[PATCH wayland-protocols v4] Add zwp_linux_explicit_synchronization_v1
Pekka Paalanen
ppaalanen at gmail.com
Wed Oct 31 11:22:41 UTC 2018
On Thu, 18 Oct 2018 16:48:53 +0300
Alexandros Frantzis <alexandros.frantzis at collabora.com> wrote:
> Signed-off-by: Alexandros Frantzis <alexandros.frantzis at collabora.com>
> ---
>
> Changes in patch v4:
> - Guarantee protocol compatibility only with zwp_linux_dmabuf buffers.
> - Add the UNSUPPORTED_BUFFER error.
>
> Changes in patch v3:
> - Reworded implicit/explicit synchronization intro in
> zwp_surface_synchronization_v1 description.
> - Removed confusing mention of wl_buffer.release in
> zwp_surface_synchronization_v1 description.
> - Clarified which fences are affected on sync object destruction.
> - Removed unclear mention about wl_buffer destruction
> in fenced_release description.
> - Clarified that the release events and their guarantees apply to
> the relevant commit only.
> - Reformatted text.
>
> Changes in patch v2:
> - Added NO_SURFACE error for zwp_surface_synchronization_v1 requests.
> - Removed restriction to destroy a zwp_surface_synchronization_v1 object
> after the associated wl_surface is destroyed.
> - Clarified which buffer the acquire fence is associated with.
> - Clarified that exactly one event, either a fenced_release or a
> immediate_release, will be emitted for each commit.
>
> patch v1 here: https://patchwork.freedesktop.org/patch/177866/
Hi Alf,
looks even better! Just few details below I'd still like to clarify.
>
> Makefile.am | 1 +
> .../linux-explicit-synchronization/README | 6 +
> ...x-explicit-synchronization-unstable-v1.xml | 232 ++++++++++++++++++
> 3 files changed, 239 insertions(+)
> create mode 100644 unstable/linux-explicit-synchronization/README
> create mode 100644 unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml
>
> diff --git a/Makefile.am b/Makefile.am
> index 6394e26..7dfbb9e 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -21,6 +21,7 @@ unstable_protocols = \
> unstable/xdg-output/xdg-output-unstable-v1.xml \
> unstable/input-timestamps/input-timestamps-unstable-v1.xml \
> unstable/xdg-decoration/xdg-decoration-unstable-v1.xml \
> + unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml \
> $(NULL)
>
> stable_protocols = \
> diff --git a/unstable/linux-explicit-synchronization/README b/unstable/linux-explicit-synchronization/README
> new file mode 100644
> index 0000000..f13b404
> --- /dev/null
> +++ b/unstable/linux-explicit-synchronization/README
> @@ -0,0 +1,6 @@
> +Linux explicit synchronization (dma-fence) protocol
> +
> +Maintainers:
> +David Reveman <reveman at chromium.org>
> +Daniel Stone <daniels at collabora.com>
> +Alexandros Frantzis <alexandros.frantzis at collabora.com>
> diff --git a/unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml b/unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml
> new file mode 100644
> index 0000000..4800756
> --- /dev/null
> +++ b/unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml
> @@ -0,0 +1,232 @@
> +<?xml version="1.0" encoding="UTF-8"?>
> +<protocol name="zwp_linux_explicit_synchronization_unstable_v1">
> +
> + <copyright>
> + Copyright 2016 The Chromium Authors.
> + Copyright 2017 Intel Corporation
> + Copyright 2018 Collabora, Ltd
> +
> + Permission is hereby granted, free of charge, to any person obtaining a
> + copy of this software and associated documentation files (the "Software"),
> + to deal in the Software without restriction, including without limitation
> + the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + and/or sell copies of the Software, and to permit persons to whom the
> + Software is furnished to do so, subject to the following conditions:
> +
> + The above copyright notice and this permission notice (including the next
> + paragraph) shall be included in all copies or substantial portions of the
> + Software.
> +
> + THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> + THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> + DEALINGS IN THE SOFTWARE.
> + </copyright>
> +
> + <interface name="zwp_linux_explicit_synchronization_v1" version="1">
> + <description summary="protocol for providing explicit synchronization">
> + This global is a factory interface, allowing clients to request
> + explicit synchronization for buffers on a per-surface basis.
> +
> + See zwp_surface_synchronization_v1 for more information.
> +
> + This interface is derived from Chromium's
> + zcr_linux_explicit_synchronization_v1.
> +
> + Warning! The protocol described in this file is experimental and
> + backward incompatible changes may be made. Backward compatible changes
> + may be added together with the corresponding interface version bump.
> + Backward incompatible changes are done by bumping the version number in
> + the protocol and interface names and resetting the interface version.
