Enable error checking for the mutex that serializes overlapping I/O

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index cd6285524f392c0a911a2e133dd3d4b6b40aa371..8cf8d6506b219e0f9933813616a7d682218adb24 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -2097,6 +2097,26 @@ with the caveat that when used on the command line, they must come after the
        When hipri is set this determines the probability of a pvsync2 I/O being high
        priority. The default is 100%.
 
+.. option:: nowait : [pvsync2] [libaio] [io_uring]
+
+       By default if a request cannot be executed immediately (e.g. resource starvation,
+       waiting on locks) it is queued and the initiating process will be blocked until
+       the required resource becomes free.
+
+       This option sets the RWF_NOWAIT flag (supported from the 4.14 Linux kernel) and
+       the call will return instantly with EAGAIN or a partial result rather than waiting.
+
+       It is useful to also use ignore_error=EAGAIN when using this option.
+
+       Note: glibc 2.27, 2.28 have a bug in syscall wrappers preadv2, pwritev2.
+       They return EOPNOTSUP instead of EAGAIN.
+
+       For cached I/O, using this option usually means a request operates only with
+       cached data. Currently the RWF_NOWAIT flag does not supported for cached write.
+
+       For direct I/O, requests will only succeed if cache invalidation isn't required,
+       file blocks are fully allocated and the disk request could be issued immediately.
+
 .. option:: cpuload=int : [cpuio]
 
        Attempt to use the specified percentage of CPU cycles. This is a mandatory
@@ -2552,6 +2572,13 @@ I/O latency
        defaults to 100.0, meaning that all I/Os must be equal or below to the value
        set by :option:`latency_target`.
 
+.. option:: latency_run=bool
+
+       Used with :option:`latency_target`. If false (default), fio will find
+       the highest queue depth that meets :option:`latency_target` and exit. If
+       true, fio will continue running and try to meet :option:`latency_target`
+       by adjusting queue depth.
+
 .. option:: max_latency=time
 
        If set, fio will exit the job with an ETIMEDOUT error if it exceeds this
@@ -4138,7 +4165,7 @@ Fio supports a variety of log file formats, for logging latencies, bandwidth,
 and IOPS. The logs share a common format, which looks like this:
 
     *time* (`msec`), *value*, *data direction*, *block size* (`bytes`),
-    *offset* (`bytes`)
+    *offset* (`bytes`), *command priority*
 
 *Time* for the log entry is always in milliseconds. The *value* logged depends
 on the type of log, it will be one of the following:
@@ -4163,6 +4190,9 @@ The entry's *block size* is always in bytes. The *offset* is the position in byt
 from the start of the file for that particular I/O. The logging of the offset can be
 toggled with :option:`log_offset`.
 
+*Command priority* is 0 for normal priority and 1 for high priority. This is controlled
+by the ioengine specific :option:`cmdprio_percentage`.
+
 Fio defaults to logging every individual I/O but when windowed logging is set
 through :option:`log_avg_msec`, either the average (by default) or the maximum
 (:option:`log_max_value` is set) *value* seen over the specified period of time