On Thu, Oct 22, 2020 at 10:21:29AM +0200, Jiri Olsa wrote:
> The kallsyms_expand_symbol function showed in several bpf related
> profiles, because it's doing linear search.
>
> Before:
>
> Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s* \
> { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
>
> 2,535,458,767 cycles:k ( +- 0.55% )
> 940,046,382 cycles:u ( +- 0.27% )
>
> 33.60 +- 3.27 seconds time elapsed ( +- 9.73% )
>
> Loading all the vmlinux symbols in rbtree and and switch to rbtree
> search in kallsyms_lookup_name function to save few cycles and time.
>
> After:
>
> Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s* \
> { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
>
> 2,199,433,771 cycles:k ( +- 0.55% )
> 936,105,469 cycles:u ( +- 0.37% )
>
> 26.48 +- 3.57 seconds time elapsed ( +- 13.49% )
>
> Each symbol takes 160 bytes, so for my .config I've got about 18 MBs
> used for 115285 symbols.
>
> Signed-off-by: Jiri Olsa <jo...@kernel.org>
FYI there's init_kprobes dependency on kallsyms_lookup_name in early
init call, so this won't work as it is :-\ will address this in v2
also I'll switch to sorted array and bsearch, because kallsyms is not
dynamically updated
jirka
> ---
> kernel/kallsyms.c | 95 ++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 86 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 4fb15fa96734..107c8284170e 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -50,6 +50,36 @@ extern const u16 kallsyms_token_index[] __weak;
>
> extern const unsigned int kallsyms_markers[] __weak;
>
> +static struct kmem_cache *symbol_cachep;
> +
> +struct symbol {
> + char name[KSYM_NAME_LEN];
> + unsigned long addr;
> + struct rb_node rb_node;
> +};
> +
> +static struct rb_root symbols_root = RB_ROOT;
> +
> +static struct symbol *find_symbol(const char *name)
> +{
> + struct symbol *sym;
> + struct rb_node *n;
> + int err;
> +
> + n = symbols_root.rb_node;
> + while (n) {
> + sym = rb_entry(n, struct symbol, rb_node);
> + err = strcmp(name, sym->name);
> + if (err < 0)
> + n = n->rb_left;
> + else if (err > 0)
> + n = n->rb_right;
> + else
> + return sym;
> + }
> + return NULL;
> +}
> +
> /*
> * Expand a compressed symbol data into the resulting uncompressed string,
> * if uncompressed string is too long (>= maxlen), it will be truncated,
> @@ -164,16 +194,12 @@ static unsigned long kallsyms_sym_address(int idx)
> /* Lookup the address for this symbol. Returns 0 if not found. */
> unsigned long kallsyms_lookup_name(const char *name)
> {
> - char namebuf[KSYM_NAME_LEN];
> - unsigned long i;
> - unsigned int off;
> + struct symbol *sym;
>
> - for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
> - off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
> + sym = find_symbol(name);
> + if (sym)
> + return sym->addr;
>
> - if (strcmp(namebuf, name) == 0)
> - return kallsyms_sym_address(i);
> - }
> return module_kallsyms_lookup_name(name);
> }
>
> @@ -743,9 +769,60 @@ static const struct proc_ops kallsyms_proc_ops = {
> .proc_release = seq_release_private,
> };
>
> +static bool __init add_symbol(struct symbol *new)
> +{
> + struct rb_node *parent = NULL;
> + struct rb_node **p;
> + struct symbol *sym;
> + int err;
> +
> + p = &symbols_root.rb_node;
> +
> + while (*p != NULL) {
> + parent = *p;
> + sym = rb_entry(parent, struct symbol, rb_node);
> + err = strcmp(new->name, sym->name);
> + if (err < 0)
> + p = &(*p)->rb_left;
> + else if (err > 0)
> + p = &(*p)->rb_right;
> + else
> + return false;
> + }
> +
> + rb_link_node(&new->rb_node, parent, p);
> + rb_insert_color(&new->rb_node, &symbols_root);
> + return true;
> +}
> +
> +static int __init kallsyms_name_search_init(void)
> +{
> + bool sym_added = true;
> + struct symbol *sym;
> + unsigned int off;
> + unsigned long i;
> +
> + symbol_cachep = KMEM_CACHE(symbol, SLAB_PANIC|SLAB_ACCOUNT);
> +
> + for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
> + if (sym_added) {
> + sym = kmem_cache_alloc(symbol_cachep, GFP_KERNEL);
> + if (!sym)
> + return -ENOMEM;
> + }
> + off = kallsyms_expand_symbol(off, sym->name,
> ARRAY_SIZE(sym->name));
> + sym->addr = kallsyms_sym_address(i);
> + sym_added = add_symbol(sym);
> + }
> +
> + if (!sym_added)
> + kmem_cache_free(symbol_cachep, sym);
> + return 0;
> +}
> +
> static int __init kallsyms_init(void)
> {
> proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
> - return 0;
> + return kallsyms_name_search_init();
> }
> device_initcall(kallsyms_init);
> --
> 2.26.2
>
