[RFC][PATCH v2 16/16] objtool: Optimize !vmlinux.o again

Peter Zijlstra
2020-03-12T21:57:39Z

Turns out I lost a refresh on this one.

---
Subject: objtool: Optimize !vmlinux.o again
From: Peter Zijlstra <peterz@infradead.org>
Date: Thu Mar 12 14:29:38 CET 2020

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) <peterz@infradead.org>
---
tools/objtool/elf.c | 51 ++++++++++++++++++++++++++++++++++-----------------
tools/objtool/elf.h | 4 ++--
2 files changed, 36 insertions(+), 19 deletions(-)

--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -27,6 +27,22 @@ static inline u32 str_hash(const char *s
return jhash(str, strlen(str), 0);
}

+static inline int elf_hash_bits(void)
+{
+ return vmlinux ? 20 : 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(str
{
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_i
{
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_ind
{
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;

@@ -194,7 +210,7 @@ struct symbol *find_symbol_by_name(struc
{
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;

@@ -213,7 +229,7 @@ struct rela *find_rela_by_dest_range(str
sec = sec->rela;

for (o = offset & RELA_STRIDE_MASK; o < offset + len; o += RELA_STRIDE) {
- hash_for_each_possible(sec->elf->rela_hash, rela, hash,
+ elf_hash_for_each_possible(sec->elf->rela_hash, rela, hash,
__rela_hash(o, sec->idx)) {
if (rela->sec != sec)
continue;
@@ -300,8 +316,8 @@ 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));
+ 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)
@@ -387,8 +403,8 @@ static int read_symbols(struct elf *elf)
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)
@@ -497,7 +513,7 @@ static int read_relas(struct elf *elf)
}

list_add_tail(&rela->list, &sec->rela_list);
- hash_add(elf->rela_hash, &rela->hash, rela_hash(rela));
+ elf_hash_add(elf->rela_hash, &rela->hash, rela_hash(rela));
nr_rela++;
}
max_rela = max(max_rela, nr_rela);
@@ -524,15 +540,16 @@ struct elf *elf_read(const char *name, i
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",
@@ -671,7 +688,7 @@ struct section *elf_create_section(struc
shstrtab->len += strlen(name) + 1;
shstrtab->changed = true;

- hash_add(elf->section_hash, &sec->hash, sec->idx);
+ elf_hash_add(elf->section_hash, &sec->hash, sec->idx);

return sec;
}
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -81,8 +81,8 @@ struct elf {
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(section_hash, 20);
+ DECLARE_HASHTABLE(section_name_hash, 20);
DECLARE_HASHTABLE(rela_hash, 20);
};