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Message-Id: <20241029002208.1947947-4-dolinux.peng@gmail.com>
Date: Tue, 29 Oct 2024 08:22:08 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: andrii@...nel.org,
eddyz87@...il.com
Cc: ast@...nel.org,
rostedt@...dmis.org,
mhiramat@...nel.org,
bpf@...r.kernel.org,
linux-trace-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org,
Donglin Peng <dolinux.peng@...il.com>
Subject: [PATCH v4 3/3] libbpf: Using binary search to improve the performance of btf__find_by_name_kind
Currently, we are only using the linear search method to find the type id
by the name, which has a time complexity of O(n). This change involves
sorting the names of btf types in ascending order and using binary search,
which has a time complexity of O(log(n)).
Another change is the search direction, where we search the BTF first and
then its base.
Signed-off-by: Donglin Peng <dolinux.peng@...il.com>
---
tools/lib/bpf/btf.c | 159 ++++++++++++++++++++++++++++++++++++++------
1 file changed, 140 insertions(+), 19 deletions(-)
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 5290e9d59997..cbf88a6b92e5 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -94,6 +94,10 @@ struct btf {
* - for split BTF counts number of types added on top of base BTF.
*/
__u32 nr_types;
+ /* number of types in this BTF instance which are sorted by name:
+ * - doesn't include special [0] void type;
+ */
+ __u32 nr_types_sorted;
/* if not NULL, points to the base BTF on top of which the current
* split BTF is based
*/
@@ -896,46 +900,111 @@ int btf__resolve_type(const struct btf *btf, __u32 type_id)
return type_id;
}
-__s32 btf__find_by_name(const struct btf *btf, const char *type_name)
+static __s32 btf__find_by_name_bsearch(const struct btf *btf, const char *name,
+ int *start, int *end)
{
- __u32 i, nr_types = btf__type_cnt(btf);
+ const struct btf_type *t;
+ const char *name_buf;
+ int low, low_start, mid, high, high_end;
+ int ret;
+
+ low_start = low = btf->start_id;
+ high_end = high = btf->start_id + btf->nr_types_sorted - 1;
+
+ while (low <= high) {
+ mid = low + (high - low) / 2;
+ t = btf__type_by_id(btf, mid);
+ name_buf = btf__name_by_offset(btf, t->name_off);
+ ret = strcmp(name, name_buf);
+ if (ret > 0)
+ low = mid + 1;
+ else if (ret < 0)
+ high = mid - 1;
+ else
+ break;
+ }
- if (!strcmp(type_name, "void"))
- return 0;
+ if (low > high)
+ return -ESRCH;
- for (i = 1; i < nr_types; i++) {
- const struct btf_type *t = btf__type_by_id(btf, i);
- const char *name = btf__name_by_offset(btf, t->name_off);
+ if (start) {
+ low = mid;
+ while (low > low_start) {
+ t = btf__type_by_id(btf, low-1);
+ name_buf = btf__name_by_offset(btf, t->name_off);
+ if (strcmp(name, name_buf))
+ break;
+ low--;
+ }
+ *start = low;
+ }
- if (name && !strcmp(type_name, name))
- return i;
+ if (end) {
+ high = mid;
+ while (high < high_end) {
+ t = btf__type_by_id(btf, high+1);
+ name_buf = btf__name_by_offset(btf, t->name_off);
+ if (strcmp(name, name_buf))
+ break;
+ high++;
+ }
+ *end = high;
}
- return libbpf_err(-ENOENT);
+ return mid;
}
static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,
const char *type_name, __u32 kind)
{
- __u32 i, nr_types = btf__type_cnt(btf);
+ const struct btf_type *t;
+ const char *tname;
+ int start, end, id;
+ __u32 nr_types;
if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
