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,USER_AGENT_MUTT autolearn=unavailable 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 19FAFC43381 for ; Thu, 14 Feb 2019 10:31:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB8B4222A4 for ; Thu, 14 Feb 2019 10:31:54 +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="pzNAgZMF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393704AbfBNKbr (ORCPT ); Thu, 14 Feb 2019 05:31:47 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:60424 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388126AbfBNKbr (ORCPT ); Thu, 14 Feb 2019 05:31:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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: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=Cz5E1STMYTb9r24YsxFX2EIKYAjHOnBW1E39BRqOjIc=; b=pzNAgZMFQqf2rpZPA5AoHx2wY I21zX13gc0L3xvMCwenDvp1FgHFvAtk/Ttv98OAd9sHz/j7MHWTmbWD1IRuoL3gm9WurbolV5cejZ H6FRzhsPlyGQcAxHRF7dhdPR6BK09cMKIvoAl7ZbpE8qdulZxIzWDjfuSrrP7SCt17JALDEwo2sx9 vWoPBotEx9kAkYwutGqIuhxdOhtCKt2EY8p0IUKOuHiwPOBPtR1cijqdsY3iCmyAUwPbpnDPjLEXd gsgQHqF38bx5/cllVgVz6gKkdPDqy64vEJdqkrdG4af5a0WnT+G9t0xZxo3R8iuDrrrhb7ym39vb9 vciRDYdmw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1guEIw-0004W5-8o; Thu, 14 Feb 2019 10:31:42 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A63A820298375; Thu, 14 Feb 2019 11:31:40 +0100 (CET) Date: Thu, 14 Feb 2019 11:31:40 +0100 From: Peter Zijlstra To: Vineet Gupta Cc: David Laight , Alexey Brodkin , "linux-snps-arc@lists.infradead.org" , Arnd Bergmann , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , Mark Rutland Subject: Re: [PATCH] ARC: Explicitly set ARCH_SLAB_MINALIGN = 8 Message-ID: <20190214103140.GG32494@hirez.programming.kicks-ass.net> References: <20190208105519.26750-1-abrodkin@synopsys.com> <81017fe4-b31f-4942-e822-a7b70008b74d@synopsys.com> <20190213125651.GP32494@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Feb 13, 2019 at 03:23:36PM -0800, Vineet Gupta wrote: > On 2/13/19 4:56 AM, Peter Zijlstra wrote: > > > > Personally I think u64 and company should already force natural > > alignment; but alas. > > But there is an ISA/ABI angle here too. e.g. On 32-bit ARC, LDD (load double) is > allowed to take a 32-bit aligned address to load a register pair. Thus all u64 > need not be 64-bit aligned (unless attribute aligned 8 etc) hence the relaxation > in ABI (alignment of long long is 4). You could certainly argue that we end up > undoing some of it anyways by defining things like ARCH_KMALLOC_MINALIGN to 8, but > still... So what happens if the data is then split across two cachelines; will a STD vs LDD still be single-copy-atomic? I don't _think_ we rely on that for > sizeof(unsigned long), with the obvious exception of atomic64_t, but yuck... So even though it is allowed by the chip; does it really make sense to use this?