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=-5.8 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,URIBL_BLOCKED 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 3D657C433E9 for ; Wed, 10 Mar 2021 14:25:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0798364FFB for ; Wed, 10 Mar 2021 14:25:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233042AbhCJOZO (ORCPT ); Wed, 10 Mar 2021 09:25:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232746AbhCJOY5 (ORCPT ); Wed, 10 Mar 2021 09:24:57 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 98149C061760 for ; Wed, 10 Mar 2021 06:24:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=plOvh9vyCxI+W79dsawsRUqmt5nDXxIS3jse/b6xlb8=; b=P12Z1QOJ7Ys0pmztT9aYj3qM0T eeGReMBtFtdOaTIWJHIpmZN7wBuQ4L9uY02X4f9WZXO9WBMn1gsfEgg8qD0G0kgxBtF5LvLGu3C1I JTtMQdQB3zqjSyrsXkHZcn2pDrSpsqInvZ3l+iaJrpz7NmjXN9BBvT0BPMY3fTBn8PFtOpqFXYCbq AndpkJ/1F1qJ+sFNPrYod4TgJSvtTheoWby1wR17zcZ17UI/kir8jrYGvaHMDmAlNOFi9WzDimASd 94EbYe/cni19rSsGrmHwKuQ0eTAvKQvlJ3kclzDVKGhtSkoIicjKswgpPNYuLhpXoDMCVco5XNJnd NUnbbLBg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lJzlY-003gZB-F1; Wed, 10 Mar 2021 14:24:51 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4FB063011F0; Wed, 10 Mar 2021 15:24:47 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 43A9C21ADDC04; Wed, 10 Mar 2021 15:24:47 +0100 (CET) Date: Wed, 10 Mar 2021 15:24:47 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: The killing of ideal_nops[] Message-ID: References: <20210309120519.7c6bbb97@gandalf.local.home> <362BD2A4-016D-4F6B-8974-92C84DC0DDB4@zytor.com> <20210310091324.0c346d5f@oasis.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210310091324.0c346d5f@oasis.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 10, 2021 at 09:13:24AM -0500, Steven Rostedt wrote: > On Wed, 10 Mar 2021 11:22:48 +0100 > Peter Zijlstra wrote: > > > After this FEATURE_NOPL is unused except for required-features for > > x86_64. FEATURE_K8 is only used for PTI and FEATURE_K7 is unused. > > > > AFAICT this negatively affects lots of 32bit (DONTCARE) and 32bit on > > 64bit CPUs (CARELESS) and early AMD (K8) which is from 2003 and almost > > 2 decades old by now (SHRUG). > > > > Everything x86_64 since AMD K10 (2007) was using p6_nops. > > > > And per FEATURE_NOPL being required for x86_64, all those CPUs can use > > p6_nops. So stop caring about NOPs, simplify things and get on with life > > :-) > > Before ripping out all the ideal_nop logic, I wonder if we should just > force the nops you want now (that is, don't change the selected > ideal_nops, just "pretend" that the CPU wants p6_nops), and see if anyone > complains. After a few releases, if there's no complaints, then we can > rip out the ideal_nop logic. Nah, just rip the entire thing out. You should be happy about deterministic NOPs :-) NOP encoding is not something CPUs should differentiate on, that's just bollocks.