[RFC PATCH v2 1/5] btf: search local BTF before base BTF

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

Change btf_find_by_name_kind() to search the local BTF first,
then fall back to the base BTF. This can skip traversing the large
vmlinux BTF when the target type resides in a kernel module's BTF,
thereby significantly improving lookup performance.

In a test searching for the btf_type of function ext2_new_inode
located in the ext2 kernel module:

Before: 408631 ns
After:     499 ns

Performance improvement: ~819x faster

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>
Signed-off-by: pengdonglin <pengdonglin@xiaomi.com>
Signed-off-by: Donglin Peng <dolinux.peng@gmail.com>
---
 include/linux/btf.h |  1 +
 kernel/bpf/btf.c    | 27 ++++++++++++++++++---------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index f06976ffb63f..ddc53a7ac7cd 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -220,6 +220,7 @@ bool btf_is_module(const struct btf *btf);
 bool btf_is_vmlinux(const struct btf *btf);
 struct module *btf_try_get_module(const struct btf *btf);
 u32 btf_nr_types(const struct btf *btf);
+u32 btf_type_cnt(const struct btf *btf);
 struct btf *btf_base_btf(const struct btf *btf);
 bool btf_type_is_i32(const struct btf_type *t);
 bool btf_type_is_i64(const struct btf_type *t);
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0de8fc8a0e0b..c414cf37e1bd 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -544,22 +544,31 @@ u32 btf_nr_types(const struct btf *btf)
 	return total;
 }
 
+u32 btf_type_cnt(const struct btf *btf)
+{
+	return btf->start_id + btf->nr_types;
+}
+
 s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind)
 {
 	const struct btf_type *t;
 	const char *tname;
 	u32 i, total;
 
-	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;
+	do {
+		total = btf_type_cnt(btf);
+		for (i = btf->start_id; 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;
-	}
+			tname = btf_name_by_offset(btf, t->name_off);
+			if (!strcmp(tname, name))
+				return i;
+		}
+
+		btf = btf->base_btf;
+	} while (btf);
 
 	return -ENOENT;
 }
-- 
2.34.1