ioctl_eventpoll(2)            System Calls Manual           ioctl_eventpoll(2)

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);

SEE ALSO
       ioctl(2), epoll_create(2), epoll_create1(2), epoll(7)

       linux.git/Documentation/networking/napi.rst

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

Linux man-pages 6.9.1             2024-06-17                ioctl_eventpoll(2)