From patchwork Wed Sep 30 04:27:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 11807839 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D1C07618 for ; Wed, 30 Sep 2020 04:28:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ACB712087D for ; Wed, 30 Sep 2020 04:28:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fb.com header.i=@fb.com header.b="mOSfltDe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725320AbgI3E2R (ORCPT ); Wed, 30 Sep 2020 00:28:17 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:26514 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725792AbgI3E2R (ORCPT ); Wed, 30 Sep 2020 00:28:17 -0400 Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 08U4Plgr003642 for ; Tue, 29 Sep 2020 21:28:15 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding : content-type; s=facebook; bh=jMWzajsOzYPyL+veJikMgTzCQD8avh8xXgYd/cqVjl0=; b=mOSfltDeceLEbnGJtJqQuwdLvcri6VLVgQUb2e0hnhreCgrUABlk4LyIIUm8qdgoMMRb bT3OpalYL1/oHt7sUf2WV4AvDH1naD2hx8vfQ1gV4RbnpNtqzstHrkmN1/kZ3NogCF2v xIvDxRdA5cSK6GLmhyib6WNCugKZlYXKDtY= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 33tn4tpgwx-2 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 29 Sep 2020 21:28:15 -0700 Received: from intmgw004.08.frc2.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:82::c) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Tue, 29 Sep 2020 21:28:13 -0700 Received: by devbig012.ftw2.facebook.com (Postfix, from userid 137359) id 618BA2EC77F1; Tue, 29 Sep 2020 21:28:09 -0700 (PDT) From: Andrii Nakryiko To: CC: , Andrii Nakryiko Subject: [PATCH dwarves 08/11] btf_encoder: revamp how per-CPU variables are encoded Date: Tue, 29 Sep 2020 21:27:39 -0700 Message-ID: <20200930042742.2525310-9-andriin@fb.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200930042742.2525310-1-andriin@fb.com> References: <20200930042742.2525310-1-andriin@fb.com> MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-30_01:2020-09-29,2020-09-30 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 adultscore=0 suspectscore=13 bulkscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 malwarescore=0 mlxscore=0 mlxlogscore=999 priorityscore=1501 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009300032 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Right now to encode per-CPU variables in BTF, pahole iterates complete vmlinux symbol table for each CU. There are 2500 CUs for a typical kernel image. Overall, to encode 287 per-CPU variables pahole spends more than 10% of its CPU budget, this is incredibly wasteful. This patch revamps how this is done. Now it pre-processes symbol table once before any of per-CU processing starts. It remembers each per-CPU variable symbol, including its address, size, and name. Then during processing each CU, binary search is used to correlate DWARF variable with per-CPU symbols and figure out if variable belongs to per-CPU data section. If the match is found, BTF_KIND_VAR is emitted and var_secinfo is recorded, just like before. At the very end, after all CUs are processed, BTF_KIND_DATASEC is emitted with sorted variables. This change makes per-CPU variables generation overhead pretty negligible and returns back about 10% of CPU usage. Performance counter stats for './pahole -J /home/andriin/linux-build/default/vmlinux': BEFORE: 19.160149000 seconds user 1.304873000 seconds sys 24,114.05 msec task-clock # 0.999 CPUs utilized 83 context-switches # 0.003 K/sec 0 cpu-migrations # 0.000 K/sec 622,417 page-faults # 0.026 M/sec 72,897,315,125 cycles # 3.023 GHz (25.02%) 127,807,316,959 instructions # 1.75 insn per cycle (25.01%) 29,087,179,117 branches # 1206.234 M/sec (25.01%) 464,105,921 branch-misses # 1.60% of all branches (25.01%) 30,252,119,368 L1-dcache-loads # 1254.543 M/sec (25.01%) 1,156,336,207 L1-dcache-load-misses # 3.82% of all L1-dcache hits (25.05%) 343,373,503 LLC-loads # 14.240 M/sec (25.02%) 12,044,977 LLC-load-misses # 3.51% of all LL-cache hits (25.01%) 24.136198321 seconds time elapsed 22.729693000 seconds user 1.384859000 seconds sys AFTER: 16.781455000 seconds user 1.343956000 seconds sys 23,398.77 msec task-clock # 1.000 CPUs utilized 86 context-switches # 0.004 K/sec 0 cpu-migrations # 0.000 K/sec 622,420 page-faults # 0.027 M/sec 68,395,641,468 cycles # 2.923 GHz (25.05%) 114,241,327,034 instructions # 1.67 insn per cycle (25.01%) 26,330,711,718 branches # 1125.303 M/sec (25.01%) 465,926,869 branch-misses # 1.77% of all branches (25.00%) 24,662,984,772 L1-dcache-loads # 1054.029 M/sec (25.00%) 1,054,052,064 L1-dcache-load-misses # 4.27% of all L1-dcache hits (25.00%) 340,970,622 LLC-loads # 14.572 M/sec (25.00%) 16,032,297 LLC-load-misses # 4.70% of all LL-cache hits (25.03%) 23.402259654 seconds time elapsed 21.916437000 seconds user 1.482826000 seconds sys Signed-off-by: Andrii Nakryiko --- btf_encoder.c | 239 +++++++++++++++++++++++++++++--------------------- libbtf.c | 6 +- libbtf.h | 1 + 3 files changed, 142 insertions(+), 104 deletions(-) diff --git a/btf_encoder.c b/btf_encoder.c index 91b68694bca5..a6be35b2daac 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -17,6 +17,7 @@ #include "btf_encoder.h" #include /* for isalpha() and isalnum() */ +#include /* for qsort() and bsearch() */ #include /* @@ -53,17 +54,17 @@ static bool btf_name_valid(const char *p) return !*p; } -static void dump_invalid_symbol(const char *msg, const char *sym, const char *cu, +static void dump_invalid_symbol(const char *msg, const char *sym, int verbose, bool force) { if (force) { if (verbose) - fprintf(stderr, "PAHOLE: Warning: %s, ignored (sym: '%s', cu: '%s').\n", - msg, sym, cu); + fprintf(stderr, "PAHOLE: Warning: %s, ignored (sym: '%s').\n", + msg, sym); return; } - fprintf(stderr, "PAHOLE: Error: %s (sym: '%s', cu: '%s').\n", msg, sym, cu); + fprintf(stderr, "PAHOLE: Error: %s (sym: '%s').\n", msg, sym); fprintf(stderr, "PAHOLE: Error: Use '-j' or '--force' to ignore such symbols and force emit the btf.\n"); } @@ -202,6 +203,9 @@ int btf_encoder__encode() { int err; + if (gobuffer__size(&btfe->percpu_secinfo) != 0) + btf_elf__add_datasec_type(btfe, PERCPU_SECTION, &btfe->percpu_secinfo); + err = btf_elf__encode(btfe, 0); btf_elf__delete(btfe); btfe = NULL; @@ -209,24 +213,117 @@ int btf_encoder__encode() return err; } -#define HASHADDR__BITS 8 -#define HASHADDR__SIZE (1UL << HASHADDR__BITS) -#define hashaddr__fn(key) hash_64(key, HASHADDR__BITS) +#define MAX_PERCPU_VAR_CNT 4096 + +struct var_info { + uint64_t addr; + uint32_t sz; + const char *name; +}; + +static struct var_info percpu_vars[MAX_PERCPU_VAR_CNT]; +static int percpu_var_cnt; + +static int percpu_var_cmp(const void *_a, const void *_b) +{ + const struct var_info *a = _a; + const struct var_info *b = _b; + + if (a->addr == b->addr) + return 0; + return a->addr < b->addr ? -1 : 1; +} + +static bool percpu_var_exists(uint64_t addr, uint32_t *sz, const char **name) +{ + const struct var_info *p; + struct var_info key = { .addr = addr }; + + p = bsearch(&key, percpu_vars, percpu_var_cnt, + sizeof(percpu_vars[0]), percpu_var_cmp); + + if (!p) + return false; + + *sz = p->sz; + *name = p->name; + return true; +} -static struct variable *hashaddr__find_variable(const struct hlist_head hashtable[], - const uint64_t addr) +static int find_all_percpu_vars(struct btf_elf *btfe) { - struct variable *variable; - struct hlist_node *pos; - uint16_t bucket = hashaddr__fn(addr); - const struct hlist_head *head = &hashtable[bucket]; - - hlist_for_each_entry(variable, pos, head, tool_hnode) { - if (variable->ip.addr == addr) - return variable; + uint32_t core_id; + GElf_Sym sym; + + /* cache variables' addresses, preparing for searching in symtab. */ + percpu_var_cnt = 0; + + /* search within symtab for percpu variables */ + elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) { + const char *sym_name; + uint64_t addr; + uint32_t size; + + /* compare a symbol's shndx to determine if it's a percpu variable */ + if (elf_sym__section(&sym) != btfe->percpu_shndx) + continue; + if (elf_sym__type(&sym) != STT_OBJECT) + continue; + + addr = elf_sym__value(&sym); + /* + * Store only those symbols that have allocated space in the percpu section. + * This excludes the following three types of symbols: + * + * 1. __ADDRESSABLE(sym), which are forcely emitted as symbols. + * 2. __UNIQUE_ID(prefix), which are introduced to generate unique ids. + * 3. __exitcall(fn), functions which are labeled as exit calls. + * + * In addition, the variables defined using DEFINE_PERCPU_FIRST are + * also not included, which currently includes: + * + * 1. fixed_percpu_data + */ + if (!addr) + continue; + + sym_name = elf_sym__name(&sym, btfe->symtab); + if (!btf_name_valid(sym_name)) { + dump_invalid_symbol("Found symbol of invalid name when encoding btf", + sym_name, btf_elf__verbose, btf_elf__force); + if (btf_elf__force) + continue; + return -1; + } + size = elf_sym__size(&sym); + if (!size) { + dump_invalid_symbol("Found symbol of zero size when encoding btf", + sym_name, btf_elf__verbose, btf_elf__force); + if (btf_elf__force) + continue; + return -1; + } + + if (btf_elf__verbose) + printf("Found per-CPU symbol '%s' at address 0x%lx\n", sym_name, addr); + + if (percpu_var_cnt == MAX_PERCPU_VAR_CNT) { + fprintf(stderr, "Reached the limit of per-CPU variables: %d\n", + MAX_PERCPU_VAR_CNT); + return -1; + } + percpu_vars[percpu_var_cnt].addr = addr; + percpu_vars[percpu_var_cnt].sz = size; + percpu_vars[percpu_var_cnt].name = sym_name; + percpu_var_cnt++; } - return NULL; + if (percpu_var_cnt) + qsort(percpu_vars, percpu_var_cnt, sizeof(percpu_vars[0]), percpu_var_cmp); + + if (btf_elf__verbose) + printf("Found %d per-CPU variables!\n", percpu_var_cnt); + return 0; } int cu__encode_btf(struct cu *cu, int verbose, bool force, @@ -234,13 +331,10 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, { uint32_t type_id_off; uint32_t core_id; + struct variable *var; struct function *fn; struct tag *pos; int err = 0; - struct hlist_head hash_addr[HASHADDR__SIZE]; - struct variable *var; - bool has_global_var = false; - GElf_Sym sym; if (btfe && strcmp(btfe->filename, cu->filename)) { err = btf_encoder__encode(); @@ -257,6 +351,9 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, if (!btfe) return -1; + if (!skip_encoding_vars && find_all_percpu_vars(btfe)) + goto out; + has_index_type = false; need_index_type = false; array_index_id = 0; @@ -278,6 +375,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, } btf_elf__verbose = verbose; + btf_elf__force = force; type_id_off = btf__get_nr_types(btfe->btf); cu__for_each_type(cu, core_id, pos) { @@ -325,12 +423,11 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, if (verbose) printf("search cu '%s' for percpu global variables.\n", cu->name); - /* cache variables' addresses, preparing for searching in symtab. */ - for (core_id = 0; core_id < HASHADDR__SIZE; ++core_id) - INIT_HLIST_HEAD(&hash_addr[core_id]); - cu__for_each_variable(cu, core_id, pos) { - struct hlist_head *head; + uint32_t size, type, linkage, offset; + const char *name; + uint64_t addr; + int id; var = tag__variable(pos); if (var->declaration) @@ -338,79 +435,24 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, /* percpu variables are allocated in global space */ if (variable__scope(var) != VSCOPE_GLOBAL) continue; - has_global_var = true; - head = &hash_addr[hashaddr__fn(var->ip.addr)]; - hlist_add_head(&var->tool_hnode, head); - } - if (!has_global_var) { - if (verbose) - printf("cu has no global variable defined, skip.