linux-kernel - Re: [PATCH v2] drm: make drm

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Date:   Tue, 28 Apr 2020 17:14:10 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Kenny Levinsen <kl@...wtf>
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        daniel@...ll.ch, airlied@...ux.ie, tzimmermann@...e.de,
        mripard@...nel.org, maarten.lankhorst@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm: make drm_file use keyed wakeups

On Fri, Apr 24, 2020 at 06:26:15PM +0200, Kenny Levinsen wrote:
> 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@...wtf>

Hm I applied v1 and I'm not spotting what's different here, and there's no
changelog explaining what changed ...

Please send a fixup if there's anything important missing.
-Daniel

> ---
>  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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch