[RFC PATCH v7 6/7] btf: Optimize type lookup with binary search

[Donglin Peng <dolinux.peng@gmail.com>]

From: Donglin Peng <pengdonglin@xiaomi.com>

Improve btf_find_by_name_kind() performance by adding binary search
support for sorted types. Falls back to linear search for compatibility.

Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Song Liu <song@kernel.org>
Cc: Xiaoqin Zhang <zhangxiaoqin@xiaomi.com>
Signed-off-by: Donglin Peng <pengdonglin@xiaomi.com>
---
 kernel/bpf/btf.c | 83 ++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 73 insertions(+), 10 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0de8fc8a0e0b..5dd2c40d4874 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -259,6 +259,7 @@ struct btf {
 	void *nohdr_data;
 	struct btf_header hdr;
 	u32 nr_types; /* includes VOID for base BTF */
+	u32 nr_sorted_types; /* exclude VOID for base BTF */
 	u32 types_size;
 	u32 data_size;
 	refcount_t refcnt;
@@ -494,6 +495,11 @@ static bool btf_type_is_modifier(const struct btf_type *t)
 	return false;
 }
 
+static int btf_start_id(const struct btf *btf)
+{
+	return btf->start_id + (btf->base_btf ? 0 : 1);
+}
+
 bool btf_type_is_void(const struct btf_type *t)
 {
 	return t == &btf_void;
@@ -544,24 +550,78 @@ u32 btf_nr_types(const struct btf *btf)
 	return total;
 }
 
+static s32 btf_find_by_name_kind_bsearch(const struct btf *btf, const char *name,
+						s32 start_id, s32 end_id)
+{
+	const struct btf_type *t;
+	const char *tname;
+	s32 l, r, m;
+
+	l = start_id;
+	r = end_id;
+	while (l <= r) {
+		m = l + (r - l) / 2;
+		t = btf_type_by_id(btf, m);
+		tname = btf_name_by_offset(btf, t->name_off);
+		if (strcmp(tname, name) >= 0) {
+			if (l == r)
+				return r;
+			r = m;
+		} else {
+			l = m + 1;
+		}
+	}
+
+	return btf_nr_types(btf);
+}
+
 s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind)
 {
+	const struct btf *base_btf = btf_base_btf(btf);
 	const struct btf_type *t;
 	const char *tname;
-	u32 i, total;
+	int err = -ENOENT;
 
-	total = btf_nr_types(btf);
-	for (i = 1; i < total; i++) {
-		t = btf_type_by_id(btf, i);
-		if (BTF_INFO_KIND(t->info) != kind)
-			continue;
+	if (base_btf) {
+		err = btf_find_by_name_kind(base_btf, name, kind);
+		if (err > 0)
+			goto out;
+	}
 
-		tname = btf_name_by_offset(btf, t->name_off);
-		if (!strcmp(tname, name))
-			return i;
+	if (btf->nr_sorted_types > 0) {
+		/* binary search */
+		s32 start_id, end_id;
+		u32 idx;
+
+		start_id = btf_start_id(btf);
+		end_id = start_id + btf->nr_sorted_types - 1;
+		idx = btf_find_by_name_kind_bsearch(btf, name, start_id, end_id);
+		for (; idx <= end_id; idx++) {
+			t = btf_type_by_id(btf, idx);
+			tname = btf_name_by_offset(btf, t->name_off);
+			if (strcmp(tname, name))
+				goto out;
+			if (BTF_INFO_KIND(t->info) == kind)
+				return idx;
+		}
+	} else {
+		/* linear search */
+		u32 i, total;
+
+		total = btf_nr_types(btf);
+		for (i = btf_start_id(btf); i < total; i++) {
+			t = btf_type_by_id(btf, i);
+			if (BTF_INFO_KIND(t->info) != kind)
+				continue;
+
+			tname = btf_name_by_offset(btf, t->name_off);
+			if (!strcmp(tname, name))
+				return i;
+		}
 	}
 
-	return -ENOENT;
+out:
+	return err;
 }
 
 s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
@@ -5791,6 +5851,7 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat
 		goto errout;
 	}
 	env->btf = btf;
+	btf->nr_sorted_types = 0;
 
 	data = kvmalloc(attr->btf_size, GFP_KERNEL | __GFP_NOWARN);
 	if (!data) {
@@ -6210,6 +6271,7 @@ static struct btf *btf_parse_base(struct btf_verifier_env *env, const char *name
 	btf->data = data;
 	btf->data_size = data_size;
 	btf->kernel_btf = true;
+	btf->nr_sorted_types = 0;
 	snprintf(btf->name, sizeof(btf->name), "%s", name);
 
 	err = btf_parse_hdr(env);
@@ -6327,6 +6389,7 @@ static struct btf *btf_parse_module(const char *module_name, const void *data,
 	btf->start_id = base_btf->nr_types;
 	btf->start_str_off = base_btf->hdr.str_len;
 	btf->kernel_btf = true;
+	btf->nr_sorted_types = 0;
 	snprintf(btf->name, sizeof(btf->name), "%s", module_name);
 
 	btf->data = kvmemdup(data, data_size, GFP_KERNEL | __GFP_NOWARN);
-- 
2.34.1