\n"); - goto out; - } - - /* search within symtab for percpu variables */ - elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) { - uint32_t linkage, type, size, offset; - int32_t btf_var_id, btf_var_secinfo_id; - uint64_t addr; - const char *sym_name; - - /* compare a symbol's shndx to determine if it's a percpu variable */ - if (elf_sym__section(&sym) != btfe->percpu_shndx) - continue; - if (elf_sym__type(&sym) != STT_OBJECT) - continue; - addr = elf_sym__value(&sym); - /* - * Store only those symbols that have allocated space in the percpu section. - * This excludes the following three types of symbols: - * - * 1. __ADDRESSABLE(sym), which are forcely emitted as symbols. - * 2. __UNIQUE_ID(prefix), which are introduced to generate unique ids. - * 3. __exitcall(fn), functions which are labeled as exit calls. - * - * In addition, the variables defined using DEFINE_PERCPU_FIRST are - * also not included, which currently includes: - * - * 1. fixed_percpu_data - */ - if (!addr) - continue; - var = hashaddr__find_variable(hash_addr, addr); - if (var == NULL) - continue; - - sym_name = elf_sym__name(&sym, btfe->symtab); - if (!btf_name_valid(sym_name)) { - dump_invalid_symbol("Found symbol of invalid name when encoding btf", - sym_name, cu->name, verbose, force); - if (force) - continue; - err = -1; - break; - } type = var->ip.tag.type + type_id_off; - size = elf_sym__size(&sym); - if (!size) { - dump_invalid_symbol("Found symbol of zero size when encoding btf", - sym_name, cu->name, verbose, force); - if (force) - continue; - err = -1; - break; - } + addr = var->ip.addr; + linkage = var->external ? BTF_VAR_GLOBAL_ALLOCATED : BTF_VAR_STATIC; + if (!percpu_var_exists(addr, &size, &name)) + continue; /* not a per-CPU variable */ - if (verbose) - printf("symbol '%s' of address 0x%lx encoded\n", - sym_name, addr); + if (btf_elf__verbose) { + printf("Variable '%s' from CI '%s' at address 0x%lx encoded\n", + name, cu->name, addr); + } /* add a BTF_KIND_VAR in btfe->types */ - linkage = var->external ? BTF_VAR_GLOBAL_ALLOCATED : BTF_VAR_STATIC; - btf_var_id = btf_elf__add_var_type(btfe, type, sym_name, linkage); - if (btf_var_id < 0) { + id = btf_elf__add_var_type(btfe, type, name, linkage); + if (id < 0) { err = -1; - printf("error: failed to encode variable '%s'\n", sym_name); + fprintf(stderr, "error: failed to encode variable '%s' at addr 0x%lx\n", + name, addr); break; } @@ -418,13 +460,12 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, * add a BTF_VAR_SECINFO in btfe->percpu_secinfo, which will be added into * btfe->types later when we add BTF_VAR_DATASEC. */ - type = btf_var_id; offset = addr - btfe->percpu_base_addr; - btf_var_secinfo_id = btf_elf__add_var_secinfo(&btfe->percpu_secinfo, - type, offset, size); - if (btf_var_secinfo_id < 0) { + id = btf_elf__add_var_secinfo(&btfe->percpu_secinfo, id, offset, size); + if (id < 0) { err = -1; - printf("error: failed to encode var secinfo '%s'\n", sym_name); + fprintf(stderr, "error: failed to encode section info for variable '%s' at addr 0x%lx\n", + name, addr); break; } } diff --git a/libbtf.c b/libbtf.c index d74e4eb03393..4829651b76c4 100644 --- a/libbtf.c +++ b/libbtf.c @@ -28,6 +28,7 @@ #include "elf_symtab.h" uint8_t btf_elf__verbose; +uint8_t btf_elf__force; static int btf_var_secinfo_cmp(const void *a, const void *b) { @@ -62,7 +63,6 @@ int btf_elf__load(struct btf_elf *btfe) return 0; } - struct btf_elf *btf_elf__new(const char *filename, Elf *elf) { struct btf_elf *btfe = zalloc(sizeof(*btfe)); @@ -768,10 +768,6 @@ int btf_elf__encode(struct btf_elf *btfe, uint8_t flags) { struct btf *btf = btfe->btf; - if (gobuffer__size(&btfe->percpu_secinfo) != 0) - btf_elf__add_datasec_type(btfe, PERCPU_SECTION, - &btfe->percpu_secinfo); - /* Empty file, nothing to do, so... done! */ if (btf__get_nr_types(btf) == 0) return 0; diff --git a/libbtf.h b/libbtf.h index 9b3d396da31f..887b5bc55c8e 100644 --- a/libbtf.h +++ b/libbtf.h @@ -30,6 +30,7 @@ struct btf_elf { }; extern uint8_t btf_elf__verbose; +extern uint8_t btf_elf__force; #define btf_elf__verbose_log(fmt, ...) { if (btf_elf__verbose) printf(fmt, __VA_ARGS__); } #define PERCPU_SECTION ".data..percpu"