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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 16158C5517A for ; Fri, 23 Oct 2020 21:59:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FA0C2137B for ; Fri, 23 Oct 2020 21:59:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="FpQmBJoq"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="nHmm/QYq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757036AbgJWV7v (ORCPT ); Fri, 23 Oct 2020 17:59:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757027AbgJWV7u (ORCPT ); Fri, 23 Oct 2020 17:59:50 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 591B8C0613CE; Fri, 23 Oct 2020 14:59:50 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1603490388; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=mcqtPkA0tz7ylkWcpgHi1whok+ruukbSXl7bVbRNeHw=; b=FpQmBJoq1nNNC4QO/xEsdNA1Wbti7sa5bKvyG9sxwcqPPWtOcPaCfWHtjhhrHtdUsbWyXk WuJFdPY9XA7e+0DEWHd8Rf+IBNRbxbf0fGtk3WY35MEYWRsCO/al04Qy+n8N35/YhhZLyT +qyXEDBepFoJ/UzLTB1z9KkOc67HKEEspRF1UkSXJFofyra8sQxfXRyr6iIdIJ522WMsTn rGHA9pvAWa0xtjYG5RpmS4+VYuClBkA7FcnnuaQjQsQavxrmtjMX1yyL73Onjqp8lR1m3x uqEwc+8Y5+pRUNn7WDf5/n76QQ5uM03H/QHZiUgjVoT9Lqy3Ug2xR58HjkD51A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1603490388; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=mcqtPkA0tz7ylkWcpgHi1whok+ruukbSXl7bVbRNeHw=; b=nHmm/QYqpi4s8doFzwGapHfMVQpfgwSLj29GjpCVLTMZfVMcMdPOuaBxwzoLga1IiapECr VsJQfTGT65LC3sCw== To: Elliot Berman , Peter Zijlstra , "Paul E. McKenney" , Jonathan Corbet Cc: Elliot Berman , Trilok Soni , Prasad Sodagudi , 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: <1603404243-5536-1-git-send-email-eberman@codeaurora.org> References: <1603404243-5536-1-git-send-email-eberman@codeaurora.org> Date: Fri, 23 Oct 2020 23:59:48 +0200 Message-ID: <87v9f04n8r.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks, tglx