From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTP id 1D56A385782B for ; Mon, 13 Sep 2021 11:06:10 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 1D56A385782B Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-56-7aMlp-mUMsaP6zZNhmIPLA-1; Mon, 13 Sep 2021 07:05:59 -0400 X-MC-Unique: 7aMlp-mUMsaP6zZNhmIPLA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DD16836307; Mon, 13 Sep 2021 11:05:58 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.195.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C30515C3E0; Mon, 13 Sep 2021 11:05:57 +0000 (UTC) From: Florian Weimer To: Adhemerval Zanella Cc: libc-alpha@sourceware.org, Nicolas Saenz Julienne Subject: Re: [PATCH v2 3/3] linux: Revert the use of sched_getaffinity on get_nproc (BZ #28310) References: <20210907122259.79800-1-adhemerval.zanella@linaro.org> <20210907122259.79800-4-adhemerval.zanella@linaro.org> Date: Mon, 13 Sep 2021 13:05:55 +0200 In-Reply-To: <20210907122259.79800-4-adhemerval.zanella@linaro.org> (Adhemerval Zanella's message of "Tue, 7 Sep 2021 09:22:59 -0300") Message-ID: <87o88wd9bg.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, 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-List-Received-Date: Mon, 13 Sep 2021 11:06:11 -0000 * Adhemerval Zanella: > The use of sched_getaffinity on get_nproc and > sysconf (_SC_NPROCESSORS_ONLN) done in 903bc7dcc2acafc40 (BZ #27645) > breaks the top command in common hypervisor configurations and also > other monitoring tools. > > The main issue using sched_getaffinity changed the symbols semantic > from system-wide scope of online CPUs to per-process one (which can > be changed with kernel cpusets or book parameters in VM). > > This patch reverts mostly of the 903bc7dcc2acafc40, with the > exceptions: > > * No more cached values and atomic updates, since they are inherent > racy. > > * No /proc/cpuinfo fallback, since /proc/stat is already used and > it would require to revert more arch-specific code. > > * The alloca is replace with a static buffer of 1024 bytes. > > So the implementation first consult the sysfs, and fallbacks to procfs. Looks okay. Reviewed-by: Florian Weimer Thanks, Florian