preconfigure cpuset with required resources

if we already know the cpuset, then we should preconfigure the newly created cgroup with
those values, instead of using the parent's set. This prevents needless churn in the kernel
as it tracks which CPUs have load balancing disabled.

Signed-off-by: Peter Hunt <[email protected]>

src/libcrun/cgroup-internal.h

@@ -81,6 +81,7 @@ convert_shares_to_weight (uint64_t shares)
 }
 
 int initialize_cpuset_subsystem (const char *path, libcrun_error_t *err);
+int initialize_cpuset_subsystem_resources (const char *path, libcrun_error_t *err, runtime_spec_schema_config_linux_resources *resources);
 
 int write_cpuset_resources (int dirfd_cpuset, int cgroup2, runtime_spec_schema_config_linux_resources_cpu *cpu, libcrun_error_t *err);
 

src/libcrun/cgroup-setup.c

@@ -40,7 +40,7 @@
 #include <libgen.h>
 
 static int
-initialize_cpuset_subsystem_rec (char *path, size_t path_len, char *cpus, char *mems, libcrun_error_t *err)
+initialize_cpuset_subsystem_rec (char *path, size_t path_len, char *cpus, char *mems, runtime_spec_schema_config_linux_resources *resources, libcrun_error_t *err )
 {
   cleanup_close int dirfd = -1;
   cleanup_close int mems_fd = -1;
@@ -95,7 +95,7 @@ initialize_cpuset_subsystem_rec (char *path, size_t path_len, char *cpus, char *
         return 0;
 
       path[parent_path_len] = '\0';
-      ret = initialize_cpuset_subsystem_rec (path, parent_path_len, cpus, mems, err);
+      ret = initialize_cpuset_subsystem_rec (path, parent_path_len, cpus, mems, resources, err);
       path[parent_path_len] = '/';
       if (UNLIKELY (ret < 0))
         {
@@ -104,6 +104,15 @@ initialize_cpuset_subsystem_rec (char *path, size_t path_len, char *cpus, char *
         }
     }
 
+  /* If we know the resources, use them, instead of initializing with the full set, only to revert it later. */
+  if (resources && resources->cpu)
+    {
+      if (resources->cpu->cpus)
+        cpus = xstrdup (resources->cpu->cpus);
+      if (resources->cpu->mems)
+        mems = xstrdup (resources->cpu->mems);
+    }
+
   if (cpus_fd >= 0)
     {
       b_len = TEMP_FAILURE_RETRY (write (cpus_fd, cpus, strlen (cpus)));
@@ -129,7 +138,18 @@ initialize_cpuset_subsystem (const char *path, libcrun_error_t *err)
   char mems_buf[257];
 
   cpus_buf[0] = mems_buf[0] = '\0';
-  return initialize_cpuset_subsystem_rec (tmp_path, strlen (tmp_path), cpus_buf, mems_buf, err);
+  return initialize_cpuset_subsystem_rec (tmp_path, strlen (tmp_path), cpus_buf, mems_buf, NULL, err);
+}
+
+int
+initialize_cpuset_subsystem_resources (const char *path, libcrun_error_t *err, runtime_spec_schema_config_linux_resources *resources)
+{
+  cleanup_free char *tmp_path = xstrdup (path);
+  char cpus_buf[257];
+  char mems_buf[257];
+
+  cpus_buf[0] = mems_buf[0] = '\0';
+  return initialize_cpuset_subsystem_rec (tmp_path, strlen (tmp_path), cpus_buf, mems_buf, resources, err);
 }
 
 static int

src/libcrun/cgroup-systemd.c

@@ -252,7 +252,7 @@ setup_cpuset_for_systemd_v1 (runtime_spec_schema_config_linux_resources *resourc
   if (UNLIKELY (ret < 0))
     return ret;
 
-  ret = initialize_cpuset_subsystem (cgroup_path, err);
+  ret = initialize_cpuset_subsystem_resources (cgroup_path, err, resources);
   if (UNLIKELY (ret < 0))
     return ret;