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=-5.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 47DA4C388F9 for ; Wed, 11 Nov 2020 16:07:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C4EDD206A1 for ; Wed, 11 Nov 2020 16:07:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="hVEz6/Ov" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726221AbgKKQHV (ORCPT ); Wed, 11 Nov 2020 11:07:21 -0500 Received: from m12-16.163.com ([220.181.12.16]:55203 "EHLO m12-16.163.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725933AbgKKQHV (ORCPT ); Wed, 11 Nov 2020 11:07:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=Subject:From:Message-ID:Date:MIME-Version; bh=W5cWG wWXk3nu7LBSIHt95Byo2DTsGA15qcB3rBxTqAY=; b=hVEz6/OvnpobokAG24p5A DNBz45fP07BQcKuYAJULxBkzCfo+L7ZFx/C4sKVOEDwcFmc//OyZehpwJXzBACoP zIYHk7Q7j1ZCLTA1MN20q7D0vv8Q0Izd1L7Dl2+CNzEG6eL/On1Lsmvg62X2AccP C1OYAEYSofuInhxaQ0K5fU= Received: from [192.168.0.102] (unknown [120.229.59.128]) by smtp12 (Coremail) with SMTP id EMCowABnTGHyC6xf27IxLQ--.51829S3; Thu, 12 Nov 2020 00:06:14 +0800 (CST) Subject: Re: [PATCH 2/3] lib: zlib_inflate: improves decompression performance To: Jann Horn Cc: Andrew Morton , kernel list , Zhaoxiu Zeng References: <20201109191601.14053-1-zengzhaoxiu@163.com> <20201109192508.14186-1-zengzhaoxiu@163.com> From: Zhaoxiu Zeng Message-ID: <2442c8fb-ff36-41ce-9349-d162639d5c3b@163.com> Date: Thu, 12 Nov 2020 00:06:09 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-CM-TRANSID: EMCowABnTGHyC6xf27IxLQ--.51829S3 X-Coremail-Antispam: 1Uf129KBjvdXoW7Wr4DWr13ZFy5Xr45uF4kJFb_yoW3XwcEyw n5WFyqka1UCwnrGF4UCr4S9r1xGF4UuFs2qw4aka9xX34fZrs8WFWDKr93tFy5Ga129F18 Zw15ur45K39xtjkaLaAFLSUrUUUUUb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUvcSsGvfC2KfnxnUUI43ZEXa7IU0PfHUUUUUU== X-Originating-IP: [120.229.59.128] X-CM-SenderInfo: p2hqw6xkdr5xrx6rljoofrz/xtbByhfZgF0COtEQrwABsO Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2020/11/11 11:46, Jann Horn 写道: > On Mon, Nov 9, 2020 at 8:27 PM wrote: >> This patch does: >> 1. Cleanup code and reduce branches >> 2. Use copy_from_back to copy the matched bytes from the back output buffer > > What exactly is copy_from_back()? Is it like memmove()? If yes, have > you tried using memmove() instead of the code added in patch 1/3? > If use memcpy(or memmove), the code will be like this: while (dist < len) { memcpy(out, out - dist, dist); out += dist; len -= dist; } memcpy(out, out - dist, len); or: const u8 * const from = out - dist; while (dist < len) { memcpy(out, from, dist); out += dist; len -= dist; dist *= 2; } memcpy(out, from, len); In addition, the len is small in most cases, so the function calls are expensive.