Add kb_base option to specify the base unit of a kilobyte

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 2d155aa..6cdd71d 100644
--- a/HOWTO
+++ b/HOWTO
@@ -290,6 +290,11 @@
 		IO's, instead of for every IO. Use rw=randread:8 to specify
 		that.
 
+kb_base=int	The base unit for a kilobyte. The defacto base is 2^10, 1024.
+		Storage manufacturers like to use 10^3 or 1000 as a base
+		ten unit instead, for obvious reasons. Allow values are
+		1024 or 1000, with 1024 being the default.
+
 randrepeat=bool	For random IO workloads, seed the generator in a predictable
 		way so that results are repeatable across repetitions.