| Message ID | 20200424092920.4801-1-sergey.senozhatsky@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Implement V4L2_BUF_FLAG_NO_CACHE_* flags | expand |
Hi Sergey, On 24/04/2020 11:29, Sergey Senozhatsky wrote: > Hello, > > v5 with fixes and improvements. > > I have a simple v4l-compliance patch now (will send it separately) which > tests cache and consistency hints. I ran compliance against the vivid > test driver, which was additionally extended with cache_hints module param: > Trimmed v4l-compliance output: > > - vivid with disabled cache hints support > > [..] > Buffer ioctls (Input 3): > test V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS: OK > test V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS: OK > test V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS: OK > test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: OK > test VIDIOC_EXPBUF: OK > [..] > > - vivid with enabled cache hints (cache_hints=1,...) > > [..] > Buffer ioctls (Input 3): > test V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS: OK > test V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS: OK > test V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS: OK > test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: OK > test VIDIOC_EXPBUF: OK > [..] > > > v4l-compliance revealed that we cannot reliably report > V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS, it's a bit special. > Let's look at fill_buf_caps() > > if (q->allow_cache_hints && q->io_modes & VB2_MMAP) > *caps |= V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS; > > There are several things here. First, if the queue is not setup yet > (we didn't call driver's ->queue_setup()) then ->allow_cache_hints > is expected to be 0. It's only in the ->queue_setup() that the driver > sets ->allow_cache_hints for those queues that can benefit from cache > management. What this means, is that if one does > > q.init(node->g_type(), memory); > q.reqbufs(node); > q.g_capabilities(); > > the cache hints cap will not be reported. We need to setup the queue > > q.init(node->g_type(), memory); > q.reqbufs(node, 1); > q.g_capabilities(); I missed that. What should happen is that q->allow_cache_hints is set by the driver before vb2_queue_init is called. And the documentation should be updated to say that the V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS flag is only valid when using the MMAP streaming I/O model. Perhaps the flag should be renamed to V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS to make this explicit? Other opinions are welcome. > > Second. Even if the queue is setup, we still can report wrong cache > hint values. Let's look at the following code > > fill_buf_caps(q, &p->capabilities); > if (!vb2_queue_allows_cache_hints(q)) > p->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT; The problem here is that vb2_queue_allows_cache_hints(q) uses stale information: the current streaming mode instead of the requested streaming mode. This should read: if (!q->allow_cache_hints || p->memory != V4L2_MEMORY_MMAP) p->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT; And V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS is always set regardless of the memory model. It just needs to be documented that this capability applies to MMAP mode only. > ret = vb2_core_reqbufs(...); > return ret; > > The thing here is that vb2_core_reqbufs() and vb2_core_create_bufs() > can re-initialize the queue and invoke ->queue_setup(), possibly > changing its memory model, etc. so cache hints cap which we set or > clear before vb2_core_reqbufs() and vb2_core_create_bufs() can become > invalid after we call those functions. It's the same with > ``req->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT``, we cannot clear > it before reqbufs()/create_bufs(). Therefore I added two simple > functions which fixup cache hint cap and non_consistent flag after > reqbufs()/create_bufs(). So the code looks like this now: > > fill_buf_caps(q, &p->capabilities); > ret = vb2_core_reqbufs(...); > fixup_consistency_attr(q, &p->flags); > fixup_cache_hints_cap(q, &p->capabilities); These fixup functions are ugly, unless I missed something I think the approach described above works just fine. With these changes I think it is ready to go