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 4F22EC67871 for ; Thu, 27 Oct 2022 06:28:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231706AbiJ0G2B (ORCPT ); Thu, 27 Oct 2022 02:28:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbiJ0G17 (ORCPT ); Thu, 27 Oct 2022 02:27:59 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 64732C068B; Wed, 26 Oct 2022 23:27:57 -0700 (PDT) Received: from dggpemm500022.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4MybHc01XXzpW51; Thu, 27 Oct 2022 14:24:28 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500022.china.huawei.com (7.185.36.162) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Thu, 27 Oct 2022 14:27:54 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Thu, 27 Oct 2022 14:27:53 +0800 Subject: Re: [PATCH v7 00/11] kallsyms: Optimizes the performance of lookup symbols From: "Leizhen (ThunderTown)" To: Luis Chamberlain CC: Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Joe Lawrence , , , Masahiro Yamada , Alexei Starovoitov , Jiri Olsa , Kees Cook , Andrew Morton , , Steven Rostedt , "Ingo Molnar" References: <20221017064950.2038-1-thunder.leizhen@huawei.com> <77f1c8f0-5e67-0e57-9285-15ba613044fb@huawei.com> <4f06547b-456f-e1ec-c535-16577f502ff1@huawei.com> Message-ID: Date: Thu, 27 Oct 2022 14:27:53 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <4f06547b-456f-e1ec-c535-16577f502ff1@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 2022/10/27 11:26, Leizhen (ThunderTown) wrote: > > > On 2022/10/27 3:03, Luis Chamberlain wrote: >> On Wed, Oct 26, 2022 at 02:44:36PM +0800, Leizhen (ThunderTown) wrote: >>> On 2022/10/26 1:53, Luis Chamberlain wrote: >>>> This answers how we don't use a hash table, the question was *should* we >>>> use one? >>> >>> I'm not the original author, and I can only answer now based on my understanding. Maybe >>> the original author didn't think of the hash method, or he has weighed it out. >>> >>> Hash is a good solution if only performance is required and memory overhead is not >>> considered. Using hash will increase the memory size by up to "4 * kallsyms_num_syms + >>> 4 * ARRAY_SIZE(hashtable)" bytes, kallsyms_num_syms is about 1-2 million. Sorry, 1-2 million ==> 0.1~0.2 million >>> >>> Because I don't know what hash algorithm will be used, the cost of generating the >>> hash value corresponding to the symbol name is unknown now. But I think it's gonna >>> be small. But it definitely needs a simpler algorithm, the tool needs to implement >>> the same hash algorithm. >> >> For instance, you can look at evaluating if alloc_large_system_hash() would help. > > OK, I found the right hash function. In this way, the tool does not need to consider > the byte order. https://en.wikipedia.org/wiki/Jenkins_hash_function Let's go with jenkins_one_at_a_time_hash(), which looks simpler and doesn't even have to think about sizeof(long). It seems to be closest to our current needs. uint32_t jenkins_one_at_a_time_hash(const uint8_t* key, size_t length) { size_t i = 0; uint32_t hash = 0; while (i != length) { hash += key[i++]; hash += hash << 10; hash ^= hash >> 6; } hash += hash << 3; hash ^= hash >> 11; hash += hash << 15; return hash; } > > include/linux/stringhash.h > > /* > * Version 1: one byte at a time. Example of use: > * > * unsigned long hash = init_name_hash; > * while (*p) > * hash = partial_name_hash(tolower(*p++), hash); > * hash = end_name_hash(hash); > > >> >> Luis >> . >> > -- Regards, Zhen Lei