Poll cleanup and microoptimization patch.
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: Vadim Lobanov <[email protected]>
diff -Npru linux-2.6.17-rc1/fs/select.c linux-new/fs/select.c
--- linux-2.6.17-rc1/fs/select.c 2006-04-12 20:31:54.000000000 -0700
+++ linux-new/fs/select.c 2006-04-14 19:12:37.000000000 -0700
@@ -544,37 +544,38 @@ 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;
+ unsigned int mask;
+ int fd;
- for (i = 0; i < num; i++) {
- int fd;
- unsigned int mask;
- struct pollfd *fdp;
-
- mask = 0;
- fdp = fdpage+i;
- fd = fdp->fd;
- if (fd >= 0) {
- int fput_needed;
- struct 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;
- fput_light(file, fput_needed);
- }
- if (mask) {
- *pwait = NULL;
- (*count)++;
- }
+ mask = 0;
+ fd = pollfd->fd;
+ if (fd >= 0) {
+ int 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 out unneeded events. */
+ mask &= pollfd->events | POLLERR | POLLHUP;
+ fput_light(file, fput_needed);
}
- fdp->revents = mask;
}
+ pollfd->revents = mask;
+
+ return mask;
}
static int do_poll(unsigned int nfds, struct poll_list *list,
@@ -592,11 +593,29 @@ static int do_poll(unsigned int nfds, s
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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