core: always enable CPU accounting; cgtop: drop cgv1 handling (#37448)

src/basic/cgroup-util.c

@@ -2181,57 +2181,6 @@ static const char *const cgroup_controller_table[_CGROUP_CONTROLLER_MAX] = {
 
 DEFINE_STRING_TABLE_LOOKUP(cgroup_controller, CGroupController);
 
-CGroupMask get_cpu_accounting_mask(void) {
-        static CGroupMask needed_mask = (CGroupMask) -1;
-
-        /* On kernel ≥4.15 with unified hierarchy, cpu.stat's usage_usec is
-         * provided externally from the CPU controller, which means we don't
-         * need to enable the CPU controller just to get metrics. This is good,
-         * because enabling the CPU controller comes at a minor performance
-         * hit, especially when it's propagated deep into large hierarchies.
-         * There's also no separate CPU accounting controller available within
-         * a unified hierarchy.
-         *
-         * This combination of factors results in the desired cgroup mask to
-         * enable for CPU accounting varying as follows:
-         *
-         *                   ╔═════════════════════╤═════════════════════╗
-         *                   ║     Linux ≥4.15     │     Linux <4.15     ║
-         *   ╔═══════════════╬═════════════════════╪═════════════════════╣
-         *   ║ Unified       ║ nothing             │ CGROUP_MASK_CPU     ║
-         *   ╟───────────────╫─────────────────────┼─────────────────────╢
-         *   ║ Hybrid/Legacy ║ CGROUP_MASK_CPUACCT │ CGROUP_MASK_CPUACCT ║
-         *   ╚═══════════════╩═════════════════════╧═════════════════════╝
-         *
-         * We check kernel version here instead of manually checking whether
-         * cpu.stat is present for every cgroup, as that check in itself would
-         * already be fairly expensive.
-         *
-         * Kernels where this patch has been backported will therefore have the
-         * CPU controller enabled unnecessarily. This is more expensive than
-         * necessary, but harmless. ☺️
-         */
-
-        if (needed_mask == (CGroupMask) -1) {
-                if (cg_all_unified()) {
-                        struct utsname u;
-                        assert_se(uname(&u) >= 0);
-
-                        if (strverscmp_improved(u.release, "4.15") < 0)
-                                needed_mask = CGROUP_MASK_CPU;
-                        else
-                                needed_mask = 0;
-                } else
-                        needed_mask = CGROUP_MASK_CPUACCT;
-        }
-
-        return needed_mask;
-}
-
-bool cpu_accounting_is_cheap(void) {
-        return get_cpu_accounting_mask() == 0;
-}
-
 static const char* const managed_oom_mode_table[_MANAGED_OOM_MODE_MAX] = {
         [MANAGED_OOM_AUTO] = "auto",
         [MANAGED_OOM_KILL] = "kill",

src/basic/cgroup-util.h

@@ -86,9 +86,6 @@ static inline CGroupMask CGROUP_MASK_EXTEND_JOINED(CGroupMask mask) {
         return mask;
 }
 
-CGroupMask get_cpu_accounting_mask(void);
-bool cpu_accounting_is_cheap(void);
-
 /* Special values for all weight knobs on unified hierarchy */
 #define CGROUP_WEIGHT_INVALID UINT64_MAX
 #define CGROUP_WEIGHT_IDLE UINT64_C(0)