lib.numa: gracefully handle failure to read CPU performance governor

src/lib/numa.lua

@@ -158,12 +158,20 @@ local function assert_irqbalanced_disabled (warn)
  end
 end
 
+local function read_cpu_performance_governor (cpu)
+ local path = '/sys/devices/system/cpu/cpu'..cpu..'/cpufreq/scaling_governor'
+ local f = io.open(path)
+ if not f then return "unknown" end
+ local gov = f:read()
+ f:close()
+ return gov
+end
+
 local function check_cpu_performance_tuning (cpu, strict)
  local warn = warn
  if strict then warn = die end
  assert_irqbalanced_disabled(warn)
- local path = '/sys/devices/system/cpu/cpu'..cpu..'/cpufreq/scaling_governor'
- local gov = assert(io.open(path)):read()
+ local gov = read_cpu_performance_governor(cpu)
  if not gov:match('performance') then
  warn('Expected performance scaling governor for CPU %s, but got "%s"',
  cpu, gov)