diff --git a/profiles/throughput-performance/tuned.conf b/profiles/throughput-performance/tuned.conf
index 265ad2e..e15b4fc 100644
--- a/profiles/throughput-performance/tuned.conf
+++ b/profiles/throughput-performance/tuned.conf
@@ -11,6 +11,9 @@ energy_perf_bias=performance
 min_perf_pct=100
 
 [disk]
+# The default unit for readahead is KiB.  This can be adjusted to sectors
+# by specifying the relevant suffix, eg. (readahead => 8192 s). There must
+# be at least one space between the number and suffix (if suffix is specified).
 readahead=>4096
 
 [sysctl]