Vadim Lobanov <[email protected]> wrote:
>
> Patch to provide some microoptimizations for the poll() system call
> implementation. The loop that traverses over the "struct pollfd" entries
> was moved from do_pollfd() to its single caller do_poll(), so that
> do_pollfd() no longer mucks around with the "count" and the "pt"
> variables that should belong to do_poll() alone. This saves unnecessary
> levels of indirection. Modifications were run tested.
>
>
> 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 2006-04-13 18:54:14.000000000 -0700
> @@ -544,37 +544,30 @@ 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)
> +static int do_pollfd(struct pollfd * pollfd, poll_table * pwait)
Please omit the space after the asterisk:
static int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
because it doesn't impart any information, it is sightly misleading, it
wastes screen real-estate and we should be consistent.
> {
> - 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 &= pollfd->events | POLLERR | POLLHUP;
> + fput_light(file, fput_needed);
> }
> - fdp->revents = mask;
> }
> + pollfd->revents = mask;
> +
> + return (mask != 0);
> }
So do_poll_fd() returns either 0 or 1.
> static int do_poll(unsigned int nfds, struct poll_list *list,
> @@ -592,10 +585,19 @@ 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++) {
> + int ev;
> +
> + ev = do_pollfd(pfd, pt);
`ev' is either 0 or 1.
> + count += ev;
> + ev--;
`ev' is either -1 or 0.
> + pt = (poll_table*)((unsigned long)pt & ev);
So as long as the sign-extension works as we hope (which I think it will),
`pt' is either unaltered or is NULL.
Yuk. Sorry, no.
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