engines: pvsync2 libaio io_uring: add support for RWF_NOWAIT

[fio.git] / fio.1

diff --git a/fio.1 b/fio.1
index 47bc15920831804ed3bba30ddc42685889f6d785..f469c46ed798f8521e6747e461a0625853a0c3e4 100644 (file)
--- a/fio.1
+++ b/fio.1
@@ -1857,6 +1857,22 @@ than normal.
 When hipri is set this determines the probability of a pvsync2 I/O being high
 priority. The default is 100%.
 .TP
+.BI (pvsync2,libaio,io_uring)nowait
+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 \fBignore_error\fR=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.
+.TP
 .BI (cpuio)cpuload \fR=\fPint
 Attempt to use the specified percentage of CPU cycles. This is a mandatory
 option when using cpuio I/O engine.