> + Once the protocol is to be declared stable, the 'z' prefix and the
> + version number in the protocol and interface names are removed and the
> + interface version number is reset.
> + </description>
> +
> + <request name="destroy" type="destructor">
> + <description summary="destroy explicit synchronization factory object">
> + Destroy this explicit synchronization factory object. Other objects,
> + including zwp_surface_synchronization_v1 objects created by this
> + factory, shall not be affected by this request.
> + </description>
> + </request>
> +
> + <enum name="error">
> + <entry name="synchronization_exists" value="0"
> + summary="the surface already has a synchronization object associated"/>
> + </enum>
> +
> + <request name="get_synchronization">
> + <description summary="extend surface interface for explicit synchronization">
> + Instantiate an interface extension for the given wl_surface to provide
> + explicit synchronization.
> +
> + If the given wl_surface already has an explicit synchronization object
> + associated, the synchronization_exists protocol error is raised.
> + </description>
> +
> + <arg name="id" type="new_id" interface="zwp_surface_synchronization_v1"
> + summary="the new synchronization interface id"/>
> + <arg name="surface" type="object" interface="wl_surface"
> + summary="the surface"/>
> + </request>
> + </interface>
> +
> + <interface name="zwp_surface_synchronization_v1" version="1">
> + <description summary="per-surface explicit synchronization support">
> + This object implements per-surface explicit synchronization.
> +
> + Synchronization refers to co-ordination of pipelined operations performed
> + on buffers. Most GPU clients will schedule an asynchronous operation to
> + render to the buffer, then immediately send the buffer to the compositor
> + to be attached to a surface.
> +
> + In implicit synchronization, ensuring that the rendering operation is
> + complete before the compositor displays the buffer is an implementation
> + detail handled by either the kernel or userspace graphics driver.
> +
> + By contrast, in explicit synchronization, dma_fence objects mark when the
> + asynchronous operations are complete. When submitting a buffer, the
> + client provides an acquire fence which will be waited on before the
> + compositor accesses the buffer. The Wayland server, through a
> + zwp_buffer_release_v1 object, will inform the client with an event which
> + may be accompanied by a release fence, when the buffer can be
> + destructively accessed.
Since this is actually handled per-commit, unlike the old
wl_buffer.release event which is defined as "can be destructively
accessed", the wording here could be more like:
"when the compositor will no longer access the buffer contents due to
the specific commit that requested the release event."
It's hard to word clearly and conscisely, but I hope you get the idea
of how this different from "can be destructively accessed" which is a
global concept rather than tied to a specific commit. A client may do
several commits on same or different wl_surfaces, and only after they
all have signalled the explicit fence release, the destructive access is
harmless.
The reason why https://gitlab.freedesktop.org/wayland/wayland/issues/46
is essentially unsolvable without new protocol is that
wl_buffer.release is not tied to a specific commit. If a client commits
the same buffer several times (same or different wl_surfaces), it
cannot know how many wl_buffer.release events it needs before the
buffer really is free due to asynchronicity of the protocol.
Therefore to me the point that the new release event is scoped only to
the specific commit is very important.
> +
> + Each surface can be associated with only one object of this interface at
> + any time.
> +
> + Explicit synchronization is guaranteed to be supported only for buffers
> + created with any version of the zwp_linux_dmabuf buffer factory.
Maybe this limitation should be for set_acquire_fence only? See below
about get_release.
> + </description>
> +
> + <request name="destroy" type="destructor">
> + <description summary="destroy synchronization object">
> + Destroy this explicit synchronization object.
> +
> + Any fence set by this object with set_acquire_fence since the last
> + commit will be discarded by the server. Any fences set by this object
> + before the last commit are not affected.
> +
> + zwp_buffer_release_v1 objects created by this object are not affected
> + by this request.
> + </description>
> + </request>
> +
> + <enum name="error">
> + <entry name="invalid_fence" value="0"
> + summary="the fence specified by the client could not be imported"/>
> + <entry name="duplicate_fence" value="1"
> + summary="multiple fences added for a single surface commit"/>
> + <entry name="duplicate_release" value="2"
> + summary="multiple releases added for a single surface commit"/>
> + <entry name="no_surface" value="3"
> + summary="the associated wl_surface was destroyed"/>
> + <entry name="unsupported_buffer" value="4"
> + summary="the buffer does not support explicit synchronization"/>
> + </enum>
> +
> + <request name="set_acquire_fence">
> + <description summary="set the acquire fence">
> + Set the acquire fence that must be signaled before the compositor
> + may sample from the buffer attached with wl_buffer_attach. The fence
> + is a dma_fence kernel object.
