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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 059C0C432C0 for ; Thu, 21 Nov 2019 10:37:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1F972088F for ; Thu, 21 Nov 2019 10:37:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="Lxe4g4Wv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726716AbfKUKhl (ORCPT ); Thu, 21 Nov 2019 05:37:41 -0500 Received: from mail.skyhub.de ([5.9.137.197]:40430 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726293AbfKUKhk (ORCPT ); Thu, 21 Nov 2019 05:37:40 -0500 Received: from zn.tnic (p200300EC2F0F07006553A4184595DC73.dip0.t-ipconnect.de [IPv6:2003:ec:2f0f:700:6553:a418:4595:dc73]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 56EAC1EC0CE8; Thu, 21 Nov 2019 11:37:39 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1574332659; 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: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=my9hQkLlPxW1AW3Gf6LZ+XTRjwwqHQaGN1kMFbCEOqE=; b=Lxe4g4WvUvDvhj0e3y9i6X8rFEb/ZwgPwWLV+22CCGmthpcg/8F/AGemWTGZt97D+ZJisu TMqjdV8iM/oD7CTpIkXqMARMwe9RztOmT93qV8yoK1AXPakLeaa+VWzXLDzvnkz0KQNuR5 kbkg6ZBgj+DmK0a7/3FeZqgyjFAlQaY= Date: Thu, 21 Nov 2019 11:37:32 +0100 From: Borislav Petkov To: Dan Williams Cc: Thomas Gleixner , "Luck, Tony" , Dave Jiang , dmaengine@vger.kernel.org, Linux Kernel Mailing List , Vinod Koul , Jing Lin , "Raj, Ashok" , "Kumar, Sanjay K" , "Dey, Megha" , "Pan, Jacob jun" , "Liu, Yi L" , Jens Axboe , Andrew Morton , Ingo Molnar , Fenghua Yu , "H. Peter Anvin" Subject: Re: [PATCH RFC 01/14] x86/asm: add iosubmit_cmds512() based on movdir64b CPU instruction Message-ID: <20191121103732.GA6540@zn.tnic> References: <157428480574.36836.14057238306923901253.stgit@djiang5-desk3.ch.intel.com> <157428502934.36836.8119026517510193201.stgit@djiang5-desk3.ch.intel.com> <20191120215338.GN2634@zn.tnic> <20191120231923.GA32680@agluck-desk2.amr.corp.intel.com> <20191120232645.GO2634@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 20, 2019 at 05:32:51PM -0800, Dan Williams wrote: > True, but that would be a driver coding mistake flagged by the > WARN_ON_ONCE, and the failure is static. The driver must check for > static_cpu_has(X86_FEATURE_MOVDIR64B) once at init, So if you do that at driver init time, you don't need the static variant - simply use boot_cpu_has(). But if this function is going to be used on other platforms, then you need the check in the function and it must be static_cpu_has() for speed. The static_cpu_has() thing is a soft-of once check anyway because it gets patched by alternatives and after that it is 0 overhead. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette