chore: Add docs and move vars inside their if's

hooks/_common.sh

@@ -197,12 +197,12 @@ function common::is_hook_run_on_whole_repo {
 function common::get_cpu_num {
   local -r parallelism_ci_cpu_cores=$1
 
-  local cpu_quota cpu_period cpu_num
-  local millicpu
-
   if [[ -f /sys/fs/cgroup/cpu/cpu.cfs_quota_us &&
     ! -f /proc/sys/fs/binfmt_misc/WSLInterop ]]; then # WSL have cfs_quota_us, but WSL should be checked as usual Linux host
     # Inside K8s pod or DinD in K8s
+    local cpu_quota cpu_period cpu_num
+    # CPU quota should be calculated as `cpu.cfs_quota_us / cpu.cfs_period_us`
+    # See: https://docs.kernel.org/scheduler/sched-bwc.html
     cpu_quota=$(< /sys/fs/cgroup/cpu/cpu.cfs_quota_us)
     cpu_period=$(cat /sys/fs/cgroup/cpu/cpu.cfs_period_us 2> /dev/null || echo "$cpu_quota")
 
@@ -242,6 +242,7 @@ function common::get_cpu_num {
 
   if [[ -f /sys/fs/cgroup/cpu.max ]]; then
     # Inside Linux (Docker?) container
+    local millicpu
     millicpu=$(cut -d' ' -f1 /sys/fs/cgroup/cpu.max)
 
     if [[ $millicpu == max ]]; then