<div dir="ltr"><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Aug 22, 2019 at 9:55 AM Lionel Landwerlin <<a href="mailto:lionel.g.landwerlin@intel.com">lionel.g.landwerlin@intel.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">We've added a set of new APIs to manipulate syncobjs holding timelines of dma_fence. This adds a bit of documentation about how this works. Signed-off-by: Lionel Landwerlin <<a href="mailto:lionel.g.landwerlin@intel.com" target="_blank">lionel.g.landwerlin@intel.com</a>> Cc: Christian Koenig <<a href="mailto:Christian.Koenig@amd.com" target="_blank">Christian.Koenig@amd.com</a>> Cc: Jason Ekstrand <<a href="mailto:jason@jlekstrand.net" target="_blank">jason@jlekstrand.net</a>> Cc: David(ChunMing) Zhou <<a href="mailto:David1.Zhou@amd.com" target="_blank">David1.Zhou@amd.com</a>> --- drivers/gpu/drm/drm_syncobj.c | 87 +++++++++++++++++++++++++++++------ 1 file changed, 74 insertions(+), 13 deletions(-) diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index b5ad73330a48..32ffded6d2c0 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -43,27 +43,66 @@ * - Signal a syncobj (set a trivially signaled fence) * - Wait for a syncobj's fence to appear and be signaled * + * The syncobj userspace API also provides operations to manipulate a syncobj + * in terms of a timeline of struct &dma_fence rather than a single struct + * &dma_fence, through the following operations: + * + * - Signal a given point on the timeline + * - Wait for a given point to appear and/or be signaled + * - Import and export from/to a given point of a timeline + * * 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 + * + * If the syncobj is considered as a binary (signal/unsignaled) primitive, </blockquote><div> </div><div>What does "considered as a binary" mean? Is it an inherent property of the syncobj given at create time? Is it a state the syncobj can be in? Or is it a property of how the submit ioctl in the DRM driver references it? I'm really hoping it's either 1 or 3.... </div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> + * when GPU work is enqueued in a DRM driver to signal the syncobj, the fence + * is replaced with a fence which will be signaled by the completion of that + * work. + * If the syncobj is considered as a timeline primitive, when GPU work is + * enqueued in a DRM driver to signal the a given point of the syncobj, a new + * struct &dma_fence_chain pointing to the DRM driver's fence and also + * pointing to the previous fence that was in the syncobj. The new struct + * &dma_fence_chain fence put into the syncobj will be signaled by completion + * of the DRM driver's work and also any work associated with the fence + * previously in the syncobj. + * + * When GPU work which waits on a syncobj is enqueued in a DRM driver, at the + * time the work is enqueued, it waits on the fence coming from the syncobj + * before submitting the work to hardware. That fence is either : + * + * - The syncobj's current fence if the syncobj is considered as a binary + * primitive. + * - The struct &dma_fence associated with a given point if the syncobj is + * considered as a timeline primitive. + * + * If the syncobj's fence is NULL or not present in the syncobj's timeline, + * the enqueue operation is expected to fail. + * + * With binary syncobj, 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. * + * With timeline syncobj, all manipulation of the timeline fences happens in + * terms of the fence referred to in the timeline. See + * dma_fence_chain_find_seqno() to see how a given point is found in the + * timeline. + * + * Note that applications should be careful to always use timeline set of + * ioctl() when dealing with syncobj considered as timeline. Using a binary + * set of ioctl() with a syncobj considered as timeline could result incorrect + * synchronization. The use of binary syncobj is supported through the + * timeline set of ioctl() by using a point value of 0, this will reproduce + * the behavior of the binary set of ioctl() (for example replace the + * syncobj's fence when signaling). </blockquote><div> </div><div>I know I've asked this before but I feel compelled to ask it again. Why do we allow them to mix and match? Why not just have a create flag and enforce meaningful behavior? I'm a bit concerned that userspace is going to start relying on the subtlties of the interaction between timeline and binary syncobjs which are neither documented nor properly tested in IGT. </div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> + * * * Host-side wait on syncobjs * -------------------------- @@ -87,6 +126,16 @@ * synchronize between the two. * This requirement is inherited from the Vulkan fence API. * + * Similarly, &DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT takes an array of syncobj + * handles as well as an array of u64 points and does a host-side wait on all + * of syncobj fences at the given points simultaneously. + * + * &DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT also adds the ability to wait for a given + * fence to materialize on the timeline without waiting for the fence to be + * signaled by using the &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE flag. This + * requirement is inherited from the wait-before-signal behavior required by + * the Vulkan timeline semaphore API. + * * * Import/export of syncobjs * ------------------------- @@ -120,6 +169,18 @@ * Because sync files are immutable, resetting or signaling the syncobj * will not affect any sync files whose fences have been imported into the * syncobj. + * + * + * Import/export of timeline points in timeline syncobjs + * ----------------------------------------------------- + * + * &DRM_IOCTL_SYNCOBJ_TRANSFER provides a mechanism to transfer a struct + * &dma_fence of at a given point from a timeline syncobj to another point + * into another timeline syncobj. + * + * Note that if you want to transfer a struct &dma_fence from a given point on + * a timeline syncobj from/into a binary syncobj, you can use the point 0 to + * mean take/replace the fence in the syncobj. */ #include <linux/anon_inodes.h> -- 2.23.0 </blockquote></div></div>