[PATCH] Poll cleanups/microoptimizations
Vadim Lobanov [Fri, 23 Jun 2006 09:05:16 +0000 (02:05 -0700)]
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 <vlobanov@speakeasy.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/select.c

index a8109ba..9c4f0f2 100644 (file)
@@ -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;
-
-               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)++;
-                       }
+       unsigned int mask;
+       int fd;
+
+       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,
@@ -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;