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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, 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 70DCFC43381 for ; Fri, 8 Mar 2019 13:35:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E6402087C for ; Fri, 8 Mar 2019 13:35:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Gx6Zs3x3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726638AbfCHNfV (ORCPT ); Fri, 8 Mar 2019 08:35:21 -0500 Received: from merlin.infradead.org ([205.233.59.134]:33854 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726432AbfCHNfV (ORCPT ); Fri, 8 Mar 2019 08:35:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=00hfKE/E7QSgNB45zu00ghT8eHguIg5JcE19KbrZHX0=; b=Gx6Zs3x3YclE4n0E/Is3VYTNm1 qF2U6hT3ZnMr71i68fBosTUuf28B3LYdPe/bYwVQe3X6oRCeYOxjCAJi4xmK1JY78mxY1dkMuyPsW fhOGt2WOBAjAPcxbxcA0rXTGf+8axqjzH8O8A7DSqdz/1MutSvtW18EWt8ByugACyEy1We5gHvFuA K775NweKbkwae7Sj6KbcNqF8u3MSuIfAe93tyWy+5OKxyMXoVWL1359y8v3BEF6hD1TlFOV1PXXBe BsaC+TQSTF4Elxszeay18Hj8B1999U3VCZ2rGFB29j0WkcYB1h5boiLu1Wbg14mRONQQSsizcHeFb 63maahPA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1h2Feb-0007Ip-D1; Fri, 08 Mar 2019 13:35:13 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6AF8120298BA7; Fri, 8 Mar 2019 14:35:10 +0100 (CET) Date: Fri, 8 Mar 2019 14:35:10 +0100 From: Peter Zijlstra To: Linus Torvalds Cc: Nadav Amit , Ingo Molnar , Borislav Petkov , Thomas Gleixner , Andrew Lutomirski , Linux List Kernel Mailing , Matthew Wilcox Subject: Re: [PATCH 1/5] x86/percpu: Differentiate this_cpu_{}() and __this_cpu_{}() Message-ID: <20190308133510.GX32494@hirez.programming.kicks-ass.net> References: <20190227101252.413192716@infradead.org> <20190227101544.210748832@infradead.org> <06F1CFAA-DD80-4DA7-A97C-E57814149CC4@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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, Feb 27, 2019 at 11:41:31AM -0800, Linus Torvalds wrote: > On Wed, Feb 27, 2019 at 9:57 AM Nadav Amit wrote: > > > > I’ll have a look at some specific function assembly, but overall, the “+m” > > approach might prevent even more code optimizations than the “volatile” one. > > Ok, that being the case, let's forget that patch. > > I still wonder about the added volatiles to the xadd/cmpxchg cases, > which already had the "memory" clobber which should make the volatile > immaterial.. That was mostly me being OCD style consistent; but also notice that the atomic ops also often have volatile even though they have a memory clobber.