On 6/25/23 7:34 PM, Carlos Rodriguez-Fernandez wrote:
It allows tools to iterate over CPUs present
in the system that are actually running processes,
which can be less than the number of possible CPUs.
Please add more context here. There exists a bcc issue
https://github.com/iovisor/bcc/issues/4651
which shows the context for this patch set.
Basically it is to address bcc/libbpf-tools/cpufreq
failure in case that some cpus are not present.
Carlos, you need to show what can be done
in tool itself to resolve the issue vs.
to use the API from what is proposed here
to resolve the issue. So it would become
clear how the new API might help or not.
Signed-off-by: Carlos Rodriguez-Fernandez <carlosrodrifernandez@xxxxxxxxx>
---
src/libbpf.c | 32 +++++++++++++++++++++++++++-----
src/libbpf.h | 8 +++++---
2 files changed, 32 insertions(+), 8 deletions(-)
diff --git a/src/libbpf.c b/src/libbpf.c
index 214f828..e42d252 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -12615,14 +12615,26 @@ int parse_cpu_mask_file(const char *fcpu, bool **mask, int *mask_sz)
return parse_cpu_mask_str(buf, mask, mask_sz);
}
-int libbpf_num_possible_cpus(void)
+typedef enum {POSSIBLE=0, PRESENT, NUM_TYPES } CPU_TOPOLOGY_SYSFS_TYPE;
+
+static const char *cpu_topology_sysfs_path_by_type(const CPU_TOPOLOGY_SYSFS_TYPE type) {
+ const static char *possible_sysfs_path = "/sys/devices/system/cpu/possible";
+ const static char *present_sysfs_path = "/sys/devices/system/cpu/present";
+ switch(type) {
+ case POSSIBLE: return possible_sysfs_path;
+ case PRESENT: return present_sysfs_path;
+ default: return possible_sysfs_path;
+ }
+}
+
+int libbpf_num_cpus_by_topology_sysfs_type(const CPU_TOPOLOGY_SYSFS_TYPE type)
{
- static const char *fcpu = "/sys/devices/system/cpu/possible";
- static int cpus;
+ const char *fcpu = cpu_topology_sysfs_path_by_type(type);
+ static int cpus[NUM_TYPES];
int err, n, i, tmp_cpus;
bool *mask;
- tmp_cpus = READ_ONCE(cpus);
+ tmp_cpus = READ_ONCE(cpus[type]);
if (tmp_cpus > 0)
return tmp_cpus;
@@ -12637,10 +12649,20 @@ int libbpf_num_possible_cpus(void)
}
free(mask);
- WRITE_ONCE(cpus, tmp_cpus);
+ WRITE_ONCE(cpus[type], tmp_cpus);
return tmp_cpus;
}
+int libbpf_num_possible_cpus(void)
+{
+ return libbpf_num_cpus_by_topology_sysfs_type(POSSIBLE);
+}
+
+int libbpf_num_present_cpus(void)
+{
+ return libbpf_num_cpus_by_topology_sysfs_type(PRESENT);
+}
+
static int populate_skeleton_maps(const struct bpf_object *obj,
struct bpf_map_skeleton *maps,
size_t map_cnt)
diff --git a/src/libbpf.h b/src/libbpf.h
index 754da73..a34152c 100644
--- a/src/libbpf.h
+++ b/src/libbpf.h
@@ -1433,9 +1433,10 @@ LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type,
enum bpf_func_id helper_id, const void *opts);
/**
- * @brief **libbpf_num_possible_cpus()** is a helper function to get the
- * number of possible CPUs that the host kernel supports and expects.
- * @return number of possible CPUs; or error code on failure
+ * @brief **libbpf_num_possible_cpus()**, and **libbpf_num_present_cpus()**
+ * are helper functions to get the number of possible, and present CPUs respectivelly.
+ * See for more information: https://www.kernel.org/doc/html/latest/admin-guide/cputopology.html
+ * @return number of CPUs; or error code on failure
*
* Example usage:
*
@@ -1447,6 +1448,7 @@ LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type,
* bpf_map_lookup_elem(per_cpu_map_fd, key, values);
*/
LIBBPF_API int libbpf_num_possible_cpus(void);
+LIBBPF_API int libbpf_num_present_cpus(void);
struct bpf_map_skeleton {
const char *name;
