objtool: Optimize !vmlinux.o again

When doing kbuild tests to see if the objtool changes affected those I
found that there was a measurable regression:

          pre		  post

  real    1m13.594        1m16.488s
  user    34m58.246s      35m23.947s
  sys     4m0.393s        4m27.312s

Perf showed that for small files the increased hash-table sizes were a
measurable difference. Since we already have -l "vmlinux" to
distinguish between the modes, make it also use a smaller portion of
the hash-tables.

This flips it into a small win:

  real    1m14.143s
  user    34m49.292s
  sys     3m44.746s

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Miroslav Benes <[email protected]>
Reviewed-by: Alexandre Chartre <[email protected]>
Acked-by: Josh Poimboeuf <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: Peter Zijlstra

tools/objtool/elf.c

@@ -27,6 +27,22 @@ static inline u32 str_hash(const char *str)
 	return jhash(str, strlen(str), 0);
 }
 
+static inline int elf_hash_bits(void)
+{
+	return vmlinux ? ELF_HASH_BITS : 16;
+}
+
+#define elf_hash_add(hashtable, node, key) \
+	hlist_add_head(node, &hashtable[hash_min(key, elf_hash_bits())])
+
+static void elf_hash_init(struct hlist_head *table)
+{
+	__hash_init(table, 1U << elf_hash_bits());
+}
+
+#define elf_hash_for_each_possible(name, obj, member, key)			\
+	hlist_for_each_entry(obj, &name[hash_min(key, elf_hash_bits())], member)
+
 static void rb_add(struct rb_root *tree, struct rb_node *node,
 		   int (*cmp)(struct rb_node *, const struct rb_node *))
 {
@@ -115,7 +131,7 @@ struct section *find_section_by_name(struct elf *elf, const char *name)
 {
 	struct section *sec;
 
-	hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name))
+	elf_hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name))
 		if (!strcmp(sec->name, name))
 			return sec;
 
@@ -127,7 +143,7 @@ static struct section *find_section_by_index(struct elf *elf,
 {
 	struct section *sec;
 
-	hash_for_each_possible(elf->section_hash, sec, hash, idx)
+	elf_hash_for_each_possible(elf->section_hash, sec, hash, idx)
 		if (sec->idx == idx)
 			return sec;
 
@@ -138,7 +154,7 @@ static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 {
 	struct symbol *sym;
 
-	hash_for_each_possible(elf->symbol_hash, sym, hash, idx)
+	elf_hash_for_each_possible(elf->symbol_hash, sym, hash, idx)
 		if (sym->idx == idx)
 			return sym;
 
@@ -205,7 +221,7 @@ struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
 {
 	struct symbol *sym;
 
-	hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
+	elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
 		if (!strcmp(sym->name, name))
 			return sym;
 
@@ -224,7 +240,7 @@ struct rela *find_rela_by_dest_range(struct elf *elf, struct section *sec,
 	sec = sec->rela;
 
 	for_offset_range(o, offset, offset + len) {
-		hash_for_each_possible(elf->rela_hash, rela, hash,
+		elf_hash_for_each_possible(elf->rela_hash, rela, hash,
 				       sec_offset_hash(sec, o)) {
 			if (rela->sec != sec)
 				continue;
@@ -309,8 +325,8 @@ static int read_sections(struct elf *elf)
 		sec->len = sec->sh.sh_size;
 
 		list_add_tail(&sec->list, &elf->sections);
-		hash_add(elf->section_hash, &sec->hash, sec->idx);
-		hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
+		elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
+		elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
 	}
 
 	if (stats)
@@ -394,8 +410,8 @@ static int read_symbols(struct elf *elf)
 		else
 			entry = &sym->sec->symbol_list;
 		list_add(&sym->list, entry);
-		hash_add(elf->symbol_hash, &sym->hash, sym->idx);
-		hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name));
+		elf_hash_add(elf->symbol_hash, &sym->hash, sym->idx);
+		elf_hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name));
 	}
 
 	if (stats)
@@ -456,6 +472,14 @@ static int read_symbols(struct elf *elf)
 	return -1;
 }
 
