This patch switches libbpf_num_possible_cpus() from using possible CPU
set to present CPU set. This fixes issues with incorrect auto-sizing of
PERF_EVENT_ARRAY map on HOTPLUG-enabled systems.
On HOTPLUG enabled systems, /sys/devices/system/cpu/possible is going to
be a set of any representable (i.e., potentially possible) CPU, which is
normally way higher than real amount of CPUs (e.g., 0-127 on VM I've
tested on, while there were just two CPU cores actually present).
/sys/devices/system/cpu/present, on the other hand, will only contain
CPUs that are physically present in the system (even if not online yet),
which is what we really want, especially when creating per-CPU maps or
perf events.
On systems with HOTPLUG disabled, present and possible are identical, so
there is no change of behavior there.
Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
---
tools/lib/bpf/libbpf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e0276520171b..45351c074e45 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5899,7 +5899,7 @@ void bpf_program__bpil_offs_to_addr(struct bpf_prog_info_linear *info_linear)
int libbpf_num_possible_cpus(void)
{
- static const char *fcpu = "/sys/devices/system/cpu/possible";
+ static const char *fcpu = "/sys/devices/system/cpu/present";
int len = 0, n = 0, il = 0, ir = 0;
unsigned int start = 0, end = 0;
int tmp_cpus = 0;
--
2.17.1
