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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A9F05C43334 for ; Wed, 13 Jul 2022 09:58:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234765AbiGMJ6N (ORCPT ); Wed, 13 Jul 2022 05:58:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51720 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230398AbiGMJ54 (ORCPT ); Wed, 13 Jul 2022 05:57:56 -0400 Received: from mail-lf1-x132.google.com (mail-lf1-x132.google.com [IPv6:2a00:1450:4864:20::132]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8D3A4F90CB for ; Wed, 13 Jul 2022 02:57:55 -0700 (PDT) Received: by mail-lf1-x132.google.com with SMTP id o7so18192970lfq.9 for ; Wed, 13 Jul 2022 02:57:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=5yJHhqVPk2ZS/u5R/efMYnn4/6Ff7LLWCXjWXuOmA44=; b=KIdTsJJgOB+9snLwV677m/c3z4hhqQIkaFBF4oO6Xla3+z7OP3eSW062s/19GsAeyC HbxoIuT8Kl3Dz0UtJ6QTpITKSJ0qFKXazj4ZnJSz8j8xfqVC1oI/ArDFAxcUzi+aLXxL S/1S13TCOM6CVxxbgekoYa467td9h0u8IeaMxG1+4LtnqSLOsBojiC2accWglubsOPq7 x31AWRgVoMettp3rH58vNkHWi+vG2vMGttZ02lGj5SeljvVFhUIesq9shjpfjGTLUJOu 78SnhapNIoPadruEXeclkxywmrYDnbBLJMS0ASL1qSm3vBF3a1ugcuB6Wb1XXoFv67NK 2rfw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=5yJHhqVPk2ZS/u5R/efMYnn4/6Ff7LLWCXjWXuOmA44=; b=2r0Py10q3LTx12Ftz9AUBAN4Qz0GCjUn6nW0DypUukT4MHdmV+LdU294ts+Y+4XVx9 ZGxuEfm0x9FKuaG+PCwEmsGJsA30WiycKIonzAYQ0VBtlcTeEs3qcoelWj0NGJ3qI5w0 EzLgqxaZ4kLB9xngv7EF2jrE0rzfwcrk7wlHEfbDLk9RxaE5y2WZk90CTvlktaGf76rR o63mCCIbvz5qJ2lf3OhckBzOPcrBN5COdXx+yFy4Be96IhR5y3orFq84kDZn2QOsZtY3 LAgBQdQcIlMZx1X8TyaTrQ+6z0P1VSJlJRGeDywQSTE3kFiJmG2m8DACXrKchOsIYTaD 0C6Q== X-Gm-Message-State: AJIora/zxABK3+4f1Bht7jdB4plzVoHHcJNI4NsTrvlPHREvVuRkj48J AZ2zOJZTQZndN2/BxOw4aZA= X-Google-Smtp-Source: AGRyM1uHmrRyQOgBw36xgx7SvFrGhNZGwduPjYLZtzRtCrL8NLSzjnWpX3S8N5Lp+O46NN2AwEPpKQ== X-Received: by 2002:a05:6512:1295:b0:481:1a61:8d21 with SMTP id u21-20020a056512129500b004811a618d21mr1455205lfs.500.1657706273830; Wed, 13 Jul 2022 02:57:53 -0700 (PDT) Received: from [192.168.1.2] (broadband-188-32-106-30.ip.moscow.rt.ru. [188.32.106.30]) by smtp.gmail.com with ESMTPSA id q16-20020a2eb4b0000000b002559299b0e7sm3032200ljm.86.2022.07.13.02.57.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Jul 2022 02:57:53 -0700 (PDT) Message-ID: Date: Wed, 13 Jul 2022 12:57:52 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH 2/2] lib/string.c: Optimize memchr() Content-Language: en-US To: David Laight , 'Yu-Jen Chang' Cc: "andy@kernel.org" , "akinobu.mita@gmail.com" , Ching-Chun Huang , "linux-kernel@vger.kernel.org" References: <20220710142822.52539-1-arthurchang09@gmail.com> <20220710142822.52539-3-arthurchang09@gmail.com> <3a1b50d2-a7aa-3e89-56fe-5d14ef9da22f@gmail.com> <48db247e-f6fd-cb4b-7cc5-455bf26bb153@gmail.com> <49a8be9269ee47de9fc2d0d7f09eb0b1@AcuMS.aculab.com> From: Andrey Semashev In-Reply-To: <49a8be9269ee47de9fc2d0d7f09eb0b1@AcuMS.aculab.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/13/22 12:39, David Laight wrote: > From: Yu-Jen Chang >> Sent: 12 July 2022 15:59 > ... >>> I think you're missing the point. Loads at unaligned addresses may not >>> be allowed by hardware using conventional load instructions or may be >>> inefficient. Given that this memchr implementation is used as a fallback >>> when no hardware-specific version is available, you should be >>> conservative wrt. hardware capabilities and behavior. You should >>> probably have a pre-alignment loop. >> >> Got it. I add pre-alignment loop. It aligns the address to 8 or 4bytes. > > That should be predicated on !HAS_EFFICIENT_UNALIGNED_ACCESS. If there is a pre-alignment loop, there won't be unaligned loads, so there shouldn't be the need for the HAS_EFFICIENT_UNALIGNED_ACCESS check. Unless I misunderstand what HAS_EFFICIENT_UNALIGNED_ACCESS indicates.