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) or epoll_create1(2).

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);