From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54E50C43464 for ; Thu, 17 Sep 2020 21:55:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 130C42083B for ; Thu, 17 Sep 2020 21:55:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725886AbgIQVzm (ORCPT ); Thu, 17 Sep 2020 17:55:42 -0400 Received: from mga01.intel.com ([192.55.52.88]:12370 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725858AbgIQVzm (ORCPT ); Thu, 17 Sep 2020 17:55:42 -0400 X-Greylist: delayed 426 seconds by postgrey-1.27 at vger.kernel.org; Thu, 17 Sep 2020 17:55:42 EDT IronPort-SDR: jRxvhOvAyKFRAKG4POtDmJZdbOLKFpHngnI7FqFkPfUn3kFsdbC0Z0MAlG9ag/+OESqNF0MtWk MseN3o52Roqw== X-IronPort-AV: E=McAfee;i="6000,8403,9747"; a="177899243" X-IronPort-AV: E=Sophos;i="5.77,272,1596524400"; d="scan'208";a="177899243" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Sep 2020 14:48:34 -0700 IronPort-SDR: DX1pqr/rasoGJGjKeGOdu7eMEy4RC3SvbgMQmyF6vW6QUwgqGohfhguGYmPQ9DQ5WmkoPalbwy QVgicDjCtLXA== X-IronPort-AV: E=Sophos;i="5.77,272,1596524400"; d="scan'208";a="483919158" Received: from jekeller-mobl1.amr.corp.intel.com (HELO [10.212.151.155]) ([10.212.151.155]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Sep 2020 14:48:33 -0700 Subject: Re: [RFC][Patch v1 1/3] sched/isolation: API to get num of hosekeeping CPUs To: Bjorn Helgaas , Nitesh Narayan Lal Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-pci@vger.kernel.org, frederic@kernel.org, mtosatti@redhat.com, sassmann@redhat.com, jeffrey.t.kirsher@intel.com, jlelli@redhat.com, hch@infradead.org, bhelgaas@google.com, mike.marciniszyn@intel.com, dennis.dalessandro@intel.com, thomas.lendacky@amd.com, jerinj@marvell.com, mathias.nyman@intel.com, jiri@nvidia.com, Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot References: <20200917201123.GA1726926@bjorn-Precision-5520> From: Jacob Keller Organization: Intel Corporation Message-ID: <238f4d32-ac26-e0c6-b53c-9f7ab98050ca@intel.com> Date: Thu, 17 Sep 2020 14:48:30 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.2.2 MIME-Version: 1.0 In-Reply-To: <20200917201123.GA1726926@bjorn-Precision-5520> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 9/17/2020 1:11 PM, Bjorn Helgaas wrote: > [+cc Ingo, Peter, Juri, Vincent (scheduler maintainers)] > > s/hosekeeping/housekeeping/ (in subject) > > On Wed, Sep 09, 2020 at 11:08:16AM -0400, Nitesh Narayan Lal wrote: >> Introduce a new API num_housekeeping_cpus(), that can be used to retrieve >> the number of housekeeping CPUs by reading an atomic variable >> __num_housekeeping_cpus. This variable is set from housekeeping_setup(). >> >> This API is introduced for the purpose of drivers that were previously >> relying only on num_online_cpus() to determine the number of MSIX vectors >> to create. In an RT environment with large isolated but a fewer >> housekeeping CPUs this was leading to a situation where an attempt to >> move all of the vectors corresponding to isolated CPUs to housekeeping >> CPUs was failing due to per CPU vector limit. > > Totally kibitzing here, but AFAICT the concepts of "isolated CPU" and > "housekeeping CPU" are not currently exposed to drivers, and it's not > completely clear to me that they should be. > > We have carefully constructed notions of possible, present, online, > active CPUs, and it seems like whatever we do here should be > somehow integrated with those. > Perhaps "active" CPUs could be separated to not include the isolated CPUs?