Hi Menglong,
On Fri, 10 Oct 2025 11:38:46 +0800
Menglong Dong <[email protected]> wrote:
> For now, fgraph is used for the fprobe, even if we need trace the entry
> only. However, the performance of ftrace is better than fgraph, and we
> can use ftrace_ops for this case.
>
> Then performance of kprobe-multi increases from 54M to 69M. Before this
> commit:
>
> $ ./benchs/run_bench_trigger.sh kprobe-multi
> kprobe-multi : 54.663 ± 0.493M/s
>
> After this commit:
>
> $ ./benchs/run_bench_trigger.sh kprobe-multi
> kprobe-multi : 69.447 ± 0.143M/s
>
> Mitigation is disable during the bench testing above.
>
Thanks for updating!
This looks good to me. Just a nit comment below;
[...]
> @@ -379,11 +380,82 @@ static void fprobe_return(struct ftrace_graph_ret
> *trace,
> NOKPROBE_SYMBOL(fprobe_return);
>
> static struct fgraph_ops fprobe_graph_ops = {
> - .entryfunc = fprobe_entry,
> + .entryfunc = fprobe_fgraph_entry,
> .retfunc = fprobe_return,
> };
> static int fprobe_graph_active;
>
> +/* ftrace_ops callback, this processes fprobes which have only
> entry_handler. */
> +static void fprobe_ftrace_entry(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *ops, struct ftrace_regs *fregs)
> +{
> + struct fprobe_hlist_node *node;
> + struct rhlist_head *head, *pos;
> + struct fprobe *fp;
> + int bit;
> +
> + bit = ftrace_test_recursion_trylock(ip, parent_ip);
> + if (bit < 0)
> + return;
> +
nit: We'd better to explain why we need this here too;
/*
* ftrace_test_recursion_trylock() disables preemption, but
* rhltable_lookup() checks whether rcu_read_lcok is held.
* So we take rcu_read_lock() here.
*/
> + rcu_read_lock();
> + head = rhltable_lookup(&fprobe_ip_table, &ip, fprobe_rht_params);
> +
> + rhl_for_each_entry_rcu(node, pos, head, hlist) {
> + if (node->addr != ip)
> + break;
> + fp = READ_ONCE(node->fp);
> + if (unlikely(!fp || fprobe_disabled(fp) || fp->exit_handler))
> + continue;
> +
> + if (fprobe_shared_with_kprobes(fp))
> + __fprobe_kprobe_handler(ip, parent_ip, fp, fregs, NULL);
> + else
> + __fprobe_handler(ip, parent_ip, fp, fregs, NULL);
> + }
> + rcu_read_unlock();
> + ftrace_test_recursion_unlock(bit);
> +}
> +NOKPROBE_SYMBOL(fprobe_ftrace_entry);
Thank you,
> +
> +static struct ftrace_ops fprobe_ftrace_ops = {
> + .func = fprobe_ftrace_entry,
> + .flags = FTRACE_OPS_FL_SAVE_REGS,
> +};
> +static int fprobe_ftrace_active;
> +
> +static int fprobe_ftrace_add_ips(unsigned long *addrs, int num)
> +{
> + int ret;
> +
> + lockdep_assert_held(&fprobe_mutex);
> +
> + ret = ftrace_set_filter_ips(&fprobe_ftrace_ops, addrs, num, 0, 0);
> + if (ret)
> + return ret;
> +
> + if (!fprobe_ftrace_active) {
> + ret = register_ftrace_function(&fprobe_ftrace_ops);
> + if (ret) {
> + ftrace_free_filter(&fprobe_ftrace_ops);
> + return ret;
> + }
> + }
> + fprobe_ftrace_active++;
> + return 0;
> +}
> +
> +static void fprobe_ftrace_remove_ips(unsigned long *addrs, int num)
> +{
> + lockdep_assert_held(&fprobe_mutex);
> +
> + fprobe_ftrace_active--;
> + if (!fprobe_ftrace_active)
> + unregister_ftrace_function(&fprobe_ftrace_ops);
> + if (num)
> + ftrace_set_filter_ips(&fprobe_ftrace_ops, addrs, num, 1, 0);
> +}
> +
> /* Add @addrs to the ftrace filter and register fgraph if needed. */
> static int fprobe_graph_add_ips(unsigned long *addrs, int num)
> {
> @@ -498,9 +570,12 @@ static int fprobe_module_callback(struct notifier_block
> *nb,
> } while (node == ERR_PTR(-EAGAIN));
> rhashtable_walk_exit(&iter);
>
> - if (alist.index > 0)
> + if (alist.index > 0) {
> ftrace_set_filter_ips(&fprobe_graph_ops.ops,
> alist.addrs, alist.index, 1, 0);
> + ftrace_set_filter_ips(&fprobe_ftrace_ops,
> + alist.addrs, alist.index, 1, 0);
> + }
> mutex_unlock(&fprobe_mutex);
>
> kfree(alist.addrs);
> @@ -733,7 +808,11 @@ int register_fprobe_ips(struct fprobe *fp, unsigned long
> *addrs, int num)
> mutex_lock(&fprobe_mutex);
>
> hlist_array = fp->hlist_array;
> - ret = fprobe_graph_add_ips(addrs, num);
> + if (fp->exit_handler)
> + ret = fprobe_graph_add_ips(addrs, num);
> + else
> + ret = fprobe_ftrace_add_ips(addrs, num);
> +
> if (!ret) {
> add_fprobe_hash(fp);
> for (i = 0; i < hlist_array->size; i++) {
> @@ -829,7 +908,10 @@ int unregister_fprobe(struct fprobe *fp)
> }
> del_fprobe_hash(fp);
>
> - fprobe_graph_remove_ips(addrs, count);
> + if (fp->exit_handler)
> + fprobe_graph_remove_ips(addrs, count);
> + else
> + fprobe_ftrace_remove_ips(addrs, count);
>
> kfree_rcu(hlist_array, rcu);
> fp->hlist_array = NULL;
> --
> 2.51.0
>
--
Masami Hiramatsu (Google) <[email protected]>
