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Message-ID: <20250923092001.1087678-2-dongml2@chinatelecom.cn>
Date: Tue, 23 Sep 2025 17:20:01 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: mhiramat@...nel.org
Cc: rostedt@...dmis.org,
mathieu.desnoyers@...icios.com,
linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org,
bpf@...r.kernel.org
Subject: [PATCH 2/2] tracing: fprobe: optimization for entry only case
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.
Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
kernel/trace/fprobe.c | 88 +++++++++++++++++++++++++++++++++++++++----
1 file changed, 81 insertions(+), 7 deletions(-)
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 1785fba367c9..de4ae075548d 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -292,7 +292,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
if (node->addr != func)
continue;
fp = READ_ONCE(node->fp);
- if (fp && !fprobe_disabled(fp))
+ if (fp && !fprobe_disabled(fp) && fp->exit_handler)
fp->nmissed++;
}
return 0;
@@ -312,11 +312,11 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
if (node->addr != func)
continue;
fp = READ_ONCE(node->fp);
- if (!fp || fprobe_disabled(fp))
+ if (unlikely(!fp || fprobe_disabled(fp) || !fp->exit_handler))
continue;
data_size = fp->entry_data_size;
- if (data_size && fp->exit_handler)
+ if (data_size)
data = fgraph_data + used + FPROBE_HEADER_SIZE_IN_LONG;
else
data = NULL;
@@ -327,7 +327,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
ret = __fprobe_handler(func, ret_ip, fp, fregs, data);
/* If entry_handler returns !0, nmissed is not counted but skips exit_handler. */
- if (!ret && fp->exit_handler) {
+ if (!ret) {
int size_words = SIZE_IN_LONG(data_size);
if (write_fprobe_header(&fgraph_data[used], fp, size_words))
@@ -384,6 +384,70 @@ static struct fgraph_ops fprobe_graph_ops = {
};
static int fprobe_graph_active;
+/* ftrace_ops backend (entry-only) */
+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;
+
+ guard(rcu)();
+ 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;
+ /* entry-only path: no exit_handler nor per-call data */
+ if (fprobe_shared_with_kprobes(fp))
+ __fprobe_kprobe_handler(ip, parent_ip, fp, fregs, NULL);
+ else
+ __fprobe_handler(ip, parent_ip, fp, fregs, NULL);
+ }
+}
+NOKPROBE_SYMBOL(fprobe_ftrace_entry);
+
+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)
{
@@ -500,9 +564,12 @@ static int fprobe_module_callback(struct notifier_block *nb,
} while (node == ERR_PTR(-EAGAIN));
rhashtable_walk_exit(&iter);
- if (alist.index < alist.size && alist.index > 0)
+ if (alist.index < alist.size && 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);
@@ -735,7 +802,11 @@ 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++) {
@@ -831,7 +902,10 @@ 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
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