gfio: display slat, clat, and lat percentiles

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 41d32c04dc638b12de1dc20e9444ed4462c81051..f19f9226a93de504d04aad6c60c27856bf1b19cb 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -1996,6 +1996,11 @@ I/O engine
                        set  `filesize` so that all the accounting still occurs, but no
                        actual I/O will be done other than creating the file.
 
+               **filestat**
+                       Simply do stat() and do no I/O to the file. You need to set 'filesize'
+                       and 'nrfiles', so that files will be created.
+                       This engine is to measure file lookup and meta data access.
+
                **libpmem**
                        Read and write using mmap I/O to a file on a filesystem
                        mounted with DAX on a persistent memory device through the PMDK
@@ -2029,21 +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]
 
@@ -2248,6 +2261,10 @@ with the caveat that when used on the command line, they must come after the
        multiple paths exist between the client and the server or in certain loopback
        configurations.
 
+.. option:: lstat=bool : [filestat]
+
+       Use lstat(2) to measure lookup/getattr performance. Default is 0.
+
 .. option:: readfua=bool : [sg]
 
        With readfua option set to 1, read operations include
@@ -2687,11 +2704,15 @@ 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