From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/14023 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: sysconf(_SC_NPROCESSORS_CONF) returns the wrong value Date: Tue, 26 Mar 2019 18:45:41 +0100 Message-ID: <20190326174540.GH26605@port70.net> References: <20190315210202.GD6994@joraj-alpa> <20190316022534.GN26605@port70.net> <20190326162334.GF17481@joraj-alpa> Reply-To: musl@lists.openwall.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="34289"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mutt/1.10.1 (2018-07-13) Cc: Michael Jeanson , Richard Purdie , Mathieu Desnoyers , Jonathan Rajotte-Julien To: musl@lists.openwall.com Original-X-From: musl-return-14039-gllmg-musl=m.gmane.org@lists.openwall.com Tue Mar 26 18:45:57 2019 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.89) (envelope-from ) id 1h8q96-0008if-O6 for gllmg-musl@m.gmane.org; Tue, 26 Mar 2019 18:45:56 +0100 Original-Received: (qmail 32033 invoked by uid 550); 26 Mar 2019 17:45:54 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 32015 invoked from network); 26 Mar 2019 17:45:54 -0000 Mail-Followup-To: musl@lists.openwall.com, Michael Jeanson , Richard Purdie , Mathieu Desnoyers , Jonathan Rajotte-Julien Content-Disposition: inline In-Reply-To: <20190326162334.GF17481@joraj-alpa> Xref: news.gmane.org gmane.linux.lib.musl.general:14023 Archived-At: * Jonathan Rajotte-Julien [2019-03-26 12:23:34 -0400]: > > i think we need to know why does a process care if musl returns > > the wrong number? or what are the valid uses of such a number? > > (there are heterogeous systems like arm big-little, numa systems > > with many sockets, containers, virtualization,.. how deep may a > > user process need to go down in this rabbit hole?) > > Does the answers from Mathieu Desnoyers [1] and Florian Weimer [2] fit the bill? yes > > [1] https://www.openwall.com/lists/musl/2019/03/16/3 > [2] https://www.openwall.com/lists/musl/2019/03/19/1 > > > > note that most of /sys/devices/system/cpu/* is documented under > > Documentation/ABI/testing in linux, not in Documentation/ABI/stable > > and the format is not detailed, and some apis (e.g. /proc/cpuinfo) > > are known to be different on android (and grsec?) kernels it may > > be unmounted during early boot or in chroots, so sysfs parsing is > > only done when really necessary. > > For what it's worth, uclibc and uclibc-ng seem to iterate over > /sys/devices/system/cpu/* and fallback on online calculation if necessary. > > https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/unistd/sysconf.c#n102 > > In the mean time, we implemented a fallback similar to this when we do not "know" > the libc used (since musl does not come with __musl__, I read the reasons why, > no need to discuss this). > > Not sure of the direction musl should take but I strongly believe that the > behaviour regarding _SC_NPROCESSORS_CONF is not the appropriate one. i agree that the current behaviour is not ideal, but iterating over /sys/devices/system/cpu/cpu* may not be correct either.. based on current linux api docs. i don't understand why is that number different from the cpu set in /sys/devices/system/cpu/possible it seems any upper bound on the number of cpus would be valid but it's not clear how to provide that guarantee.