[PATCH v2] drm: make drm_file use keyed wakeups

From: Kenny Levinsen
Date: Fri Apr 24 2020 - 12:26:29 EST


Some processes, such as systemd, are only polling for EPOLLERR|EPOLLHUP.
As drm_file uses unkeyed wakeups, such a poll can receive many spurious
wakeups from uninteresting events if, for example, the file description
is subscribed to vblank events. This is the case with systemd, as it
polls a file description from logind that is shared with the users'
compositor.

Use keyed wakeups to allow the wakeup target to more efficiently discard
these uninteresting events.

Signed-off-by: Kenny Levinsen <kl@xxxxxx>
---
drivers/gpu/drm/drm_file.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index c4c704e01961..ec25b3d979d9 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -608,7 +608,8 @@ ssize_t drm_read(struct file *filp, char __user *buffer,
file_priv->event_space -= length;
list_add(&e->link, &file_priv->event_list);
spin_unlock_irq(&dev->event_lock);
- wake_up_interruptible(&file_priv->event_wait);
+ wake_up_interruptible_poll(&file_priv->event_wait,
+ EPOLLIN | EPOLLRDNORM);
break;
}

@@ -804,7 +805,8 @@ void drm_send_event_locked(struct drm_device *dev, struct drm_pending_event *e)
list_del(&e->pending_link);
list_add_tail(&e->link,
&e->file_priv->event_list);
- wake_up_interruptible(&e->file_priv->event_wait);
+ wake_up_interruptible_poll(&e->file_priv->event_wait,
+ EPOLLIN | EPOLLRDNORM);
}
EXPORT_SYMBOL(drm_send_event_locked);

--
2.26.1