From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 17346 invoked from network); 6 Jul 2021 09:00:40 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 6 Jul 2021 09:00:40 -0000 Received: (qmail 17807 invoked by uid 550); 6 Jul 2021 09:00:36 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 17788 invoked from network); 6 Jul 2021 09:00:35 -0000 Date: Tue, 6 Jul 2021 10:00:20 +0100 From: Vincent Donnefort To: jyknight@google.com, musl@lists.openwall.com Message-ID: <20210706090020.GB216826@e120877-lin.cambridge.arm.com> References: <20210702132937.GA239501@e120877-lin.cambridge.arm.com> <20210703212018.GA3554268@port70.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210703212018.GA3554268@port70.net> User-Agent: Mutt/1.5.24 (2015-08-30) Subject: Re: [musl] Re: Re: [PATCH v2] sysconf: add _SC_NPROCESSORS_CONF support On Sat, Jul 03, 2021 at 11:20:18PM +0200, Szabolcs Nagy wrote: > * Vincent Donnefort [2021-07-02 14:29:37 +0100]: > > Here's a new thread as I never received your previous email and I just > > noticed the answer today. > > > > I'm not sure I understand why I can't use "present". As per the kernel > > documentation: > > > > possible: CPUs that have been allocated resources and can be > > brought online if they are present. [cpu_possible_mask] > > > > present: CPUs that have been identified as being present in the > > system. [cpu_present_mask] > > > > > > In this example, the NR_CPUS config option is 128, but the kernel was > > started with possible_cpus=144. There are 4 CPUs in the system and cpu2 > > was manually taken offline (and is the only CPU that can be brought > > online.):: > > > > kernel_max: 127 > > offline: 2,4-127,128-143 > > online: 0-1,3 > > possible: 0-127 > > present: 0-3 > > > > So indeed I could use "possible"... but there's a chance the two masks won't > > be equal, and the sysfs entries are matching "present", not "possible". > > > > "possible" is the CPUs that have allocated resources and can be physically > > added to the system. "present" is the CPUs that are known as physically > > present but might be offline. > > i guess we just need a guarantee that these interfaces are stable > and the set of present cpus don't change during the lifetime of a > process. (can that even work with checkpoint/restore? probably not > our problem) In that case "possible" is what we want. It can't change during the kernel lifetime, while "present" can. -- Vincent