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 BAA02C54EBC for ; Thu, 5 Jan 2023 07:48:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229909AbjAEHsP (ORCPT ); Thu, 5 Jan 2023 02:48:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43964 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229519AbjAEHsN (ORCPT ); Thu, 5 Jan 2023 02:48:13 -0500 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 51A7F14028; Wed, 4 Jan 2023 23:48:11 -0800 (PST) Received: from dggpemm500006.china.huawei.com (unknown [172.30.72.53]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4Nndp96Sx0z16MVL; Thu, 5 Jan 2023 15:46:41 +0800 (CST) 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 15.1.2375.34; Thu, 5 Jan 2023 15:48:07 +0800 Subject: Re: [PATCH 2/3] bpf: Optimize get_modules_for_addrs() To: Petr Mladek CC: Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Joe Lawrence , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Steven Rostedt , Masami Hiramatsu , Mark Rutland , , , , , Luis Chamberlain , References: <20221230112729.351-1-thunder.leizhen@huawei.com> <20221230112729.351-3-thunder.leizhen@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: Date: Thu, 5 Jan 2023 15:48:07 +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: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2023/1/5 0:25, Petr Mladek wrote: > On Fri 2022-12-30 19:27:28, Zhen Lei wrote: >> Function __module_address() can quickly return the pointer of the module >> to which an address belongs. We do not need to traverse the symbols of all >> modules to check whether each address in addrs[] is the start address of >> the corresponding symbol, because register_fprobe_ips() will do this check >> later. >> >> Assuming that there are m modules, each module has n symbols on average, >> and the number of addresses 'addrs_cnt' is abbreviated as K. Then the time >> complexity of the original method is O(K * log(K)) + O(m * n * log(K)), >> and the time complexity of current method is O(K * (log(m) + M)), M <= m. >> (m * n * log(K)) / (K * m) ==> n / log2(K). Even if n is 10 and K is 128, >> the ratio is still greater than 1. Therefore, the new method will >> generally have better performance. >> >> Signed-off-by: Zhen Lei >> --- >> kernel/trace/bpf_trace.c | 101 ++++++++++++++++----------------------- >> 1 file changed, 40 insertions(+), 61 deletions(-) >> >> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c >> index 5f3be4bc16403a5..0ff9037098bd241 100644 >> --- a/kernel/trace/bpf_trace.c >> +++ b/kernel/trace/bpf_trace.c >> @@ -2684,69 +2684,55 @@ static void symbols_swap_r(void *a, void *b, int size, const void *priv) >> } >> } >> >> -struct module_addr_args { >> - unsigned long *addrs; >> - u32 addrs_cnt; >> - struct module **mods; >> - int mods_cnt; >> - int mods_cap; >> -}; >> - >> -static int module_callback(void *data, const char *name, >> - struct module *mod, unsigned long addr) >> +static int get_modules_for_addrs(struct module ***out_mods, unsigned long *addrs, u32 addrs_cnt) >> { >> - struct module_addr_args *args = data; >> - struct module **mods; >> - >> - /* We iterate all modules symbols and for each we: >> - * - search for it in provided addresses array >> - * - if found we check if we already have the module pointer stored >> - * (we iterate modules sequentially, so we can check just the last >> - * module pointer) >> - * - take module reference and store it >> - */ >> - if (!bsearch(&addr, args->addrs, args->addrs_cnt, sizeof(addr), >> - bpf_kprobe_multi_addrs_cmp)) >> - return 0; >> + int i, j, err; >> + int mods_cnt = 0; >> + int mods_cap = 0; >> + struct module *mod; >> + struct module **mods = NULL; >> >> - if (args->mods && args->mods[args->mods_cnt - 1] == mod) >> - return 0; >> + for (i = 0; i < addrs_cnt; i++) { >> + mod = __module_address(addrs[i]); > > This must be called under module_mutex to make sure that the module > would not disappear. > >> + if (!mod) >> + continue; >> >> - if (args->mods_cnt == args->mods_cap) { >> - args->mods_cap = max(16, args->mods_cap * 3 / 2); >> - mods = krealloc_array(args->mods, args->mods_cap, sizeof(*mods), GFP_KERNEL); >> - if (!mods) >> - return -ENOMEM; >> - args->mods = mods; >> - } >> + /* check if we already have the module pointer stored */ >> + for (j = 0; j < mods_cnt; j++) { >> + if (mods[j] == mod) >> + break; >> + } > > This might get optimized like the original code. > > My understanding is that the addresses are sorted in "addrs" array. > So, the address is either part of the last found module or it belongs > to a completely new module. I'm in a hurry to get to the airport now. I will reply next week. move_module() shows that a module has three layouts, and the memory area is discontinuous. I originally wanted to implement what you suggested below. I'll analyze it in depth next week. Maybe it'll work. > > for (i = 0; i < addrs_cnt; i++) { > /* > * The adresses are sorted. The adress either belongs > * to the last found module or a new one. > * > * This is safe because we already have reference > * on the found modules. > */ > if (mods_cnt && within_module(addrs[i], mods[mods_cnt - 1])) > continue; > > mutex_lock(&module_mutex); > mod = __module_address(addrs[i]); > if (mod && !try_module_get(mod)) { > mutex_unlock(&module_mutex); > goto failed; > } > mutex_unlock(&module_mutex); > > /* > * Nope when the address was not from a module. > * > * Is this correct? What if the module has gone in > * the meantime? Anyway, the original code > * worked this way. > * > * FIXME: I would personally make sure that it is part > * of vmlinux or so. > */ > if (!mod) > continue; > > /* store the module into mods array */ > ... > > > > >> + if (j < mods_cnt) >> + continue; >> >> - if (!try_module_get(mod)) >> - return -EINVAL; >> + if (mods_cnt == mods_cap) { >> + struct module **new_mods; >> >> - args->mods[args->mods_cnt] = mod; >> - args->mods_cnt++; >> - return 0; >> -} >> + mods_cap = max(16, mods_cap * 3 / 2); >> + new_mods = krealloc_array(mods, mods_cap, sizeof(*mods), GFP_KERNEL); >> + if (!new_mods) { >> + err = -ENOMEM; >> + goto failed; >> + } >> + mods = new_mods; >> + } >> >> -static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u32 addrs_cnt) >> -{ >> - struct module_addr_args args = { >> - .addrs = addrs, >> - .addrs_cnt = addrs_cnt, >> - }; >> - int err; >> + if (!try_module_get(mod)) { >> + err = -EINVAL; >> + goto failed; >> + } >> >> - /* We return either err < 0 in case of error, ... */ >> - err = module_kallsyms_on_each_symbol(NULL, module_callback, &args); >> - if (err) { >> - kprobe_multi_put_modules(args.mods, args.mods_cnt); >> - kfree(args.mods); >> - return err; >> + mods[mods_cnt] = mod; >> + mods_cnt++; >> } >> >> - /* or number of modules found if everything is ok. */ >> - *mods = args.mods; >> - return args.mods_cnt; >> + *out_mods = mods; >> + return mods_cnt; >> + >> +failed: >> + kprobe_multi_put_modules(mods, mods_cnt); >> + kfree(mods); >> + return err; >> } >> >> int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) > > Otherwise, it looks good. IMHO, the new code looks more straightforward > than the original one. > > Best Regards, > Petr > . > -- Regards, Zhen Lei