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=-5.3 required=3.0 tests=BAYES_00, 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 9CC38C433B4 for ; Wed, 21 Apr 2021 12:51:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 676986144C for ; Wed, 21 Apr 2021 12:51:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239976AbhDUMw3 (ORCPT ); Wed, 21 Apr 2021 08:52:29 -0400 Received: from elvis.franken.de ([193.175.24.41]:35165 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239950AbhDUMw2 (ORCPT ); Wed, 21 Apr 2021 08:52:28 -0400 Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1lZCKf-0004Cw-02; Wed, 21 Apr 2021 14:51:53 +0200 Received: by alpha.franken.de (Postfix, from userid 1000) id AA7E0C0840; Wed, 21 Apr 2021 14:01:48 +0200 (CEST) Date: Wed, 21 Apr 2021 14:01:48 +0200 From: Thomas Bogendoerfer To: "Maciej W. Rozycki" Cc: Arnd Bergmann , Huacai Chen , Huacai Chen , Jiaxun Yang , linux-arch@vger.kernel.org, linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/4] Reinstate and improve MIPS `do_div' implementation Message-ID: <20210421120148.GC8637@alpha.franken.de> References: 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) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Tue, Apr 20, 2021 at 04:50:22AM +0200, Maciej W. Rozycki wrote: > Hi, > > As Huacai has recently discovered the MIPS backend for `do_div' has been > broken and inadvertently disabled with commit c21004cd5b4c ("MIPS: Rewrite > to work with gcc 4.4.0."). As it is code I have originally > written myself and Huacai had issues bringing it back to life leading to a > request to discard it even I have decided to step in. > > In the end I have fixed the code and measured its performance to be ~100% > better on average than our generic code. I have decided it would be worth > having the test module I have prepared for correctness evaluation as well > as benchmarking, so I have included it with the series, also so that I can > refer to the results easily. > > In the end I have included four patches on this occasion: 1/4 is the test > module, 2/4 is an inline documentation fix/clarification for the `do_div' > wrapper, 3/4 enables the MIPS `__div64_32' backend and 4/4 adds a small > performance improvement to it. > > I have investigated a fifth change as a potential improvement where I > replaced the call to `do_div64_32' with a DIVU instruction for cases where > the high part of the intermediate divident is zero, but it has turned out > to regress performance a little, so I have discarded it. > > Also a follow-up change might be worth having to reduce the code size and > place `__div64_32' out of line for CC_OPTIMIZE_FOR_SIZE configurations, > but I have not fully prepared such a change at this time. I did use the > WIP form I have for performance evaluation however; see the figures quoted > with 4/4. > > These changes have been verified with a DECstation system with an R3400 > MIPS I processor @40MHz and a MTI Malta system with a 5Kc MIPS64 processor > @160MHz. > > See individual change descriptions and any additional discussions for > further details. > > Questions, comments or concerns? Otherwise please apply. series applied to mips-next. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]