ioctl_eventpoll(2) - Linux manual page (original) (raw)

ioctleventpoll(2) System Calls Manual ioctleventpoll(2)

NAME top

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

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#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 top

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

   **EPIOCGPARAMS**
          Get the current _epollparams_ 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)](../man2/epoll%5Fcreate.2.html)
   or [epoll_create1(2)](../man2/epoll%5Fcreate1.2.html).

The epoll_params structure argp.busypollusecs 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.busypollbudget_ 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.preferbusypoll_ 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 top

   On success, 0 is returned.  On failure, -1 is returned, and _[errno](../man3/errno.3.html)_
   is set to indicate the error.

ERRORS top

   **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.busypollusecs_ exceeds **INT_MAX**.

   **EINVAL** _argp.preferbusypoll_ is not 0 or 1.

   **EPERM** The process is being run without **CAP_NET_ADMIN** and the
          specified _argp.busypollbudget_ exceeds **NAPI_POLL_WEIGHT**.

   **EFAULT** _argp_ is an invalid address.

STANDARDS top

   Linux.

HISTORY top

   Linux 6.9.  glibc 2.40.

EXAMPLES top

   /* 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);

COLOPHON top

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Linux man-pages 6.10 2024-07-23 ioctleventpoll(2)

Pages that refer to this page:epoll_create(2), epoll_ctl(2), ioctl(2), epoll(7)