Re: [PATCH v2 1/2] tracing: fprobe: optimization for entry only case
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Date: 2025-10-12 04:07:15
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Hi Menglong, On Fri, 10 Oct 2025 11:38:46 +0800 Menglong Dong [off-list ref] 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; [...]
quoted hunk ↗ jump to hunk
@@ -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,
quoted hunk ↗ jump to hunk
+ +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) [off-list ref]