Commit 4a4b69f7 authored by Vadim Lobanov's avatar Vadim Lobanov Committed by Linus Torvalds
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[PATCH] Poll cleanups/microoptimizations 



The "count" and "pt" variables are declared and modified by do_poll(), as
well as accessed and written indirectly in the do_pollfd() subroutine.

This patch pulls all handling of these variables into the do_poll()
function, thereby eliminating the odd use of indirection in do_pollfd().
This is done by pulling the "struct pollfd" traversal loop from do_pollfd()
into its only caller do_poll().  As an added bonus, the patch saves a few
clock cycles, and also adds comments to make the code easier to follow.

Signed-off-by: default avatarVadim Lobanov <vlobanov@speakeasy.net>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2da13264

fs/select.c

+51 −32
Original line number Diff line number Diff line
@@ -546,37 +546,38 @@ struct poll_list { 


#define POLLFD_PER_PAGE  ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))



static void do_pollfd(unsigned int num, struct pollfd * fdpage,

	poll_table ** pwait, int *count)

/*

 * Fish for pollable events on the pollfd->fd file descriptor. We're only

 * interested in events matching the pollfd->events mask, and the result

 * matching that mask is both recorded in pollfd->revents and returned. The

 * pwait poll_table will be used by the fd-provided poll handler for waiting,

 * if non-NULL.

 */

static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)

{

	int i;



	for (i = 0; i < num; i++) {

		int fd;

	unsigned int mask;

		struct pollfd *fdp;

	int fd;



	mask = 0;

		fdp = fdpage+i;

		fd = fdp->fd;

	fd = pollfd->fd;

	if (fd >= 0) {

		int fput_needed;

			struct file * file = fget_light(fd, &fput_needed);

		struct file * file;



		file = fget_light(fd, &fput_needed);

		mask = POLLNVAL;

		if (file != NULL) {

			mask = DEFAULT_POLLMASK;

			if (file->f_op && file->f_op->poll)

					mask = file->f_op->poll(file, *pwait);

				mask &= fdp->events | POLLERR | POLLHUP;

				mask = file->f_op->poll(file, pwait);

			/* Mask out unneeded events. */

			mask &= pollfd->events | POLLERR | POLLHUP;

			fput_light(file, fput_needed);

		}

			if (mask) {

				*pwait = NULL;

				(*count)++;

			}

		}

		fdp->revents = mask;

	}

	pollfd->revents = mask;



	return mask;

}



static int do_poll(unsigned int nfds,  struct poll_list *list,
@@ -594,11 +595,29 @@ static int do_poll(unsigned int nfds, struct poll_list *list, 
		long __timeout;



		set_current_state(TASK_INTERRUPTIBLE);

		walk = list;

		while(walk != NULL) {

			do_pollfd( walk->len, walk->entries, &pt, &count);

			walk = walk->next;

		for (walk = list; walk != NULL; walk = walk->next) {

			struct pollfd * pfd, * pfd_end;



			pfd = walk->entries;

			pfd_end = pfd + walk->len;

			for (; pfd != pfd_end; pfd++) {

				/*

				 * Fish for events. If we found one, record it

				 * and kill the poll_table, so we don't

				 * needlessly register any other waiters after

				 * this. They'll get immediately deregistered

				 * when we break out and return.

				 */

				if (do_pollfd(pfd, pt)) {

					count++;

					pt = NULL;

				}

			}

		}

		/*

		 * All waiters have already been registered, so don't provide

		 * a poll_table to them on the next loop iteration.

		 */

		pt = NULL;

		if (count || !*timeout || signal_pending(current))

			break;

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