Merge branch 'priorityQueuing' of https://github.com/Seagate/fio

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 74318954b1fb73bc8d32a10c9c851da07def8466..0a3661684fb4653a1638b30e7d1e204abe6094a9 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -2034,21 +2034,29 @@ In addition, there are some parameters which are only valid when a specific
 with the caveat that when used on the command line, they must come after the
 :option:`ioengine` that defines them is selected.
 
-.. option:: hipri : [io_uring]
+.. option:: cmdprio_percentage=int : [io_uring] [libaio]
 
-       If this option is set, fio will attempt to use polled IO completions.
-       Normal IO completions generate interrupts to signal the completion of
-       IO, polled completions do not. Hence they are require active reaping
-       by the application. The benefits are more efficient IO for high IOPS
-       scenarios, and lower latencies for low queue depth IO.
+    Set the percentage of I/O that will be issued with higher priority by setting
+    the priority bit. Non-read I/O is likely unaffected by ``cmdprio_percentage``.
+    This option cannot be used with the `prio` or `prioclass` options. For this
+    option to set the priority bit properly, NCQ priority must be supported and
+    enabled and :option:`direct`\=1 option must be used.
 
 .. option:: fixedbufs : [io_uring]
 
-       If fio is asked to do direct IO, then Linux will map pages for each
-       IO call, and release them when IO is done. If this option is set, the
-       pages are pre-mapped before IO is started. This eliminates the need to
-       map and release for each IO. This is more efficient, and reduces the
-       IO latency as well.
+    If fio is asked to do direct IO, then Linux will map pages for each
+    IO call, and release them when IO is done. If this option is set, the
+    pages are pre-mapped before IO is started. This eliminates the need to
+    map and release for each IO. This is more efficient, and reduces the
+    IO latency as well.
+
+.. option:: hipri : [io_uring]
+
+    If this option is set, fio will attempt to use polled IO completions.
+    Normal IO completions generate interrupts to signal the completion of
+    IO, polled completions do not. Hence they are require active reaping
+    by the application. The benefits are more efficient IO for high IOPS
+    scenarios, and lower latencies for low queue depth IO.
 
 .. option:: registerfiles : [io_uring]
 
@@ -2692,11 +2700,15 @@ Threads, processes and job synchronization
        Set the I/O priority value of this job. Linux limits us to a positive value
        between 0 and 7, with 0 being the highest.  See man
        :manpage:`ionice(1)`. Refer to an appropriate manpage for other operating
-       systems since meaning of priority may differ.
+       systems since meaning of priority may differ. For per-command priority
+       setting, see I/O engine specific `cmdprio_percentage` and `hipri_percentage`
+       options.
 
 .. option:: prioclass=int
 
-       Set the I/O priority class. See man :manpage:`ionice(1)`.
+       Set the I/O priority class. See man :manpage:`ionice(1)`. For per-command
+       priority setting, see I/O engine specific `cmdprio_percentage` and
+       `hipri_percentage` options.
 
 .. option:: cpus_allowed=str