X-Git-Url: https://git.kernel.dk/?p=fio.git;a=blobdiff_plain;f=HOWTO;h=06408e40e16a91fadeea2dce399efc444845b6e5;hp=8e6e29bbc7dd98e6eb9857596c02de03ebdd0635;hb=5af1c6f3b46b40ef6b7021a34fd38889226e137f;hpb=48097d5c61aa1718e6dd4b3b647ea2eb6f00fcfb

diff --git a/HOWTO b/HOWTO
index 8e6e29bb..06408e40 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.
@@ -253,6 +253,14 @@ bs_unaligned	If this option is given, any byte size value within bsrange
 
 nrfiles=int	Number of files to use for this job. Defaults to 1.
 
+file_service_type=str  Defines how fio decides which file from a job to
+		service next. The following types are defined:
+
+			random	Just choose a file at random.
+
+			roundrobin  Round robin over open files. This
+				is the default.
+
 ioengine=str	Defines how the job issues io to the file. The following
 		types are defined:
 
@@ -289,11 +297,27 @@ 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.
 
@@ -563,8 +587,8 @@ 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%, 8=3.2%, 16=12.8%, 32=38.4%, 64=24.8%, 128=15.2%
-     lat (msec): 256=4.0%, 512=0.0%, 1024=0.0%, >=2048=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,
@@ -598,8 +622,8 @@ 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, 16=12.8% means that 12.8% of the IO
-		took more than 8 msecs, but less than (or equal to) 16 msecs.
+		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: