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From:   Kenny Levinsen <kl@kl.wtf>
To:     intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Cc:     daniel@ffwll.ch, airlied@linux.ie, tzimmermann@suse.de,
        mripard@kernel.org, maarten.lankhorst@linux.intel.com,
        linux-kernel@vger.kernel.org, Kenny Levinsen <kl@kl.wtf>
Subject: [PATCH v2] drm: make drm_file use keyed wakeups
Date:   Fri, 24 Apr 2020 18:26:15 +0200
Message-Id: <20200424162615.10461-1-kl@kl.wtf>
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Sender: linux-kernel-owner@vger.kernel.org
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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@kl.wtf>
---
 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