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=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 0EB48C433DF for ; Fri, 5 Jun 2020 23:47:50 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 95F24206E6 for ; Fri, 5 Jun 2020 23:47:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 95F24206E6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49dzpp1rRNzDr2s for ; Sat, 6 Jun 2020 09:47:46 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=permerror (SPF Permanent Error: Unknown mechanism found: ip:192.40.192.88/32) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lists.ozlabs.org (Postfix) with ESMTP id 49dzmW2b0nzDr0Q for ; Sat, 6 Jun 2020 09:45:45 +1000 (AEST) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 055NjQXo031764; Fri, 5 Jun 2020 18:45:26 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 055NjNbh031763; Fri, 5 Jun 2020 18:45:23 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 5 Jun 2020 18:45:23 -0500 From: Segher Boessenkool To: Rich Felker Subject: Re: [musl] Re: ppc64le and 32-bit LE userland compatibility Message-ID: <20200605234523.GU31009@gate.crashing.org> References: <20200604171232.GG31009@gate.crashing.org> <20200604171844.GO1079@brightrain.aerifal.cx> <20200604173312.GI31009@gate.crashing.org> <20200604211009.GK31009@gate.crashing.org> <60fa8bd7-2439-4403-a0eb-166a2fb49a4b@www.fastmail.com> <20200604233516.GM31009@gate.crashing.org> <17459c98-3bd3-4a5d-a828-993b6deef44f@www.fastmail.com> <20200605172702.GP31009@gate.crashing.org> <20200605175045.GW1079@brightrain.aerifal.cx> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200605175045.GW1079@brightrain.aerifal.cx> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: libc-alpha@sourceware.org, eery@paperfox.es, Daniel Kolesa , musl@lists.openwall.com, Will Springer , Palmer Dabbelt via binutils , via libc-dev , Michal =?iso-8859-1?Q?Such=E1nek?= , linuxppc-dev@lists.ozlabs.org, Joseph Myers Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi! On Fri, Jun 05, 2020 at 01:50:46PM -0400, Rich Felker wrote: > On Fri, Jun 05, 2020 at 12:27:02PM -0500, Segher Boessenkool wrote: > > > I'm also not really all that convinced that vectors make a huge difference in non-specialized code (autovectorization still has a way to go) > > > > They do make a huge difference, depending on the application of course. > > But VSX is not just vectors even: it also gives you twice as many > > floating point scalars (64 now), and in newer versions of the ISA it can > > be beneficially used for integer scalars even. > > Vectorization is useful for a lot of things, and I'm sure there are > specialized workloads that benefit from 64 scalars, but I've never > encountered a place where having more than 16 registers made a > practical difference. 20 years ago 32 FP registers was already often a limitation, making FFT and similar kernels almost twice slower than they could otherwise be. Things are only *worse* with short vectors, not better. In general with floating point data you need more registers (because you have more state to look at concurrently) than with integer data. *Of course* having 64 floating point registers does not matter if your whole program only ever uses three floating point values, total, let alone concurrently. > The fact that there are specialized areas where this stuff matters > does not imply there aren't huge domains where it's completely > irrelevant. There are very few domains where ISA 2.07 does not have significant advantages over ISA 2.01. That is Power8 vs. Power4. > > No, that is exactly the point of requiring ISA 2.07. Anything can use > > ISA 2.07 (incl. VSX) without checking first, and without having a > > fallback to some other implementation. Going from ISA 2.01 to 2.07 is > > more than a decade of improvements, it is not trivial at all. > > This only affects code that's non-portable and PPC-specific, which a No, it does not. It is not only about vector registers, either. > I think a lot of the unnecessary fighting on this topic is arising > from differences of opinion over what an ABI entails. I would call > what you're talking about a "platform" and more of a platform-specific > *API* than an ABI -- it's about guarantees of interfaces available to > the programmer, not implementation details of linkage. No, this is very much about the ABI. The B stands for Binary. Which is what this is about. Segher