+void elf_add_rela(struct elf *elf, struct rela *rela)
+{
+	struct section *sec = rela->sec;
+
+	list_add_tail(&rela->list, &sec->rela_list);
+	elf_hash_add(elf->rela_hash, &rela->hash, rela_hash(rela));
+}
+
 static int read_relas(struct elf *elf)
 {
 	struct section *sec;
@@ -503,8 +527,7 @@ static int read_relas(struct elf *elf)
 				return -1;
 			}
 
-			list_add_tail(&rela->list, &sec->rela_list);
-			hash_add(elf->rela_hash, &rela->hash, rela_hash(rela));
+			elf_add_rela(elf, rela);
 			nr_rela++;
 		}
 		max_rela = max(max_rela, nr_rela);
@@ -531,15 +554,16 @@ struct elf *elf_read(const char *name, int flags)
 		perror("malloc");
 		return NULL;
 	}
-	memset(elf, 0, sizeof(*elf));
+	memset(elf, 0, offsetof(struct elf, sections));
 
-	hash_init(elf->symbol_hash);
-	hash_init(elf->symbol_name_hash);
-	hash_init(elf->section_hash);
-	hash_init(elf->section_name_hash);
-	hash_init(elf->rela_hash);
 	INIT_LIST_HEAD(&elf->sections);
 
+	elf_hash_init(elf->symbol_hash);
+	elf_hash_init(elf->symbol_name_hash);
+	elf_hash_init(elf->section_hash);
+	elf_hash_init(elf->section_name_hash);
+	elf_hash_init(elf->rela_hash);
+
 	elf->fd = open(name, flags);
 	if (elf->fd == -1) {
 		fprintf(stderr, "objtool: Can't open '%s': %s\n",
@@ -676,8 +700,8 @@ struct section *elf_create_section(struct elf *elf, const char *name,
 	shstrtab->changed = true;
 
 	list_add_tail(&sec->list, &elf->sections);
-	hash_add(elf->section_hash, &sec->hash, sec->idx);
-	hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
+	elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
+	elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
 
 	return sec;
 }

tools/objtool/elf.h

@@ -70,17 +70,19 @@ struct rela {
 	bool jump_table_start;
 };
 
+#define ELF_HASH_BITS	20
+
 struct elf {
 	Elf *elf;
 	GElf_Ehdr ehdr;
 	int fd;
 	char *name;
 	struct list_head sections;
-	DECLARE_HASHTABLE(symbol_hash, 20);
-	DECLARE_HASHTABLE(symbol_name_hash, 20);
-	DECLARE_HASHTABLE(section_hash, 16);
-	DECLARE_HASHTABLE(section_name_hash, 16);
-	DECLARE_HASHTABLE(rela_hash, 20);
+	DECLARE_HASHTABLE(symbol_hash, ELF_HASH_BITS);
+	DECLARE_HASHTABLE(symbol_name_hash, ELF_HASH_BITS);
+	DECLARE_HASHTABLE(section_hash, ELF_HASH_BITS);
+	DECLARE_HASHTABLE(section_name_hash, ELF_HASH_BITS);
+	DECLARE_HASHTABLE(rela_hash, ELF_HASH_BITS);
 };
 
 #define OFFSET_STRIDE_BITS	4
@@ -127,6 +129,7 @@ struct section *elf_create_rela_section(struct elf *elf, struct section *base);
 int elf_rebuild_rela_section(struct section *sec);
 int elf_write(struct elf *elf);
 void elf_close(struct elf *elf);
+void elf_add_rela(struct elf *elf, struct rela *rela);
 
 #define for_each_sec(file, sec)						\
 	list_for_each_entry(sec, &file->elf->sections, list)

tools/objtool/orc_gen.c

@@ -130,8 +130,7 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, struct secti
 	rela->offset = idx * sizeof(int);
 	rela->sec = ip_relasec;
 
-	list_add_tail(&rela->list, &ip_relasec->rela_list);
-	hash_add(elf->rela_hash, &rela->hash, rela_hash(rela));
+	elf_add_rela(elf, rela);
 
 	return 0;
 }