---
name: "ioctl_eventpoll"
section: "2"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/ioctl_eventpoll"
---

# ioctl\_eventpoll(2)

ioctl() operations for epoll file descriptors

## NAME

ioctl\_eventpoll, EPIOCSPARAMS, EPIOCGPARAMS - ioctl() operations for epoll file descriptors

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <sys/epoll.h>  /* Definition of EPIOC* constants */
#include <sys/ioctl.h>
```

**int ioctl(int** *fd***, EPIOCSPARAMS, const struct epoll\_params \****argp***);** **int ioctl(int** *fd***, EPIOCGPARAMS, struct epoll\_params \****argp***);**

**#include \<sys/epoll.h\>**

```
struct epoll_params {
    uint32_t  busy_poll_usecs;   /* Number of usecs to busy poll */
    uint16_t  busy_poll_budget;  /* Max packets per poll */
    uint8_t   prefer_busy_poll;  /* Boolean preference  */
    /* pad the struct to a multiple of 64bits */
    uint8_t   __pad;             /* Must be zero */
};
```

## DESCRIPTION

- **EPIOCSPARAMS**

  Set the *epoll\_params* structure to configure the operation of epoll. Refer to the structure description below to learn what configuration is supported.

- **EPIOCGPARAMS**

  Get the current *epoll\_params* configuration settings.

All operations documented above must be performed on an epoll file descriptor, which can be obtained with a call to [**epoll\_create**(2)](/epoll_create/2.md) or [**epoll\_create1**(2)](/epoll_create1/2.md).

### The epoll\_params structure

*argp.busy\_poll\_usecs* denotes the number of microseconds that the network stack will busy poll. During this time period, the network device will be polled repeatedly for packets. This value cannot exceed **INT\_MAX**.

*argp.busy\_poll\_budget* denotes the maximum number of packets that the network stack will retrieve on each poll attempt. This value cannot exceed **NAPI\_POLL\_WEIGHT** (which is 64 as of Linux 6.9), unless the process is run with **CAP\_NET\_ADMIN**.

*argp.prefer\_busy\_poll* is a boolean field and must be either 0 (disabled) or 1 (enabled). If enabled, this indicates to the network stack that busy poll is the preferred method of processing network data and the network stack should give the application the opportunity to busy poll. Without this option, very busy systems may continue to do network processing via the normal method of IRQs triggering softIRQ and NAPI.

*argp.\_\_pad* must be zero.

## RETURN VALUE

On success, 0 is returned. On failure, -1 is returned, and *errno* is set to indicate the error.

## ERRORS

- **EOPNOTSUPP**

  The kernel was not compiled with busy poll support.

- **EINVAL**

  *fd* is not a valid file descriptor.

- **EINVAL**

  *argp.\_\_pad* is not zero.

- **EINVAL**

  *argp.busy\_poll\_usecs* exceeds **INT\_MAX**.

- **EINVAL**

  *argp.prefer\_busy\_poll* is not 0 or 1.

- **EPERM**

  The process is being run without **CAP\_NET\_ADMIN** and the specified *argp.busy\_poll\_budget* exceeds **NAPI\_POLL\_WEIGHT**.

- **EFAULT**

  *argp* is an invalid address.

## STANDARDS

Linux.

## HISTORY

Linux 6.9, glibc 2.40.

## EXAMPLES

```
/* Code to set the epoll params to enable busy polling */
int epollfd = epoll_create1(0);
struct epoll_params params;
if (epollfd == -1) {
    perror("epoll_create1");
    exit(EXIT_FAILURE);
}
memset(&params, 0, sizeof(struct epoll_params));
params.busy_poll_usecs = 25;
params.busy_poll_budget = 8;
params.prefer_busy_poll = 1;
if (ioctl(epollfd, EPIOCSPARAMS, &params) == -1) {
    perror("ioctl");
    exit(EXIT_FAILURE);
}
/* Code to show how to retrieve the current settings */
memset(&params, 0, sizeof(struct epoll_params));
if (ioctl(epollfd, EPIOCGPARAMS, &params) == -1) {
    perror("ioctl");
    exit(EXIT_FAILURE);
}
/* params struct now contains the current parameters */
fprintf(stderr, "epoll usecs: %lu\n", params.busy_poll_usecs);
fprintf(stderr, "epoll packet budget: %u\n", params.busy_poll_budget);
fprintf(stderr, "epoll prefer busy poll: %u\n", params.prefer_busy_poll);
```

## SEE ALSO

[**ioctl**(2)](/ioctl/2.md), [**epoll\_create**(2)](/epoll_create/2.md), [**epoll\_create1**(2)](/epoll_create1/2.md), [**epoll**(7)](/epoll/7.md)

*linux.git/Documentation/networking/napi.rst*

*linux.git/Documentation/admin-guide/sysctl/net.rst*