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diff --git a/HOWTO b/HOWTO
index e5b09fd6..745e9c72 100644
--- a/HOWTO
+++ b/HOWTO
@@ -108,8 +108,8 @@ to use any ascii name you want, except 'global' which has special meaning.
 A global section sets defaults for the jobs described in that file. A job
 may override a global section parameter, and a job file may even have
 several global sections if so desired. A job is only affected by a global
-section residing above it. If the first character in a line is a ';', the
-entire line is discarded as a comment.
+section residing above it. If the first character in a line is a ';' or a
+'#', the entire line is discarded as a comment.
 
 So lets look at a really simple job file that define to threads, each
 randomly reading from a 128MiB file.
@@ -289,11 +289,27 @@ ioengine=str	Defines how the job issues io to the file. The following
 				or receive, if the latter only the port
 				argument is used.
 
+			external Prefix to specify loading an external
+				IO engine object file. Append the engine
+				filename, eg ioengine=external:/tmp/foo.o
+				to load ioengine foo.o in /tmp.
+
 iodepth=int	This defines how many io units to keep in flight against
 		the file. The default is 1 for each file defined in this
 		job, can be overridden with a larger value for higher
 		concurrency.
 
+iodepth_batch=int This defines how many pieces of IO to submit at once.
+		It defaults to the same as iodepth, but can be set lower
+		if one so desires.
+
+iodepth_low=int	The low water mark indicating when to start filling
+		the queue again. Defaults to the same as iodepth, meaning
+		that fio will attempt to keep the queue full at all times.
+		If iodepth is set to eg 16 and iodepth_low is set to 4, then
+		after fio has filled the queue of 16 requests, it will let
+		the depth drain down to 4 before starting to fill it again.
+
 direct=bool	If value is true, use non-buffered io. This is usually
 		O_DIRECT.
 
@@ -343,7 +359,14 @@ prioclass=int	Set the io priority class. See man ionice(1).
 
 thinktime=int	Stall the job x microseconds after an io has completed before
 		issuing the next. May be used to simulate processing being
-		done by an application. See thinktime_blocks.
+		done by an application. See thinktime_blocks and
+		thinktime_spin.
+
+thinktime_spin=int
+		Only valid if thinktime is set - pretend to spend CPU time
+		doing something with the data received, before falling back
+		to sleeping for the rest of the period specified by
+		thinktime.
 
 thinktime_blocks
 		Only valid if thinktime is set - control how many blocks
@@ -556,6 +579,8 @@ Client1 (g=0): err= 0:
     bw (KiB/s) : min=    0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
   cpu        : usr=1.49%, sys=0.25%, ctx=7969
   IO depths    : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
+     lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
+     lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
 
 The client number is printed, along with the group id and error of that
 thread. Below is the io statistics, here for writes. In the order listed,
@@ -585,6 +610,12 @@ IO depths=	The distribution of io depths over the job life time. The
 		16= entries includes depths up to that value but higher
 		than the previous entry. In other words, it covers the
 		range from 16 to 31.
+IO latencies=	The distribution of IO completion latencies. This is the
+		time from when IO leaves fio and when it gets completed.
+		The numbers follow the same pattern as the IO depths,
+		meaning that 2=1.6% means that 1.6% of the IO completed
+		within 2 msecs, 20=12.8% means that 12.8% of the IO
+		took more than 10 msecs, but less than (or equal to) 20 msecs.
 
 After each client has been listed, the group statistics are printed. They
 will look like this: