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=-9.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 07B38C433DF for ; Wed, 29 Jul 2020 20:44:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C603A206D4 for ; Wed, 29 Jul 2020 20:44:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1596055453; bh=qLclcthyaIVq9FHNhNz4KHXGIpoZhJNR9DipamyBoKA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=sFQKCjotSm/ZdbXkIOOnpBJKBfpPIuVI8d7ZNc07OJtRSxcfqZ9GCtoY65fQlzALW qRplFEp0NZ4Ydc1lUlxbseyF2LXKFh1k4af41hmEe2tYhBvBES4Px27BJ+zR49nAum eF4cjWC/q+zZrikkW5JdN+ABonCGgK2mBzO+rNrw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726962AbgG2UoM (ORCPT ); Wed, 29 Jul 2020 16:44:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:59844 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726496AbgG2UoM (ORCPT ); Wed, 29 Jul 2020 16:44:12 -0400 Received: from quaco.ghostprotocols.net (unknown [179.97.37.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D67B12068F; Wed, 29 Jul 2020 20:44:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1596055452; bh=qLclcthyaIVq9FHNhNz4KHXGIpoZhJNR9DipamyBoKA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=0g8GExDae9GS3BIIs6kvFVJgTAVyo+67M9muKbxaUqwvLHI9Tre4FMpm1NFb35TKR YMHzBO380YchTaVZtXt0Y+s2nysOI83rUzggkpTFQCHb6x8RtNXXGoMwluFsi7uJVT YDA+HE5ppQfwDSM2HjKdd3GxYTqW6ZPO1prAwg8c= Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 4546340E6B; Wed, 29 Jul 2020 17:44:09 -0300 (-03) Date: Wed, 29 Jul 2020 17:44:09 -0300 From: Arnaldo Carvalho de Melo To: Ian Rogers Cc: Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Thomas Gleixner , Andi Kleen , linux-kernel@vger.kernel.org, Stephane Eranian Subject: Re: [PATCH] perf bench: Add benchmark of find_next_bit Message-ID: <20200729204409.GF433799@kernel.org> References: <20200724071959.3110510-1-irogers@google.com> <20200728115152.GB3328@kernel.org> <20200729195918.GE433799@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200729195918.GE433799@kernel.org> X-Url: http://acmel.wordpress.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Wed, Jul 29, 2020 at 04:59:18PM -0300, Arnaldo Carvalho de Melo escreveu: > Em Tue, Jul 28, 2020 at 08:51:52AM -0300, Arnaldo Carvalho de Melo escreveu: > > Em Fri, Jul 24, 2020 at 12:19:59AM -0700, Ian Rogers escreveu: > > > for_each_set_bit, or similar functions like for_each_cpu, may be hot > > > within the kernel. If many bits were set then one could imagine on > > > Intel a "bt" instruction with every bit may be faster than the function > > > call and word length find_next_bit logic. Add a benchmark to measure > > > this. > > > > Thanks, applied. > > > This benchmark on AMD rome and Intel skylakex shows "bt" is not a good > > > option except for very small bitmaps. > > > > +++ b/tools/perf/bench/find-bit-bench.c > > > > +#if defined(__i386__) || defined(__x86_64__) > > > +static bool asm_test_bit(long nr, const unsigned long *addr) > > > +{ > > > + bool oldbit; > > > + > > > + asm volatile("bt %2,%1" > > > + : "=@ccc" (oldbit) > > > + : "m" (*(unsigned long *)addr), "Ir" (nr) : "memory"); > > > + > > > + return oldbit; > > Some old clang versions are not liking this: Failed with: clang version 3.8.0 (tags/RELEASE_380/final) clang version 3.8.1 (tags/RELEASE_381/final) clang version 4.0.0 (tags/RELEASE_400/final) Alpine clang version 8.0.0 (tags/RELEASE_800/final) (based on LLVM 8.0.0) Alpine clang version 5.0.0 (tags/RELEASE_500/final) (based on LLVM 5.0.0) Alpine clang version 5.0.1 (tags/RELEASE_501/final) (based on LLVM 5.0.1) Alpine clang version 5.0.1 (tags/RELEASE_502/final) (based on LLVM 5.0.1) Worked with: Alpine clang version 9.0.0 (https://git.alpinelinux.org/aports f7f0d2c2b8bcd6a5843401a9a702029556492689) (based on LLVM 9.0.0) Alpine clang version 10.0.0 (https://gitlab.alpinelinux.org/alpine/aports.git 7445adce501f8473efdb93b17b5eaf2f1445ed4c) Alpine clang version 10.0.0 (git://git.alpinelinux.org/aports 7445adce501f8473efdb93b17b5eaf2f1445ed4c) Also failed for; # grep FAIL dm.log/summary | grep -v alpine alt:p8: FAIL clang version 3.8.0 (tags/RELEASE_380/final) alt:p9: FAIL clang version 7.0.1 amazonlinux:1: FAIL clang version 3.6.2 (tags/RELEASE_362/final) amazonlinux:2: FAIL clang version 7.0.1 (Amazon Linux 2 7.0.1-1.amzn2.0.2) #