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 8320DFA3740 for ; Mon, 31 Oct 2022 04:56:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229475AbiJaE4I (ORCPT ); Mon, 31 Oct 2022 00:56:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229546AbiJaE4H (ORCPT ); Mon, 31 Oct 2022 00:56:07 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E6F35115D; Sun, 30 Oct 2022 21:56:03 -0700 (PDT) Received: from dggpemm500022.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4N112340HHzVjL5; Mon, 31 Oct 2022 12:51:07 +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; Mon, 31 Oct 2022 12:56:01 +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; Mon, 31 Oct 2022 12:56:01 +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> <712fae84-aadc-7d29-f311-a3352bab6346@huawei.com> Message-ID: Date: Mon, 31 Oct 2022 12:55:49 +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: <712fae84-aadc-7d29-f311-a3352bab6346@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: On 2022/10/29 16:10, Leizhen (ThunderTown) wrote: > > > On 2022/10/27 14:27, Leizhen (ThunderTown) wrote: >> >> >> 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. >>> > > The following three hash algorithms are compared. The kernel is compiled by defconfig > on arm64. > > |---------------------------------------------------------------------------------------| > | | hash &= HASH_TABLE_SIZE - 1 | > | | number of conflicts >= 1000 | > |---------------------------------------------------------------------------------------| > | ARRAY_SIZE(hash_table) | crc16 | jhash_one_at_a_time | string hash_32 | > |---------------------------------------------------------------------------------------| > | | 345b: 3905 | 0d40: 1013 | 4a4c: 6548 | > | | 35bb: 1016 | 35ce: 6549 | 883a: 1015 | > | 0x10000 | 385b: 6548 | 4440: 19126 | d05f: 19129 | > | | f0ba: 19127 | 7ebe: 3916 | ecda: 3903 | > |---------------------------------------------------------------------------------------| > | | 0ba: 19168 | 440: 19165 | 05f: 19170 | > | | 45b: 3955 | 5ce: 6577 | 83a: 1066 | > | 0x1000 | 5bb: 1069 | d40: 1052 | a4c: 6609 | > | | 85b: 6582 | ebe: 3938 | cda: 3924 | > |---------------------------------------------------------------------------------------| > > Based on the above test results, I conclude that: > 1. For the worst-case scenario, the three algorithms are not much different. But the kernel > only implements crc16 and string hash_32. The latter is not processed byte-by-byte, so > it is coupled with byte order and sizeof(long). So crc16 is the best choice. > 2. For the worst-case scenario, there are almost 19K strings are mapped to the same hash > value，just over 1/10 of the total. And with my current compression-then-comparison > approach, it's 25-30 times faster. So there's still a need for my current approach, and > they can be combined. > if (nr_conflicts(key) >= CONST_N) { > newname = compress(name); > for_each_name_in_slot(key): compare(new_name) > } else { > for_each_name_in_slot(key): compare(name) > } > > Above CONST_N can be roughly calculated: > time_of_compress(name) + N * time_of_compare(new_name) <= N * time_of_compare(name) > 3. For the worst-case scenario, there is no obvious difference between ARRAY_SIZE(hash_table) > 0x10000 and 0x1000. So ARRAY_SIZE(hash_table)=0x1000 is enough. > Statistic information: > |------------------------------------------------------| > | nr_conflicts(key) | ARRAY_SIZE(hash_table) | > |------------------------------------------------------| > | <= ? | 0x1000 | 0x10000 | > |------------------------------------------------------| > | 0 | 0 | 7821 | > | 20 | 19 | 57375 | > | 40 | 2419 | 124 | > | 60 | 1343 | 70 | > | 80 | 149 | 73 | > | 100 | 38 | 49 | > | 200 | 108 | 16 | > | 400 | 14 | 2 | > | 600 | 2 | 2 | > | 800 | 0 | 0 | > | 1000 | 0 | 0 | > | 100000 | 4 | 4 | > |------------------------------------------------------| > > > Also, I re-calculated: > Using hash will increase the memory size by up to "6 * kallsyms_num_syms + 4 * ARRAY_SIZE(hashtable)" > |---- What I said earlier was 4 > The increased size is close to 1 MB if CONFIG_KALLSYMS_ALL=y. > > Hi, Luis: > For the reasons of the above-mentioned second conclusion. And except for patches 4-6, > even if only the hash method is used, other patches and option "--lto-clang" in patch 6/11 > are also needed. If you don't mind, I'd like to use hash at the next stage. The current > patch set is already huge. I just had an update in response to David Laight's email. The hash solution is like a centrist. It doesn't seem very feasible. Now, we need to make a decision. Choose one of the two: 1. Continue with my current approach. Improve the average performance of kallsyms_lookup_name() by 20 to 30 times. The memory overhead is increased by: arm64 (defconfig): 73.5KiB and 4.0% if CONFIG_KALLSYMS_ALL=y. 19.8KiB and 2.8% if CONFIG_KALLSYMS_ALL=n. x86 (defconfig): 49.0KiB and 3.0% if CONFIG_KALLSYMS_ALL=y. 16.8KiB and 2.3% if CONFIG_KALLSYMS_ALL=n. 2. Sort names, binary search (The static function causes duplicate names. Additional work is required） 2^18=262144, only up to 18 symbol expansions and comparisons are required. The performance is definitely excellent, although I haven't tested it yet. The memory overhead is increased by: 6 * kallsyms_num_syms arm64 (defconfig): 1MiB if CONFIG_KALLSYMS_ALL=y. 362KiB if CONFIG_KALLSYMS_ALL=n. x86 (defconfig): 770KiB if CONFIG_KALLSYMS_ALL=y. 356KiB if CONFIG_KALLSYMS_ALL=n. > > >>> 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