docs: mention unsupported configuration

It does not make sense when group_reporting is used for the constituent
jobs to have different values for options like unified_rw_reporting,
?lat_percentiles, etc. Mention that configurations with different values
for these parameters are unsupported.

Signed-off-by: Vincent Fu <[email protected]>

HOWTO.rst

@@ -4128,6 +4128,11 @@ Measurements and reporting
 	`job_start`. For these properties, the values for the first job are
 	recorded for the group.
 
+        Also, options like :option:`percentile_list` and
+        :option:`unified_rw_reporting` should be consistent among the jobs in a
+        reporting group. Having options like these vary across the jobs in a
+        reporting group is an unsupported configuration.
+
 .. option:: new_group
 
 	Start a new reporting group. See: :option:`group_reporting`.  If not given,
@@ -5391,4 +5396,8 @@ Terse output in client/server mode will differ slightly from what is produced
 when fio is run in stand-alone mode. See the terse output section for details.
 
 Also, if one fio invocation runs workloads on multiple servers, fio will
-provide at the end an aggregate summary report for all workloads.
+provide at the end an aggregate summary report for all workloads. This
+aggregate summary report assumes that options affecting reporting like
+:option:`unified_rw_reporting` and :option:`percentile_list` are identical
+across all the jobs summarized. Having different values for these options is an
+unsupported configuration.

fio.1

@@ -3844,6 +3844,10 @@ have a natural group-level equivalent. Examples include \fBkb_base\fR,
 \fBunit_base\fR, \fBsig_figs\fR, \fBthread_number\fR, \fBpid\fR, and
 \fBjob_start\fR. For these properties, the values for the first job are
 recorded for the group.
+.P
+Also, options like \fBpercentile_list\fR and \fBunified_rw_reporting\fR should
+be consistent among the jobs in a reporting group. Having options like these
+vary across the jobs in a reporting group is an unsupported configuration.
 .RE
 .TP
 .BI new_group
@@ -5148,7 +5152,11 @@ Terse output in client/server mode will differ slightly from what is produced
 when fio is run in stand-alone mode. See the terse output section for details.
 .P
 Also, if one fio invocation runs workloads on multiple servers, fio will
-provide at the end an aggregate summary report for all workloads.
+provide at the end an aggregate summary report for all workloads. This
+aggregate summary report assumes that options affecting reporting like
+\fBunified_rw_reporting\fR and \fBpercentile_list\fR are identical across all
+the jobs summarized. Having different values for these options is an
+unsupported configuration.
 .SH AUTHORS
 .B fio
 was written by Jens Axboe <[email protected]>.