return 0;
- for (i = start_id; i < nr_types; i++) {
- const struct btf_type *t = btf__type_by_id(btf, i);
- const char *name;
-
- if (btf_kind(t) != kind)
+ while (btf) {
+ if (btf->start_id < start_id) {
+ btf = btf->base_btf;
continue;
- name = btf__name_by_offset(btf, t->name_off);
- if (name && !strcmp(type_name, name))
- return i;
+ }
+
+ if (btf->nr_types_sorted) {
+ id = btf__find_by_name_bsearch(btf, type_name, &start, &end);
+ if (id > 0) {
+ while (start <= end) {
+ t = btf__type_by_id(btf, start);
+ if (kind == BTF_KIND_MAX ||
+ btf_kind(t) == kind)
+ return start;
+ start++;
+ }
+ }
+ } else {
+ nr_types = btf__type_cnt(btf);
+ for (id = btf->start_id; id < nr_types; id++) {
+ t = btf__type_by_id(btf, id);
+ if (kind != BTF_KIND_MAX && btf_kind(t) != kind)
+ continue;
+
+ tname = btf__name_by_offset(btf, t->name_off);
+ if (tname && !strcmp(tname, type_name))
+ return id;
+ }
+ }
+ btf = btf__base_btf(btf);
}
return libbpf_err(-ENOENT);
}
+__s32 btf__find_by_name(const struct btf *btf, const char *type_name)
+{
+ return btf_find_by_name_kind(btf, 1, type_name, BTF_KIND_MAX);
+}
+
__s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name,
__u32 kind)
{
@@ -989,6 +1058,7 @@ static struct btf *btf_new_empty(struct btf *base_btf)
return ERR_PTR(-ENOMEM);
btf->nr_types = 0;
+ btf->nr_types_sorted = 0;
btf->start_id = 1;
btf->start_str_off = 0;
btf->fd = -1;
@@ -1032,6 +1102,53 @@ struct btf *btf__new_empty_split(struct btf *base_btf)
return libbpf_ptr(btf_new_empty(base_btf));
}
+static int btf_check_sort(struct btf *btf, __u32 start_id)
+{
+ __u32 i, n, nr_names = 0;
+
+ n = btf__type_cnt(btf);
+ for (i = start_id; i < n; i++) {
+ const struct btf_type *t;
+ const char *name;
+
+ t = btf__type_by_id(btf, i);
+ if (!t)
+ return libbpf_err(-EINVAL);
+
+ name = btf__str_by_offset(btf, t->name_off);
+ if (!str_is_empty(name))
+ nr_names++;
+ }
+
+ for (i = 0; i < nr_names - 1; i++) {
+ const struct btf_type *t1, *t2;
+ const char *s1, *s2;
+
+ t1 = btf__type_by_id(btf, start_id + i);
+ if (!t1)
+ return libbpf_err(-EINVAL);
+
+ s1 = btf__str_by_offset(btf, t1->name_off);
+ if (str_is_empty(s1))
+ goto out;
+
+ t2 = btf__type_by_id(btf, start_id + i + 1);
+ if (!t2)
+ return libbpf_err(-EINVAL);
+
+ s2 = btf__str_by_offset(btf, t2->name_off);
+ if (str_is_empty(s2))
+ goto out;
+
+ if (strcmp(s1, s2) > 0)
+ goto out;
+ }
+
+ btf->nr_types_sorted = nr_names;
+out:
+ return 0;
+}
+
static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
{
struct btf *btf;
@@ -1042,6 +1159,7 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
return ERR_PTR(-ENOMEM);
btf->nr_types = 0;
+ btf->nr_types_sorted = 0;
btf->start_id = 1;
btf->start_str_off = 0;
btf->fd = -1;
@@ -1071,6 +1189,7 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
err = btf_parse_str_sec(btf);
err = err ?: btf_parse_type_sec(btf);
err = err ?: btf_sanity_check(btf);
+ err = err ?: btf_check_sort(btf, btf->start_id);
if (err)
goto done;
@@ -1690,6 +1809,8 @@ static int btf_ensure_modifiable(struct btf *btf)
btf->types_data_cap = btf->hdr->type_len;
btf->strs_data = NULL;
btf->strs_set = set;
+ /* clear when splitting */
+ btf->nr_types_sorted = 0;
/* if BTF was created from scratch, all strings are guaranteed to be
* unique and deduplicated
*/
--
2.34.1
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