8 Aug
2019
8 Aug
'19
4:47 a.m.
Christan, any thoughts on v2?
--Jason
On August 7, 2019 09:06:47 Lionel Landwerlin lionel.g.landwerlin@intel.com wrote:
On 06/08/2019 19:19, Jason Ekstrand wrote:
This patch only brings the syncobj documentation up-to-date for the original form of syncobj. It does not contain any information about the design of timeline syncobjs.
v2: Incorporate feedback from Lionel and Christian:
- Mention actual ioctl and flag names
- Better language around reference counting
- Misc. language cleanups
Signed-off-by: Jason Ekstrand jason@jlekstrand.net
Reviewed-by: Lionel Landwerlin lionel.g.landwerlin@intel.com
drivers/gpu/drm/drm_syncobj.c | 98 +++++++++++++++++++++++++++++++---- 1 file changed, 87 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 1438dcb3ebb1..4b5c7b0ed714 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -29,21 +29,97 @@ /**
- DOC: Overview
- DRM synchronisation objects (syncobj, see struct &drm_syncobj) are
- persistent objects that contain an optional fence. The fence can be updated
- with a new fence, or be NULL.
- DRM synchronisation objects (syncobj, see struct &drm_syncobj) provide a
- container for a synchronization primitive which can be used by userspace
- to explicitly synchronize GPU commands, can be shared between userspace
- processes, and can be shared between different DRM drivers.
- Their primary use-case is to implement Vulkan fences and semaphores.
- The syncobj userspace API provides ioctls for several operations:
- syncobj's can be waited upon, where it will wait for the underlying
- fence.
- Creation and destruction of syncobjs
- Import and export of syncobjs to/from a syncobj file descriptor
- Import and export a syncobj's underlying fence to/from a sync file
- Reset a syncobj (set its fence to NULL)
- Signal a syncobj (set a trivially signaled fence)
- Wait for a syncobj's fence to appear and be signaled
- syncobj's can be export to fd's and back, these fd's are opaque and
- have no other use case, except passing the syncobj between processes.
- At it's core, a syncobj is simply a wrapper around a pointer to a struct
- &dma_fence which may be NULL.
- When a syncobj is first created, its pointer is either NULL or a pointer
- to an already signaled fence depending on whether the
- &DRM_SYNCOBJ_CREATE_SIGNALED flag is passed to
- &DRM_IOCTL_SYNCOBJ_CREATE.
- When GPU work which signals a syncobj is enqueued in a DRM driver,
- the syncobj fence is replaced with a fence which will be signaled by the
- completion of that work.
- When GPU work which waits on a syncobj is enqueued in a DRM driver, the
- driver retrieves syncobj's current fence at the time the work is enqueued
- waits on that fence before submitting the work to hardware.
- If the syncobj's fence is NULL, the enqueue operation is expected to fail.
- All manipulation of the syncobjs's fence happens in terms of the current
- fence at the time the ioctl is called by userspace regardless of whether
- that operation is an immediate host-side operation (signal or reset) or
- or an operation which is enqueued in some driver queue.
- &DRM_IOCTL_SYNCOBJ_RESET and &DRM_IOCTL_SYNCOBJ_SIGNAL can be used to
- manipulate a syncobj from the host by resetting its pointer to NULL or
- setting its pointer to a fence which is already signaled.
- Their primary use-case is to implement Vulkan fences and semaphores.
- syncobj have a kref reference count, but also have an optional file.
- The file is only created once the syncobj is exported.
- The file takes a reference on the kref.
- Host-side wait on syncobjs
- &DRM_IOCTL_SYNCOBJ_WAIT takes an array of syncobj handles and does a
- host-side wait on all of the syncobj fences simultaneously.
- If &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL is set, the wait ioctl will wait on
- all of the syncobj fences to be signaled before it returns.
- Otherwise, it returns once at least one syncobj fence has been signaled
- and the index of a signaled fence is written back to the client.
- Unlike the enqueued GPU work dependencies which fail if they see a NULL
- fence in a syncobj, if &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is set,
- the host-side wait will first wait for the syncobj to receive a non-NULL
- fence and then wait on that fence.
- If &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is not set and any one of the
- syncobjs in the array has a NULL fence, -EINVAL will be returned.
- Assuming the syncobj starts off with a NULL fence, this allows a client
- to do a host wait in one thread (or process) which waits on GPU work
- submitted in another thread (or process) without having to manually
- synchronize between the two.
- This requirement is inherited from the Vulkan fence API.
- Import/export of syncobjs
- &DRM_IOCTL_SYNCOBJ_FD_TO_HANDLE and &DRM_IOCTL_SYNCOBJ_HANDLE_TO_FD
- provide two mechanisms for import/export of syncobjs.
- The first lets the client import or export an entire syncobj to a file
- descriptor.
- These fd's are opaque and have no other use case, except passing the
- syncobj between processes.
- All exported file descriptors and any syncobj handles created as a
- result of importing those file descriptors own a reference to the
- same underlying struct &drm_syncobj and the syncobj can be used
- persistently across all the processes with which it is shared.
- The syncobj is freed only once the last reference is dropped.
- Unlike dma-buf, importing a syncobj creates a new handle (with its own
- reference) for every import instead of de-duplicating.
- The primary use-case of this persistent import/export is for shared
- Vulkan fences and semaphores.
- The second import/export mechanism, which is indicated by
- &DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE or
- &DRM_SYNCOBJ_HANDLE_TO_FD_FLAGS_EXPORT_SYNC_FILE lets the client
- import/export the syncobj's current fence from/to a &sync_file.
- When a syncobj is exported to a sync file, that sync file wraps the
- sycnobj's fence at the time of export and any later signal or reset
- operations on the syncobj will not affect the exported sync file.
- When a sync file is imported into a syncobj, the syncobj's fence is set
- to the fence wrapped by that sync file.
- Because sync files are immutable, resetting or signaling the syncobj
- will not affect any sync files whose fences have been imported into the
- syncobj.
*/
#include <linux/anon_inodes.h>