On Thu, Jan 05, 2023 at 10:31:12PM +0100, Jiri Olsa wrote:
> On Wed, Jan 04, 2023 at 05:25:08PM +0100, Petr Mladek wrote:
> > On Fri 2022-12-30 19:27:28, Zhen Lei wrote:
> > > Function __module_address() can quickly return the pointer of the module
> > > to which an address belongs. We do not need to traverse the symbols of all
> > > modules to check whether each address in addrs[] is the start address of
> > > the corresponding symbol, because register_fprobe_ips() will do this check
> > > later.
>
> hum, for some reason I can see only replies to this patch and
> not the actual patch.. I'll dig it out of the lore I guess
>
> > >
> > > Assuming that there are m modules, each module has n symbols on average,
> > > and the number of addresses 'addrs_cnt' is abbreviated as K. Then the time
> > > complexity of the original method is O(K * log(K)) + O(m * n * log(K)),
> > > and the time complexity of current method is O(K * (log(m) + M)), M <= m.
> > > (m * n * log(K)) / (K * m) ==> n / log2(K). Even if n is 10 and K is 128,
> > > the ratio is still greater than 1. Therefore, the new method will
> > > generally have better performance.
>
> could you try to benchmark that? I tried something similar but was not
> able to get better performance
hm looks like I tried the smilar thing (below) like you did,
but wasn't able to get better performace
I guess your goal is to get rid of the module arg in
module_kallsyms_on_each_symbol callback that we use?
I'm ok with the change if the performace is not worse
jirka
---
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 5b9008bc597b..3280c22009f1 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2692,23 +2692,16 @@ struct module_addr_args {
int mods_cap;
};
-static int module_callback(void *data, const char *name,
- struct module *mod, unsigned long addr)
+static int add_module(struct module_addr_args *args, struct module *mod)
{
- struct module_addr_args *args = data;
struct module **mods;
- /* We iterate all modules symbols and for each we:
- * - search for it in provided addresses array
- * - if found we check if we already have the module pointer stored
- * (we iterate modules sequentially, so we can check just the last
- * module pointer)
+ /* We iterate sorted addresses and for each within module we:
+ * - check if we already have the module pointer stored for it
+ * (we iterate sorted addresses sequentially, so we can check
+ * just the last module pointer)
* - take module reference and store it
*/
- if (!bsearch(&addr, args->addrs, args->addrs_cnt, sizeof(addr),
- bpf_kprobe_multi_addrs_cmp))
- return 0;
-
if (args->mods && args->mods[args->mods_cnt - 1] == mod)
return 0;
@@ -2734,10 +2727,24 @@ static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u3
.addrs = addrs,
.addrs_cnt = addrs_cnt,
};
- int err;
+ u32 i, err = 0;
+
+ for (i = 0; !err && i < addrs_cnt; i++) {
+ struct module *mod;
+ bool found = false;
+
+ preempt_disable();
+ mod = __module_text_address(addrs[i]);
+ found = mod && try_module_get(mod);
+ preempt_enable();
+
+ if (found) {
+ err = add_module(&args, mod);
+ module_put(mod);
+ }
+ }
/* We return either err < 0 in case of error, ... */
- err = module_kallsyms_on_each_symbol(module_callback, &args);
if (err) {
kprobe_multi_put_modules(args.mods, args.mods_cnt);
kfree(args.mods);
@@ -2862,7 +2869,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
} else {
/*
* We need to sort addrs array even if there are no cookies
- * provided, to allow bsearch in get_modules_for_addrs.
+ * provided, to allow sequential address walk in
+ * get_modules_for_addrs.
*/
sort(addrs, cnt, sizeof(*addrs),
bpf_kprobe_multi_addrs_cmp, NULL);