> +
> + The acquire fence is double-buffered state, and will be applied on the
> + next wl_surface.commit request for the associated surface. Thus, it
> + applies only to the buffer that is attached to the surface at commit
> + time.
> +
> + If the fence could not be imported, an INVALID_FENCE error is raised.
Should we allow raising INVALID_FENCE on wl_surface.commit, or are we
sure the import happens in full at set_acquire_fence time?
> +
> + If a fence has already been attached during the same commit cycle, a
> + DUPLICATE_FENCE error is raised.
> +
> + If the associated wl_surface was destroyed, a NO_SURFACE error is
> + raised.
> +
> + If at surface commit time the attached buffer does not support explicit
> + synchronization, or there is no buffer attached, an UNSUPPORTED_BUFFER
> + error is raised.
> + </description>
> + <arg name="fd" type="fd" summary="acquire fence fd"/>
> + </request>
> +
> + <request name="get_release">
> + <description summary="release fence for last-attached buffer">
> + Create a listener for the release of the buffer attached by the
> + client with wl_buffer.attach. See zwp_buffer_release_v1
> + documentation for more information.
> +
> + The release object is double-buffered state, and will be applied
> + on the next wl_surface.commit request for the associated surface.
> +
> + If a zwp_buffer_release_v1 object has already been requested for
> + the surface in the same commit cycle, a DUPLICATE_RELEASE error
> + is signaled to the client.
> +
> + If the associated wl_surface was destroyed, a NO_SURFACE error
> + is signaled to the client.
> +
> + If at surface commit time the attached buffer does not support
> + explicit synchronization, or there is no buffer attached, an
> + UNSUPPORTED_BUFFER error is raised.
Is UNSUPPORTED_BUFFER error actually necessary here? Why would the
buffer type affect whether the compositor can service a
zwp_buffer_release object or not?
In the worst case, the compositor will not be able to provide release
fence fd, in which case it can always rely on immediate_release event.
If we allow get_release for all buffer types, immediate_release becomes
like wl_buffer.release but scoped to the specific commit, fixing
https://gitlab.freedesktop.org/wayland/wayland/issues/46 for everything.
It will be up to the client to decide to use get_release on whether it
can handle both immediate_release and fenced_release.
> + </description>
> +
> + <arg name="release" type="new_id" interface="zwp_buffer_release_v1"
> + summary="new zwp_buffer_release_v1 object"/>
> + </request>
> + </interface>
> +
> + <interface name="zwp_buffer_release_v1" version="1">
> + <description summary="buffer release explicit synchronization">
> + This object is instantiated in response to a
> + zwp_surface_synchronization_v1.get_release request.
> +
> + It provides an alternative to wl_buffer.release events, providing a unique
> + release from a single wl_surface.commit request. The release event also
> + supports explicit synchronization, providing a fence FD where relevant for
> + the client to synchronize against before reusing the buffer.
> +
> + Exactly one event, either a fenced_release or an immediate_release, will
> + be emitted for each wl_surface.commit request.
Should we add something like: "The compositor can choose release by
release which event it uses."
Just to underline that clients really need to be prepared to deal with
both kinds if they use get_release?
Or is already clear enough?
> +
> + This event does not replace wl_buffer.release events; servers are still
> + required to send those events.
> + </description>
> +
> + <request name="destroy" type="destructor">
> + <description summary="destroy buffer release synchronization object">
> + Destroy this buffer release explicit synchronization object. The object
> + may be destroyed at any time.
> + </description>
> + </request>
We can keep the destroy request for now, removing it would be just a
minor optimization.
> +
> + <event name="fenced_release">
> + <description summary="release buffer with fence">
> + Sent when the compositor has finalised its usage of the associated
> + buffer for the relevant commit, providing a dma_fence which will be
> + signaled when all operations by the compositor on that buffer for that
> + commit have finished.
> +
> + Clients must not perform any destructive operations (e.g. clearing or
> + rendering) on the buffer until that fence has signaled.
> + </description>
> + <arg name="fence" type="fd" summary="fence for last operation on buffer"/>
> + </event>
> +
> + <event name="immediate_release">
> + <description summary="release buffer immediately">
> + Sent when the compositor has finalised its usage of the associated
> + buffer for the relevant commit, and either performed no operations
> + using it, or has a guarantee that all its operations on that buffer for
> + that commit have finished, and any destructive operations on the buffer
> + will have no external effects.
> + </description>
> + </event>
> + </interface>
> +
> +</protocol>
Thanks,
pq
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 833 bytes
Desc: OpenPGP digital signature
URL: <https://lists.freedesktop.org/archives/wayland-devel/attachments/20181031/1ac302fd/attachment-0001.sig>
More information about the wayland-devel
mailing list