Re: [lkp-robot] [fs] 3deb642f0d: will-it-scale.per_process_ops -8.8% regression

Christoph Hellwig
2018-06-22T09:50:53Z

And a version with select() also covered:

---
From 317159003ae28113cf759c632b161fb39192fe3c Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Fri, 22 Jun 2018 11:36:26 +0200
Subject: fs: optimize away ->_qproc indirection for poll_mask based polling

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/select.c | 38 +++++++++++++++++++++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/fs/select.c b/fs/select.c
index bc3cc0f98896..2c9d81892509 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -528,6 +528,24 @@ static int do_select(int n, fd_set_bits *fds, struct timespec64 *end_time)
wait_key_set(wait, in, out, bit,
busy_flag);
mask = vfs_poll(f.file, wait);
+ if (f.file->f_op->poll) {
+ mask = f.file->f_op->poll(f.file, wait);
+ } else if (file_has_poll_mask(f.file)) {
+ struct wait_queue_head *head;
+
+ head = f.file->f_op->get_poll_head(f.file, wait->_key);
+ if (!head) {
+ mask = DEFAULT_POLLMASK;
+ } else if (IS_ERR(head)) {
+ mask = EPOLLERR;
+ } else {
+ if (wait->_qproc)
+ __pollwait(f.file, head, wait);
+ mask = f.file->f_op->poll_mask(f.file, wait->_key);
+ }
+ } else {
+ mask = DEFAULT_POLLMASK;
+ }

fdput(f);
if ((mask & POLLIN_SET) && (in & bit)) {
@@ -845,7 +863,25 @@ static inline __poll_t do_pollfd(struct pollfd *pollfd, poll_table *pwait,
/* userland u16 ->events contains POLL... bitmap */
filter = demangle_poll(pollfd->events) | EPOLLERR | EPOLLHUP;
pwait->_key = filter | busy_flag;
- mask = vfs_poll(f.file, pwait);
+ if (f.file->f_op->poll) {
+ mask = f.file->f_op->poll(f.file, pwait);
+ } else if (file_has_poll_mask(f.file)) {
+ struct wait_queue_head *head;
+
+ head = f.file->f_op->get_poll_head(f.file, pwait->_key);
+ if (!head) {
+ mask = DEFAULT_POLLMASK;
+ } else if (IS_ERR(head)) {
+ mask = EPOLLERR;
+ } else {
+ if (pwait->_qproc)
+ __pollwait(f.file, head, pwait);
+ mask = f.file->f_op->poll_mask(f.file, pwait->_key);
+ }
+ } else {
+ mask = DEFAULT_POLLMASK;
+ }
+
if (mask & busy_flag)
*can_busy_poll = true;
mask &= filter; /* Mask out unneeded events. */
--
2.17.1