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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 A1AEAC4363A for ; Mon, 26 Oct 2020 17:08:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A347206F7 for ; Mon, 26 Oct 2020 17:08:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="rHBnXExz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1787207AbgJZRIv (ORCPT ); Mon, 26 Oct 2020 13:08:51 -0400 Received: from z5.mailgun.us ([104.130.96.5]:17404 "EHLO z5.mailgun.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404185AbgJZRIt (ORCPT ); Mon, 26 Oct 2020 13:08:49 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1603732128; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=bGAwmL6gfMcp3WiAjsNWhDoMjBOZZo4qp5DW0lOE1kQ=; b=rHBnXExzXhciO7ueJK6b8YZ81wv6sHOPWWM450c59MQB28T0+BAztX8EfsSJoOwsHjQHICWJ w1Dso/teWeY9gKc4XB9IQ+76y3OtgM/84Lgkf/fR0jdeQ02CgHV1YiZI9xjO05JoZ4dmgWnN y2UUOgs/JyssKgkk8qaWOv8zxL0= X-Mailgun-Sending-Ip: 104.130.96.5 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n03.prod.us-west-2.postgun.com with SMTP id 5f9702a05c97867ace16d6c5 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Mon, 26 Oct 2020 17:08:48 GMT Sender: psodagud=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 6F74AC43387; Mon, 26 Oct 2020 17:08:48 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: psodagud) by smtp.codeaurora.org (Postfix) with ESMTPSA id CDF9AC433F0; Mon, 26 Oct 2020 17:08:47 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 26 Oct 2020 10:08:47 -0700 From: psodagud@codeaurora.org To: Thomas Gleixner Cc: Elliot Berman , Peter Zijlstra , "Paul E. McKenney" , Jonathan Corbet , Trilok Soni , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH] smp: Add bootcpus parameter to boot subset of CPUs In-Reply-To: <87v9f04n8r.fsf@nanos.tec.linutronix.de> References: <1603404243-5536-1-git-send-email-eberman@codeaurora.org> <87v9f04n8r.fsf@nanos.tec.linutronix.de> Message-ID: X-Sender: psodagud@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-10-23 14:59, Thomas Gleixner wrote: > On Thu, Oct 22 2020 at 15:04, Elliot Berman wrote: >> In a heterogeneous multiprocessor system, specifying the 'maxcpus' >> parameter on kernel command line does not provide sufficient control >> over which CPUs are brought online at kernel boot time, since CPUs may >> have nonuniform performance characteristics. Thus, add bootcpus kernel >> parameter to control which CPUs should be brought online during kernel >> boot. When both maxcpus and bootcpus is set, the more restrictive of >> the >> two are booted. > > What for? 'maxcpus' is a debug hack at best and outright dangerous on > certain architectures. Why do we need more of that? Just let the > machine > boot and offline the CPUs from user space. Hi Thomas and Peter, Based on my understanding with maxcpus option provides, maximum no of CPUs are brough up during the device boot up. There is a different case, in which we want to restrict which CPUs to be brough up. On a system with 8 cpus, if we set maxcpus as 3, cpu0, cpu1, and cpu2 are brough up during the bootup. For example, if we want to bring core0, core3 and core4 current maxcpu(as 3) setting would not help us. On some platform we want the flexibility on which CPUs to bring up during the device bootup. bootcpus command line is helping to bring specific CPUs and these patches are working downstream. > > Thanks, > > tglx