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Date: Thu, 12 Mar 2020 14:41:15 +0100 From: Peter Zijlstra <peterz@...radead.org> To: tglx@...utronix.de, jpoimboe@...hat.com Cc: linux-kernel@...r.kernel.org, x86@...nel.org, peterz@...radead.org Subject: [RFC][PATCH 08/16] Optimize find_section_by_name() In order to avoid yet another linear search of (20k) sections, add a name based hash. This reduces objtool runtime on vmlinux.o by some 10s to around 35s. Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org> --- tools/objtool/elf.c | 9 ++++++++- tools/objtool/elf.h | 3 +++ 2 files changed, 11 insertions(+), 1 deletion(-) --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -22,11 +22,16 @@ #define MAX_NAME_LEN 128 +static inline u32 str_hash(const char *str) +{ + return jhash(str, strlen(str), 0); +} + struct section *find_section_by_name(struct elf *elf, const char *name) { struct section *sec; - list_for_each_entry(sec, &elf->sections, list) + hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name)) if (!strcmp(sec->name, name)) return sec; @@ -193,6 +198,7 @@ static int read_sections(struct elf *elf sec->len = sec->sh.sh_size; hash_add(elf->section_hash, &sec->hash, sec->idx); + hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name)); } if (stats) @@ -433,6 +439,7 @@ struct elf *elf_read(const char *name, i hash_init(elf->symbol_hash); hash_init(elf->section_hash); + hash_init(elf->section_name_hash); INIT_LIST_HEAD(&elf->sections); elf->fd = open(name, flags); --- a/tools/objtool/elf.h +++ b/tools/objtool/elf.h @@ -10,6 +10,7 @@ #include <gelf.h> #include <linux/list.h> #include <linux/hashtable.h> +#include <linux/jhash.h> #ifdef LIBELF_USE_DEPRECATED # define elf_getshdrnum elf_getshnum @@ -26,6 +27,7 @@ struct section { struct list_head list; struct hlist_node hash; + struct hlist_node name_hash; GElf_Shdr sh; struct list_head symbol_list; struct list_head rela_list; @@ -73,6 +75,7 @@ struct elf { struct list_head sections; DECLARE_HASHTABLE(symbol_hash, 20); DECLARE_HASHTABLE(section_hash, 16); + DECLARE_HASHTABLE(section_name_hash, 16); };
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