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From: Pekka Paalanen <ppaalanen@gmail.com>
To: Esaki Tomohito <etom@igel.co.jp>
Cc: Thomas Zimmermann <tzimmermann@suse.de>,
	devicetree@vger.kernel.org, Takanari Hayama <taki@igel.co.jp>,
	linux-doc@vger.kernel.org, David Airlie <airlied@linux.ie>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	linux-renesas-soc@vger.kernel.org,
	Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Damian Hobson-Garcia <dhobsong@igel.co.jp>
Subject: Re: [PATH 0/4] [RFC] Support virtual DRM
Date: Tue, 22 Jun 2021 10:57:57 +0300	[thread overview]
Message-ID: <20210622105757.2b9dec32@eldfell> (raw)
In-Reply-To: <85593f2f-5aa9-6023-ecba-c5275a468b71@igel.co.jp>

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On Tue, 22 Jun 2021 13:02:59 +0900
Esaki Tomohito <etom@igel.co.jp> wrote:

> Hi, Thomas
> Thank you for reply.
> 
> On 2021/06/21 16:10, Thomas Zimmermann wrote:
> > Hi
> > 
> > Am 21.06.21 um 08:27 schrieb Tomohito Esaki:  
> >> Virtual DRM splits the overlay planes of a display controller into
> >> multiple
> >> virtual devices to allow each plane to be accessed by each process.
> >>
> >> This makes it possible to overlay images output from multiple
> >> processes on a
> >> display. For example, one process displays the camera image without
> >> compositor
> >> while another process overlays the UI.  
> > 
> > I briefly looked over your patches. I didn't understand how this is
> > different to the functionality of a compositor? Shouldn't this be solved
> > in userspace?  
> 
> I think when latency is important (e.g., AR, VR, for displaying camera
> images in IVI systems), there may be use cases where the compositor
> cannot be used.

Hi,

> Normally, when the image is passed through the compositor, it is
> displayed after 2 VSYNC at most, because the compositor combines the
> image with VSYNC synchronization.

This is not a universal fact. You can write a Wayland compositor that
consistently reaches app-to-screen latency of less than one monitor
refresh cycle, while also using KMS planes.

I believe Weston succeeds in this already if you write the Wayland
application accordingly.


Thanks,
pq

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WARNING: multiple messages have this Message-ID (diff)
From: Pekka Paalanen <ppaalanen@gmail.com>
To: Esaki Tomohito <etom@igel.co.jp>
Cc: devicetree@vger.kernel.org, Takanari Hayama <taki@igel.co.jp>,
	linux-doc@vger.kernel.org, David Airlie <airlied@linux.ie>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-renesas-soc@vger.kernel.org,
	Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Damian Hobson-Garcia <dhobsong@igel.co.jp>
Subject: Re: [PATH 0/4] [RFC] Support virtual DRM
Date: Tue, 22 Jun 2021 10:57:57 +0300	[thread overview]
Message-ID: <20210622105757.2b9dec32@eldfell> (raw)
In-Reply-To: <85593f2f-5aa9-6023-ecba-c5275a468b71@igel.co.jp>

[-- Attachment #1: Type: text/plain, Size: 1463 bytes --]

On Tue, 22 Jun 2021 13:02:59 +0900
Esaki Tomohito <etom@igel.co.jp> wrote:

> Hi, Thomas
> Thank you for reply.
> 
> On 2021/06/21 16:10, Thomas Zimmermann wrote:
> > Hi
> > 
> > Am 21.06.21 um 08:27 schrieb Tomohito Esaki:  
> >> Virtual DRM splits the overlay planes of a display controller into
> >> multiple
> >> virtual devices to allow each plane to be accessed by each process.
> >>
> >> This makes it possible to overlay images output from multiple
> >> processes on a
> >> display. For example, one process displays the camera image without
> >> compositor
> >> while another process overlays the UI.  
> > 
> > I briefly looked over your patches. I didn't understand how this is
> > different to the functionality of a compositor? Shouldn't this be solved
> > in userspace?  
> 
> I think when latency is important (e.g., AR, VR, for displaying camera
> images in IVI systems), there may be use cases where the compositor
> cannot be used.

Hi,

> Normally, when the image is passed through the compositor, it is
> displayed after 2 VSYNC at most, because the compositor combines the
> image with VSYNC synchronization.

This is not a universal fact. You can write a Wayland compositor that
consistently reaches app-to-screen latency of less than one monitor
refresh cycle, while also using KMS planes.

I believe Weston succeeds in this already if you write the Wayland
application accordingly.


Thanks,
pq

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  reply	other threads:[~2021-06-22  7:58 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-21  6:27 [PATH 0/4] [RFC] Support virtual DRM Tomohito Esaki
2021-06-21  6:27 ` [PATH 1/4] drm: Add Virtual DRM device driver Tomohito Esaki
2021-06-21  6:27 ` [PATH 2/4] rcar-du: Add support virtual DRM device Tomohito Esaki
2021-06-21  6:27 ` [PATH 3/4] dt-bindings: display: Add virtual DRM Tomohito Esaki
2021-06-21  6:27 ` [PATH 4/4] doc-rst: Add virtual DRM documentation Tomohito Esaki
2021-06-21  7:10 ` [PATH 0/4] [RFC] Support virtual DRM Thomas Zimmermann
2021-06-21  9:24   ` Maxime Ripard
2021-06-22  4:36     ` Esaki Tomohito
2021-06-22  4:36       ` Esaki Tomohito
2021-06-23 14:39       ` Maxime Ripard
2021-06-23 14:39         ` Maxime Ripard
2021-06-22  4:02   ` Esaki Tomohito
2021-06-22  4:02     ` Esaki Tomohito
2021-06-22  7:57     ` Pekka Paalanen [this message]
2021-06-22  7:57       ` Pekka Paalanen
2021-06-23  8:04       ` Michel Dänzer
2021-06-23  8:21         ` Esaki Tomohito
2021-06-22  9:12     ` Thomas Zimmermann
2021-06-22  9:12       ` Thomas Zimmermann
2021-06-21 16:05 ` Enrico Weigelt, metux IT consult
2021-06-22  4:03   ` Esaki Tomohito
2021-06-22  4:03     ` Esaki Tomohito
2021-06-22  8:12     ` Pekka Paalanen
2021-06-22  8:12       ` Pekka Paalanen
2021-06-22 19:12       ` Daniel Vetter
2021-06-22 19:12         ` Daniel Vetter
2021-06-23  6:56       ` Esaki Tomohito
2021-06-23  6:56         ` Esaki Tomohito
2021-06-23  8:39         ` Pekka Paalanen
2021-06-23  8:39           ` Pekka Paalanen
2021-06-23  9:22           ` Esaki Tomohito
2021-06-23  9:22             ` Esaki Tomohito
2021-06-23 11:41             ` Pekka Paalanen
2021-06-23 11:41               ` Pekka Paalanen
2021-06-25  1:55               ` Esaki Tomohito
2021-06-25  1:55                 ` Esaki Tomohito
2021-06-21  6:43 Tomohito Esaki
2021-06-21  6:43 ` Tomohito Esaki
2021-06-22  8:04 ` Simon Ser
2021-06-22  8:04   ` Simon Ser

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