[RFC PATCH 05/21] pipe: Conditionalise wakeup in pipe_read()

[David Howells]

Only do a wakeup in pipe_read() if we made space in a completely full
buffer.  The producer shouldn't be waiting on pipe->wait otherwise.

Signed-off-by: David Howells <dhowe...@redhat.com>
---

 fs/pipe.c |   15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 08af7e7bbea2..0d25cb090a03 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -327,11 +327,13 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
                                spin_lock_irq(&pipe->wait.lock);
                                tail++;
                                pipe_commit_read(pipe, tail);
-                               do_wakeup = 0;
-                               prelocked_wake_up_interruptible_sync_poll(
-                                       &pipe->wait, EPOLLOUT | EPOLLWRNORM);
+                               do_wakeup = 1;
+                               if (head - (tail - 1) == pipe->max_usage)
+                                       
prelocked_wake_up_interruptible_sync_poll(
+                                               &pipe->wait, EPOLLOUT | 
EPOLLWRNORM);
                                spin_unlock_irq(&pipe->wait.lock);
-                               kill_fasync(&pipe->fasync_writers, SIGIO, 
POLL_OUT);
+                               if (head - (tail - 1) == pipe->max_usage)
+                                       kill_fasync(&pipe->fasync_writers, 
SIGIO, POLL_OUT);
                        }
                        total_len -= chars;
                        if (!total_len)
@@ -360,11 +362,6 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
                                ret = -ERESTARTSYS;
                        break;
                }
-               if (do_wakeup) {
-                       wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | 
EPOLLWRNORM);
-                       kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
-                       do_wakeup = 0;
-               }
                pipe_wait(pipe);
        }
        __pipe_unlock(pipe);