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gst: pool: Keep dmabufs mapped

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Downstream elements accessing dmabufs from the CPU currently need to map
and unmap buffers on every frame.
While the kernel's page cache avoids most overhead, this still requires a
round-trip through the kernel and possibly non-negligible work in
`dma_buf_mmap()`. Keeping the buffers mapped avoids that without causing
additional syncronization work, as the later should only happen when
`DMA_BUF_IOCTL_SYNC` is triggered in `gst_dmabuf_mem_map()`.

A common scenario where this matters is clients using cameras. The
downstream elements in question may not be aware of dmabufs - e.g.
`videoconvert` - or fail to import the dmabuf and fall back to import
from memory - e.g. `glupload`.

Notes:
 - GstShmAllocator implicitly does this already.
 - We could also do this in the MemFd case, however I'm less convinced
   about the trade-offs.
This commit is contained in:
Robert Mader 2025-08-23 14:58:18 +02:00
parent 95497f8777
commit 5f3ae4376e
1 changed files with 20 additions and 1 deletions
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21
src/gst/gstpipewirepool.c
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@ -158,9 +158,28 @@ void gst_pipewire_pool_wrap_buffer (GstPipeWirePool *pool, struct pw_buffer *b)
gst_memory_resize (gmem, d->mapoffset, d->maxsize);
}
else if(d->type == SPA_DATA_DmaBuf) {
GstMapInfo info = { 0 };
GstFdMemoryFlags fd_flags = GST_FD_MEMORY_FLAG_NONE;
if (d->flags & SPA_DATA_FLAG_MAPPABLE && d->flags & SPA_DATA_FLAG_READABLE)
fd_flags |= GST_FD_MEMORY_FLAG_KEEP_MAPPED;
gmem = gst_fd_allocator_alloc (pool->dmabuf_allocator, dup(d->fd),
d->mapoffset + d->maxsize, GST_FD_MEMORY_FLAG_NONE);
d->mapoffset + d->maxsize, fd_flags);
gst_memory_resize (gmem, d->mapoffset, d->maxsize);
if (fd_flags & GST_FD_MEMORY_FLAG_KEEP_MAPPED) {
GstMapFlags map_flags = GST_MAP_READ;
if (d->flags & SPA_DATA_FLAG_WRITABLE)
map_flags |= GST_MAP_WRITE;
if (gst_memory_map (gmem, &info, map_flags)) {
gst_memory_unmap (gmem, &info);
} else {
GST_ERROR_OBJECT (pool, "mmaping buffer failed");
}
}
}
else if (d->type == SPA_DATA_MemPtr) {
gmem = gst_memory_new_wrapped (0, d->data, d->maxsize, 0,