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libbpf: auto-set PERF_EVENT_ARRAY size to number of CPUs 

For BPF_MAP_TYPE_PERF_EVENT_ARRAY typically correct size is number of
possible CPUs. This is impossible to specify at compilation time. This
change adds automatic setting of PERF_EVENT_ARRAY size to number of
system CPUs, unless non-zero size is specified explicitly. This allows
to adjust size for advanced specific cases, while providing convenient
and logical defaults.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Andrii Nakryiko 2019-07-06 11:06:25 -07:00 committed by Daniel Borkmann
parent fb84b82246
commit d7ff34d5fb
1 changed files with 24 additions and 7 deletions
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31
tools/lib/bpf/libbpf.c
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@ -2116,6 +2116,7 @@ static int
bpf_object__create_maps(struct bpf_object *obj)
{
struct bpf_create_map_attr create_attr = {};
int nr_cpus = 0;
unsigned int i;
int err;
@ -2138,7 +2139,22 @@ bpf_object__create_maps(struct bpf_object *obj)
create_attr.map_flags = def->map_flags;
create_attr.key_size = def->key_size;
create_attr.value_size = def->value_size;
create_attr.max_entries = def->max_entries;
if (def->type == BPF_MAP_TYPE_PERF_EVENT_ARRAY &&
!def->max_entries) {
if (!nr_cpus)
nr_cpus = libbpf_num_possible_cpus();
if (nr_cpus < 0) {
pr_warning("failed to determine number of system CPUs: %d\n",
nr_cpus);
err = nr_cpus;
goto err_out;
}
pr_debug("map '%s': setting size to %d\n",
map->name, nr_cpus);
create_attr.max_entries = nr_cpus;
} else {
create_attr.max_entries = def->max_entries;
}
create_attr.btf_fd = 0;
create_attr.btf_key_type_id = 0;
create_attr.btf_value_type_id = 0;
@ -2155,9 +2171,10 @@ bpf_object__create_maps(struct bpf_object *obj)
*pfd = bpf_create_map_xattr(&create_attr);
if (*pfd < 0 && (create_attr.btf_key_type_id ||
create_attr.btf_value_type_id)) {
cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
err = -errno;
cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
pr_warning("Error in bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n",
map->name, cp, errno);
map->name, cp, err);
create_attr.btf_fd = 0;
create_attr.btf_key_type_id = 0;
create_attr.btf_value_type_id = 0;
@ -2169,11 +2186,11 @@ bpf_object__create_maps(struct bpf_object *obj)
if (*pfd < 0) {
size_t j;
err = *pfd;
err = -errno;
err_out:
cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
pr_warning("failed to create map (name: '%s'): %s\n",
map->name, cp);
cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
pr_warning("failed to create map (name: '%s'): %s(%d)\n",
map->name, cp, err);
for (j = 0; j < i; j++)
zclose(obj->maps[j].fd);
return err;