doc: add iodepth_batch_complete_omit option

Introduce the effect and scenes of the option.

Signed-off-by: Fanghao Sha <[email protected]>

Author: lausaa

HOWTO.rst

@@ -2890,6 +2890,19 @@ I/O depth
 	if none of I/O has been completed yet, we will NOT wait and immediately exit
 	the system call. In this example we simply do polling.
 
+.. option:: iodepth_batch_complete_omit=int
+
+	The number of in-flight IOs that need not be retrieved on quiescing. It
+	defaults to 0 which means all in-flight IOs will be retrieved until completion
+	as not to skew the latency. After that, if in the rate-limiting context, the
+	next IO will be set after a fixed delay. But in some cases, the in-flight IOs
+	may need be hanging for a while to merge more subseqeuent IOs in order to get
+	a better bandwidth or reach the EC stripe length, and so on. And the hanging
+	time may delay the next IO for long if all in-flight IOs must be retrieved.
+	Therefore, this option will be used to skip quiescing partially(IOs in merge
+	waiting) for a smooth data flow, and as such, it is not suitable for the
+	latency-sensitive scenarios.
+
 .. option:: iodepth_low=int
 
 	The low water mark indicating when to start filling the queue

fio.1

@@ -2650,6 +2650,18 @@ if none of I/O has been completed yet, we will NOT wait and immediately exit
 the system call. In this example we simply do polling.
 .RE
 .TP
+.BI iodepth_batch_complete_omit \fR=\fPint
+The number of in-flight IOs that need not be retrieved on quiescing. It
+defaults to 0 which means all in-flight IOs will be retrieved until completion
+as not to skew the latency. After that, if in the rate-limiting context, the
+next IO will be set after a fixed delay. But in some cases, the in-flight IOs
+may need be hanging for a while to merge more subseqeuent IOs in order to get
+a better bandwidth or reach the EC stripe length, and so on. And the hanging
+time may delay the next IO for long if all in-flight IOs must be retrieved.
+Therefore, this option will be used to skip quiescing partially(IOs in merge
+waiting) for a smooth data flow, and as such, it is not suitable for the
+latency-sensitive scenarios.
+.TP
 .BI iodepth_low \fR=\fPint
 The low water mark indicating when to start filling the queue
 again. Defaults to the same as \fBiodepth\fR, meaning that fio will