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.\" Copyright (C) 2025 Jens Axboe <axboe@kernel.dk>
.\" Copyright (C) 2025 Ammar Faizi <ammarfaizi2@gnuweeb.org>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_set_iowait 3 "July 27, 2025" "liburing-2.12" "liburing Manual"
.SH NAME
io_uring_set_iowait \- toggle of iowait usage when waiting on CQEs
.SH SYNOPSIS
.nf
.B #include <liburing.h>
.PP
.BI "int io_uring_set_iowait(struct io_uring *" ring ",
.BI " bool " enable_iowait ");"
.fi
.SH DESCRIPTION
.PP
By default, io_uring marks a waiting task as being in iowait if it's
sleeping waiting on events and there are pending requests. This isn't
necessarily always useful, and may be confusing on non-storage setups
where iowait isn't expected. It can also cause extra power usage by
preventing the CPU from entering lower sleep states.
The
.BR io_uring_set_iowait (3)
function allows the user to toggle this behavior. If
.BI enable_iowait
is set to true, the iowait behavior is enabled. If it is set to false,
the iowait behavior is disabled. The iowait behavior is enabled by
default when a ring is created.
If the iowait is disabled, the submit functions will set
.B IORING_ENTER_NO_IOWAIT
in the
.BI flags
argument to
.BR io_uring_enter (2).
If the kernel supports this feature, it will be marked by having
the
.B IORING_FEAT_NO_IOWAIT
feature flag set.
Available since kernel 6.15.
.SH RETURN VALUE
On success,
.BR io_uring_set_iowait (3)
returns 0. On failure, it returns
.BR -EOPNOTSUPP .
.SH SEE ALSO
.BR io_uring_enter (2),
.BR io_uring_submit (3),
.BR io_uring_submit_and_wait (3)
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