Update man page clarifying the usage of rw_sequencer=sequential Added few examples explaining the offset generation for rw_sequencer. Fixes: https://github.com/axboe/fio/issues/1223 Signed-off-by: Ankit Kumar <ankit.kumar@xxxxxxxxxxx> --- HOWTO.rst | 35 ++++++++++++++++++++++++++++------- fio.1 | 47 +++++++++++++++++++++++++++++++++++++++++------ 2 files changed, 69 insertions(+), 13 deletions(-) diff --git a/HOWTO.rst b/HOWTO.rst index 0a48a453..17caaf5d 100644 --- a/HOWTO.rst +++ b/HOWTO.rst @@ -1176,13 +1176,34 @@ I/O type Generate the same offset. ``sequential`` is only useful for random I/O, where fio would normally - generate a new random offset for every I/O. If you append e.g. 8 to randread, - you would get a new random offset for every 8 I/Os. The result would be a - seek for only every 8 I/Os, instead of for every I/O. Use ``rw=randread:8`` - to specify that. As sequential I/O is already sequential, setting - ``sequential`` for that would not result in any differences. ``identical`` - behaves in a similar fashion, except it sends the same offset 8 number of - times before generating a new offset. + generate a new random offset for every I/O. If you append e.g. 8 to + randread, i.e. ``rw=randread:8`` you would get a new random offset for + every 8 I/Os. The result would be a sequence of 8 sequential offsets + with a random starting point. However this behavior may change if a + sequential I/O reaches end of the file. As sequential I/O is already + sequential, setting ``sequential`` for that would not result in any + difference. ``identical`` behaves in a similar fashion, except it sends + the same offset 8 number of times before generating a new offset. + + Example #1:: + + rw=randread:8 + rw_sequencer=sequential + bs=4k + + The generated sequence of offsets will look like this: + 4k, 8k, 12k, 16k, 20k, 24k, 28k, 32k, 92k, 96k, 100k, 104k, 108k, + 112k, 116k, 120k, 48k, 52k ... + + Example #2:: + + rw=randread:8 + rw_sequencer=identical + bs=4k + + The generated sequence of offsets will look like this: + 4k, 4k, 4k, 4k, 4k, 4k, 4k, 4k, 92k, 92k, 92k, 92k, 92k, 92k, 92k, 92k, + 48k, 48k, 48k ... .. option:: unified_rw_reporting=str diff --git a/fio.1 b/fio.1 index eb87533f..527b3d46 100644 --- a/fio.1 +++ b/fio.1 @@ -952,12 +952,47 @@ Generate the same offset. .P \fBsequential\fR is only useful for random I/O, where fio would normally generate a new random offset for every I/O. If you append e.g. 8 to randread, -you would get a new random offset for every 8 I/Os. The result would be a -seek for only every 8 I/Os, instead of for every I/O. Use `rw=randread:8' -to specify that. As sequential I/O is already sequential, setting -\fBsequential\fR for that would not result in any differences. \fBidentical\fR -behaves in a similar fashion, except it sends the same offset 8 number of -times before generating a new offset. +i.e. `rw=randread:8' you would get a new random offset for every 8 I/Os. The +result would be a sequence of 8 sequential offsets with a random starting +point. However this behavior may change if a sequential I/O reaches end of the +file. As sequential I/O is already sequential, setting \fBsequential\fR for +that would not result in any difference. \fBidentical\fR behaves in a similar +fashion, except it sends the same offset 8 number of times before generating a +new offset. +.P +.P +Example #1: +.RS +.P +.PD 0 +rw=randread:8 +.P +rw_sequencer=sequential +.P +bs=4k +.PD +.RE +.P +The generated sequence of offsets will look like this: +4k, 8k, 12k, 16k, 20k, 24k, 28k, 32k, 92k, 96k, 100k, 104k, 108k, 112k, 116k, +120k, 48k, 52k ... +.P +.P +Example #2: +.RS +.P +.PD 0 +rw=randread:8 +.P +rw_sequencer=identical +.P +bs=4k +.PD +.RE +.P +The generated sequence of offsets will look like this: +4k, 4k, 4k, 4k, 4k, 4k, 4k, 4k, 92k, 92k, 92k, 92k, 92k, 92k, 92k, 92k, 48k, +48k, 48k ... .RE .TP .BI unified_rw_reporting \fR=\fPstr -- 2.17.1
