1 files changed, 21 insertions, 7 deletions
diff --git a/lib/data.lua b/lib/data.lua
index acf7a0f..2047ef8 100644
--- a/lib/data.lua
+++ b/lib/data.lua
@@ -62,14 +62,28 @@ end
 -- Globbing by name, never by a fixed hwmon index: indices drift across kernel
 -- and hardware reorders, and a stale index silently reports a different chip.
 -- Carried over from the previous conky config, where this was the hard-won bit.
+--
+-- The result is memoized per chip name, hits and misses alike. A chip's hwmon
+-- directory is stable for the process's life, and the draw hook calls this
+-- several times per frame: without the cache every sensor read popens grep,
+-- which is exactly the subprocess-per-draw the samplers exist to avoid. A miss
+-- is cached too, so an absent chip is not re-globbed on every frame.
+local hwmon_cache = {}
+
 function M.hwmon_dir(name)
-  local p = io.popen('grep -lx ' .. ("%q"):format(name)
-    .. ' /sys/class/hwmon/hwmon*/name 2>/dev/null')
-  if not p then return nil end
-  local hit = p:read('*l')
-  p:close()
-  if not hit then return nil end
-  return hit:match('^(.*)/name$')
+  if type(name) ~= 'string' then return nil end
+  if hwmon_cache[name] == nil then
+    local p = io.popen('grep -lx ' .. ("%q"):format(name)
+      .. ' /sys/class/hwmon/hwmon*/name 2>/dev/null')
+    local dir = false
+    if p then
+      local hit = p:read('*l')
+      p:close()
+      if hit then dir = hit:match('^(.*)/name$') end
+    end
+    hwmon_cache[name] = dir
+  end
+  return hwmon_cache[name] or nil
 end
 
 -- A stateful CPU-load counter.