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=-7.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS, T_DKIMWL_WL_HIGH,USER_AGENT_MUTT autolearn=ham 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 D1FCEC43219 for ; Sat, 4 May 2019 00:27:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 92D572081C for ; Sat, 4 May 2019 00:27:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556929659; bh=khpHJXJyePxHxqjcbb/bixCjMWGObu2ArDNoVY/Nty8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ymEbI8LH3oLZWgmRvLmwmhnM4ULaUCWOw7BL0OyRhn0Zz6vE//rwIbx6k9A//bbVm 8DMZezRIxh5LZ4EIcXS7csI3GmGnF1nSTXkzhWhEEval+2RYnw7KeRm8kWV3Tys70Z wEdVIbDPyGk+CBtHO6PM1KXohdNlZHNKH+UfYmt4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726580AbfEDA1i (ORCPT ); Fri, 3 May 2019 20:27:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:33394 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726059AbfEDA1i (ORCPT ); Fri, 3 May 2019 20:27:38 -0400 Received: from localhost (lfbn-1-18355-218.w90-101.abo.wanadoo.fr [90.101.143.218]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9D72B2075C; Sat, 4 May 2019 00:27:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556929657; bh=khpHJXJyePxHxqjcbb/bixCjMWGObu2ArDNoVY/Nty8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=z7XkEWV2vjJNbDEsLW0NtVXECUbk5ovIcZzmySxXPPA0c4XhSPF4oJf3uV6mVjE0B 4Oon05InP3j69i34Z8R8yBxK7L8ShAupRMHHD6eHKfcRmvDxgg7T2/7HFLya7kNIbh q4zjPm/bPUmyCoyNHQviV4YwhowaQfLBQWpbsbO0= Date: Sat, 4 May 2019 02:27:34 +0200 From: Frederic Weisbecker To: hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com, npiggin@gmail.com, fweisbec@gmail.com, peterz@infradead.org, torvalds@linux-foundation.org Cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:sched/core] sched/isolation: Require a present CPU in housekeeping mask Message-ID: <20190504002733.GB19076@lenoir> References: <20190411033448.20842-5-npiggin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 03, 2019 at 10:47:37AM -0700, tip-bot for Nicholas Piggin wrote: > Commit-ID: 9219565aa89033a9cfdae788c1940473a1253d6c > Gitweb: https://git.kernel.org/tip/9219565aa89033a9cfdae788c1940473a1253d6c > Author: Nicholas Piggin > AuthorDate: Thu, 11 Apr 2019 13:34:47 +1000 > Committer: Ingo Molnar > CommitDate: Fri, 3 May 2019 19:42:58 +0200 > > sched/isolation: Require a present CPU in housekeeping mask > > During housekeeping mask setup, currently a possible CPU is required. > That does not guarantee the CPU would be available at boot time, so > check to ensure that at least one present CPU is in the mask. I have a doubt about the requirements and semantics of cpu_present_mask. IIUC a present CPU means that it is physically plugged in (from ACPI perspective) but might not be logically plugged in (set on cpu_online_mask). But do we have the guarantee that a present CPU _will_ be online at least once right after the boot? After all, kernel parameters such as "maxcpus=" can prevent from turning some CPUs on. I guess there are even more creative ways to achieve that. In any case we really require the housekeeper to be forced online. Perhaps I missed that enforcement somewhere in the patchset? Thanks.