022 00:24:02 +0300 (MSK) Received: by mua.local.altlinux.org (Postfix, from userid 508) id 6AAA97CD35B; Sun, 6 Feb 2022 00:24:02 +0300 (MSK) Date: Sun, 6 Feb 2022 00:24:02 +0300 From: "Dmitry V. Levin" To: libc-alpha@sourceware.org Subject: [PATCH] linux: fix accuracy of get_nprocs and get_nprocs_conf [BZ #28865] Message-ID: <20220205212402.GA5233@altlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-12.5 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE 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-List-Received-Date: Sat, 05 Feb 2022 21:24:05 -0000 get_nprocs() and get_nprocs_conf() use various methods to obtain an accurate number of processors. Re-introduce __get_nprocs_sched() as a source of information, and fix the order in which these methods are used to return the most accurate information. The primary source of information used in both functions remains unchanged. This also changes __get_nprocs_sched() error return value from 2 to 0, but all its users are already prepared to handle that. Old behavior: get_nprocs: /sys/devices/system/cpu/online -> /proc/stat -> 2 get_nprocs_conf: /sys/devices/system/cpu/ -> /proc/stat -> 2 New behavior: get_nprocs: /sys/devices/system/cpu/online -> sched_getaffinity -> /proc/stat -> 2 get_nprocs_conf: /sys/devices/system/cpu/ -> /proc/stat -> sched_getaffinity -> 2 Fixes: 342298278e ("linux: Revert the use of sched_getaffinity on get_nproc") Closes: BZ #28865 --- sysdeps/unix/sysv/linux/getsysstats.c | 101 ++++++++++++++++++-------- 1 file changed, 70 insertions(+), 31 deletions(-) diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c index c98c8ce3d4..e1ed96070c 100644 --- a/sysdeps/unix/sysv/linux/getsysstats.c +++ b/sysdeps/unix/sysv/linux/getsysstats.c @@ -50,9 +50,8 @@ __get_nprocs_sched (void) 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; + /* Some other error. */ + return 0; } static char * @@ -108,22 +107,19 @@ next_line (int fd, char *const buffer, char **cp, char **re, } static int -get_nproc_stat (char *buffer, size_t buffer_size) +get_nproc_stat (void) { + enum { buffer_size = 1024 }; + char buffer[buffer_size]; char *buffer_end = buffer + buffer_size; char *cp = buffer_end; char *re = buffer_end; - - /* Default to an SMP system in case we cannot obtain an accurate - number. */ - int result = 2; + int result = 0; const int flags = O_RDONLY | O_CLOEXEC; int fd = __open_nocancel ("/proc/stat", flags); if (fd != -1) { - result = 0; - char *l; while ((l = next_line (fd, buffer, &cp, &re, buffer_end)) != NULL) /* The current format of /proc/stat has all the cpu* entries @@ -139,8 +135,8 @@ get_nproc_stat (char *buffer, size_t buffer_size) return result; } -int -__get_nprocs (void) +static int +get_nprocs_cpu_online (void) { enum { buffer_size = 1024 }; char buffer[buffer_size]; @@ -179,7 +175,8 @@ __get_nprocs (void) } } - result += m - n + 1; + if (m >= n) + result += m - n + 1; l = endp; if (l < re && *l == ',') @@ -188,28 +185,18 @@ __get_nprocs (void) while (l < re && *l != '\n'); __close_nocancel_nostatus (fd); - - if (result > 0) - return result; } - return get_nproc_stat (buffer, buffer_size); + return result; } -libc_hidden_def (__get_nprocs) -weak_alias (__get_nprocs, get_nprocs) - -/* On some architectures it is possible to distinguish between configured - and active cpus. */ -int -__get_nprocs_conf (void) +static int +get_nprocs_cpu (void) { - /* Try to use the sysfs filesystem. It has actual information about - online processors. */ + int count = 0; DIR *dir = __opendir ("/sys/devices/system/cpu"); if (dir != NULL) { - int count = 0; struct dirent64 *d; while ((d = __readdir64 (dir)) != NULL) @@ -224,12 +211,64 @@ __get_nprocs_conf (void) __closedir (dir); - return count; } + return count; +} - enum { buffer_size = 1024 }; - char buffer[buffer_size]; - return get_nproc_stat (buffer, buffer_size); +int +__get_nprocs (void) +{ + int result; + + /* Try /sys/devices/system/cpu/online first. */ + result = get_nprocs_cpu_online (); + if (result) + return result; + + /* Try sched_getaffinity(2). */ + result = __get_nprocs_sched (); + if (result) + return result; + + /* Try /proc/stat. */ + result = get_nproc_stat (); + if (result) + return result; + + /* We failed to obtain an accurate number. Be conservative: return + the smallest number meaning that this is not a uniprocessor system, + so atomics are needed. */ + return 2; +} +libc_hidden_def (__get_nprocs) +weak_alias (__get_nprocs, get_nprocs) + +/* On some architectures it is possible to distinguish between configured + and active cpus. */ +int +__get_nprocs_conf (void) +{ + int result; + + /* Try /sys/devices/system/cpu/ first. */ + result = get_nprocs_cpu (); + if (result) + return result; + + /* Try /proc/stat. */ + result = get_nproc_stat (); + if (result) + return result; + + /* Try sched_getaffinity(2). */ + result = __get_nprocs_sched (); + if (result) + return result; + + /* We failed to obtain an accurate number. Be conservative: return + the smallest number meaning that this is not a uniprocessor system, + so atomics are needed. */ + return 2; } libc_hidden_def (__get_nprocs_conf) weak_alias (__get_nprocs_conf, get_nprocs_conf) -- ldv