On 06/17, Mateusz Guzik wrote:
>
> There are trivial touch ups which can be done by adding a bunch of
> predicts and inlining kill_fasync if someone can be bothered.
Speaking of trivial touch ups...
anon_pipe_write() does:
* Epoll nonsensically wants a wakeup whether the pipe
* was already empty or not.
*/
if (was_empty || pipe->poll_usage)
wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN |
EPOLLRDNORM);
Again, I have no idea if the unnecessary wakeup affects the performance,
probably not. But somehow this "|| poll_usage" condition looks annoying
to me...
Perhaps it makes sense to change pipe_poll() to not set ->poll_usage
unconditionally?
Oleg.
---
diff --git a/fs/pipe.c b/fs/pipe.c
index 429b0714ec57..a60be1b71eb7 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -760,10 +760,12 @@ pipe_poll(struct file *filp, poll_table *wait)
struct pipe_inode_info *pipe = filp->private_data;
union pipe_index idx;
+#ifdef CONFIG_EPOLL
/* Epoll has some historical nasty semantics, this enables them */
- if (unlikely(!READ_ONCE(pipe->poll_usage)))
+ if ((filp->f_mode & FMODE_READ) && filp->f_ep
+ && unlikely(!READ_ONCE(pipe->poll_usage)))
WRITE_ONCE(pipe->poll_usage, true);
-
+#endif
/*
* Reading pipe state only -- no need for acquiring the semaphore.
*
