Lines Matching +full:required +full:- +full:for +full:- +full:hardware +full:- +full:jobs
1 Buffer Sharing and Synchronization (dma-buf)
4 The dma-buf subsystem provides the framework for sharing buffers for
5 hardware (DMA) access across multiple device drivers and subsystems, and
6 for synchronizing asynchronous hardware access.
14 interact with the three main primitives offered by dma-buf:
16 - dma-buf, representing a sg_table and exposed to userspace as a file
19 - dma-fence, providing a mechanism to signal when an asynchronous
20 hardware operation has completed; and
21 - dma-resv, which manages a set of dma-fences for a particular dma-buf
22 allowing implicit (kernel-ordered) synchronization of work to
27 --------------------------------
29 For more details on how to design your subsystem's API for dma-buf use, please
30 see Documentation/userspace-api/dma-buf-alloc-exchange.rst.
34 ------------------
36 This document serves as a guide to device-driver writers on what is the dma-buf
37 buffer sharing API, how to use it for exporting and using shared buffers.
43 exporter, and A as buffer-user/importer.
47 - implements and manages operations in :c:type:`struct dma_buf_ops
48 <dma_buf_ops>` for the buffer,
49 - allows other users to share the buffer by using dma_buf sharing APIs,
50 - manages the details of buffer allocation, wrapped in a :c:type:`struct
52 - decides about the actual backing storage where this allocation happens,
53 - and takes care of any migration of scatterlist - for all (shared) users of
56 The buffer-user
58 - is one of (many) sharing users of the buffer.
59 - doesn't need to worry about how the buffer is allocated, or where.
60 - and needs a mechanism to get access to the scatterlist that makes up this
65 Any exporters or users of the dma-buf buffer sharing framework must have a
71 Mostly a DMA buffer file descriptor is simply an opaque object for userspace,
75 - Since kernel 3.12 the dma-buf FD supports the llseek system call, but only
78 llseek operation will report -EINVAL.
80 If llseek on dma-buf FDs isn't supported the kernel will report -ESPIPE for all
81 cases. Userspace can use this to detect support for discovering the dma-buf
84 - In order to avoid fd leaks on exec, the FD_CLOEXEC flag must be set
92 multi-threaded app[3]. The issue is made worse when it is library code
97 flag be set when the dma-buf fd is created. So any API provided by
101 - Memory mapping the contents of the DMA buffer is also supported. See the
102 discussion below on `CPU Access to DMA Buffer Objects`_ for the full details.
104 - The DMA buffer FD is also pollable, see `Implicit Fence Poll Support`_ below for
107 - The DMA buffer FD also supports a few dma-buf-specific ioctls, see
108 `DMA Buffer ioctls`_ below for details.
113 .. kernel-doc:: drivers/dma-buf/dma-buf.c
119 .. kernel-doc:: drivers/dma-buf/dma-buf.c
125 .. kernel-doc:: drivers/dma-buf/dma-buf.c
128 DMA-BUF statistics
130 .. kernel-doc:: drivers/dma-buf/dma-buf-sysfs-stats.c
136 .. kernel-doc:: include/uapi/linux/dma-buf.h
138 DMA-BUF locking convention
141 .. kernel-doc:: drivers/dma-buf/dma-buf.c
147 .. kernel-doc:: drivers/dma-buf/dma-buf.c
150 .. kernel-doc:: include/linux/dma-buf.h
154 -------------------
156 .. kernel-doc:: drivers/dma-buf/dma-resv.c
159 .. kernel-doc:: drivers/dma-buf/dma-resv.c
162 .. kernel-doc:: include/linux/dma-resv.h
166 ----------
168 .. kernel-doc:: drivers/dma-buf/dma-fence.c
171 DMA Fence Cross-Driver Contract
174 .. kernel-doc:: drivers/dma-buf/dma-fence.c
175 :doc: fence cross-driver contract
180 .. kernel-doc:: drivers/dma-buf/dma-fence.c
186 .. kernel-doc:: drivers/dma-buf/dma-fence.c
192 .. kernel-doc:: drivers/dma-buf/dma-fence.c
195 .. kernel-doc:: include/linux/dma-fence.h
201 .. kernel-doc:: drivers/dma-buf/dma-fence-array.c
204 .. kernel-doc:: include/linux/dma-fence-array.h
210 .. kernel-doc:: drivers/dma-buf/dma-fence-chain.c
213 .. kernel-doc:: include/linux/dma-fence-chain.h
219 .. kernel-doc:: include/linux/dma-fence-unwrap.h
225 .. kernel-doc:: drivers/dma-buf/sync_file.c
228 .. kernel-doc:: include/linux/sync_file.h
234 .. kernel-doc:: include/uapi/linux/sync_file.h
247 * Proxy fences, proposed to handle &drm_syncobj for which the fence has not yet
250 * Userspace fences or gpu futexes, fine-grained locking within a command buffer
251 that userspace uses for synchronization across engines or with the CPU, which
252 are then imported as a DMA fence for integration into existing winsys
255 * Long-running compute command buffers, while still using traditional end of
256 batch DMA fences for memory management instead of context preemption DMA
261 in-kernel DMA fences does not work, even when a fallback timeout is included to
271 for memory management needs, which means we must support indefinite fences being
274 potential for deadlocks.
276 .. kernel-render:: DOT
284 kernel -> userspace [label="memory management"]
285 userspace -> kernel [label="Future fence, fence proxy, ..."]
303 * No DMA fences that signal end of batchbuffer for command submission where
305 workloads. This also means no implicit fencing for shared buffers in these
308 Recoverable Hardware Page Faults Implications
311 Modern hardware supports recoverable page faults, which has a lot of
312 implications for DMA fences.
315 accelerator and a memory allocation is usually required to resolve the fault.
317 means any workload using recoverable page faults cannot use DMA fences for
326 on-demand fill a memory request. For now this means recoverable page
334 - The 3D workload might need to wait for the compute job to finish and release
335 hardware resources first.
337 - The compute workload might be stuck in a page fault, because the memory
338 allocation is waiting for the DMA fence of the 3D workload to complete.
343 - Compute workloads can always be preempted, even when a page fault is pending
344 and not yet repaired. Not all hardware supports this.
346 - DMA fence workloads and workloads which need page fault handling have
347 independent hardware resources to guarantee forward progress. This could be
349 reservations for DMA fence workloads.
351 - The reservation approach could be further refined by only reserving the
352 hardware resources for DMA fence workloads when they are in-flight. This must
356 - As a last resort, if the hardware provides no useful reservation mechanics,
357 all workloads must be flushed from the GPU when switching between jobs
358 requiring DMA fences or jobs requiring page fault handling: This means all DMA
364 - Only a fairly theoretical option would be to untangle these dependencies when
365 allocating memory to repair hardware page faults, either through separate
369 robust to limit the impact of handling hardware page faults to the specific
372 Note that workloads that run on independent hardware like copy engines or other
374 in the kernel even for resolving hardware page faults, e.g. by using copy
381 hit a page fault which holds up a userspace fence - supporting page faults on