From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.1 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS, T_BULK_RE_SUSP_NTLD,T_FROM_SUSPICIOUS_NTLD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 81D921F45F for ; Wed, 8 May 2019 23:04:38 +0000 (UTC) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-type; q=dns; s=default; b=Dr7S 82Fjbb4/fOwOQ8qhRV0qldTZ28OhIfOW2VBgKcsP0fgNK3aC9+EddZzU5eJvxMBI gkPJ4U2TTBDbbhcy888Lux+c8j7x1oHe3mpNWQMyLTExd2D4doq+akD2YNimIaDm opAVxXyetElaBGRLMRoNNwE9EPqQ7VbTSMKgynU= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-type; s=default; bh=IQ0s8DSg8c Wtd0V6i2E6mJ1+pQ4=; b=Bi5i1vEkaP4fIqwwVg/3eoFWDYj0i33CyY1hY+3YyQ f5mXvES/7j8UOedCAPWkYIqj66re5QHPqW7pZglX4ZNmPtAxqQ0bsDRHIwnHULmD AKNYWDPG35G1N6lA+su7M10smZnEyWGo/cU783n8LBzDwlOTOm2bt31K0/0yP5Nx 0= Received: (qmail 79725 invoked by alias); 8 May 2019 23:04:29 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 79655 invoked by uid 89); 8 May 2019 23:04:28 -0000 Authentication-Results: sourceware.org; auth=none X-HELO: git.icu MIME-Version: 1.0 References: <20190505203438.28140-1-shawn@git.icu> <20190506203210.8536-1-shawn@git.icu> In-Reply-To: From: Shawn Landden Date: Wed, 8 May 2019 18:04:11 -0500 Message-ID: Subject: Re: [PATCH] powerpc: add libmvec implementations of log and logf To: Joseph Myers Cc: libc-alpha@sourceware.org Content-Type: text/plain; charset="UTF-8" On Tue, May 7, 2019 at 10:21 AM Joseph Myers wrote: > > On Mon, 6 May 2019, Shawn Landden wrote: > > > When fed numbers in the range of 0 to 2^32-1 (as doubles) the vector log > > is about 75% faster than scalar log. > > Since you and Bert Tenjy have now posted rival patch versions implementing > vector log, a key performance comparison would be against the version > posted by Bert Tenjy > - and in > general, you should compare and contrast the two versions of log to > justify why one might be better than another. It's also important in such > cases to be very clear about where exactly the patch you are posting fits > into exactly what other patch series. > When I first looked at Bert's patch I saw all the scalar code for the special path and thought it wasn't a real vector implementation. Otherwise I wouldn't have tried to compete with him. HOWEVER, once I fixed the bugs in my benchmark programs, there is no performance advantage of doing either log or logf with vector operation, at least on this power 9 VPS---either mine or Bert's patches. I think this is because they require too many table lookups for the constants, and Power ISA 3.0 lacks both a gather instruction, and a permutexvar instruction, both of which could be used to vectorize these table lookups. (shufflevector can't do it) > -- > Joseph S. Myers > joseph@codesourcery.com