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