in. Regards, Hans > return ret; > > > The rest is the pretty much the same. > > Previous series: > v4 link: https://lore.kernel.org/lkml/20200302041213.27662-1-senozhatsky@chromium.org/ > v3 link: https://lore.kernel.org/lkml/20200226111529.180197-1-senozhatsky@chromium.org > v2 link: https://lore.kernel.org/lkml/20200204025641.218376-1-senozhatsky@chromium.org/ > v1 link: https://lore.kernel.org/lkml/20191217032034.54897-1-senozhatsky@chromium.org/ > > Series Intro > ======================================================================== > > This is a reworked version of the vb2 cache hints > (V4L2_BUF_FLAG_NO_CACHE_INVALIDATE / V4L2_BUF_FLAG_NO_CACHE_CLEAN) > support patch series which previsouly was developed by Sakari and > Laurent [0]. > > The patch set attempts to preserve the existing behvaiour - cache > sync is performed in ->prepare() and ->finish() (unless the buffer > is DMA exported). User space can request “default behavior” override > with cache management hints, which are handled on a per-buffer basis > and should be supplied with v4l2_buffer ->flags during buffer > preparation. There are two possible hints: > > - V4L2_BUF_FLAG_NO_CACHE_INVALIDATE > No cache sync on ->finish() > > - V4L2_BUF_FLAG_NO_CACHE_CLEAN > No cache sync on ->prepare() > > In order to keep things on the safe side, we also require driver > to explicitly state which of its queues (if any) support user space > cache management hints (such queues should have ->allow_cache_hints > bit set). > > The patch set also (to some extent) simplifies allocators' ->prepare() > and ->finish() callbacks. Namely, we move cache management decision > making to the upper - core - layer. For example, if, previously, we > would have something like this > > vb2_buffer_done() > vb2_dc_finish() > if (buf->db_attach) > return; > > where each allocators' ->finish() callback would either bail > out (DMA exported buffer, for instance) or sync, now that "bail > out or sync" decision is made before we call into the allocator. > > Along with cache management hints, user space is also able to > adjust queue's memory consistency attributes. Memory consistency > attribute (dma_attrs) is per-queue, yet it plays its role on the > allocator level, when we allocate buffers’ private memory (planes). > For the time being, only one consistency attribute is supported: > DMA_ATTR_NON_CONSISTENT. > > [0] https://www.mail-archive.com/linux-media@vger.kernel.org/msg112459.html > > Sergey Senozhatsky (13): > videobuf2: use explicit unsigned int in vb2_queue > videobuf2: add cache management members > videobuf2: handle V4L2 buffer cache flags > videobuf2: add V4L2_FLAG_MEMORY_NON_CONSISTENT flag > videobuf2: add queue memory consistency parameter > videobuf2: handle V4L2_FLAG_MEMORY_NON_CONSISTENT flag > videobuf2: factor out planes prepare/finish functions > videobuf2: do not sync caches when we are allowed not to > videobuf2: check ->synced flag in prepare() and finish() > videobuf2: add begin/end cpu_access callbacks to dma-contig > videobuf2: add begin/end cpu_access callbacks to dma-sg > videobuf2: don't test db_attach in dma-contig prepare and finish > media: vivid: add cache_hints module param > > Documentation/admin-guide/media/vivid.rst | 9 ++ > .../userspace-api/media/v4l/buffer.rst | 41 +++++- > .../media/v4l/vidioc-create-bufs.rst | 7 +- > .../media/v4l/vidioc-reqbufs.rst | 20 ++- > .../media/common/videobuf2/videobuf2-core.c | 121 +++++++++++++----- > .../common/videobuf2/videobuf2-dma-contig.c | 41 +++++- > .../media/common/videobuf2/videobuf2-dma-sg.c | 38 ++++-- > .../media/common/videobuf2/videobuf2-v4l2.c | 93 +++++++++++++- > drivers/media/dvb-core/dvb_vb2.c | 2 +- > drivers/media/test-drivers/vivid/vivid-core.c | 9 ++ > drivers/media/test-drivers/vivid/vivid-core.h | 1 + > .../media/test-drivers/vivid/vivid-meta-cap.c | 5 + > .../media/test-drivers/vivid/vivid-meta-out.c | 5 + > .../media/test-drivers/vivid/vivid-sdr-cap.c | 7 + > .../test-drivers/vivid/vivid-touch-cap.c | 5 + > .../media/test-drivers/vivid/vivid-vbi-cap.c | 5 + > .../media/test-drivers/vivid/vivid-vbi-out.c | 5 + > .../media/test-drivers/vivid/vivid-vid-cap.c | 5 + > .../media/test-drivers/vivid/vivid-vid-out.c | 5 + > drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 9 +- > drivers/media/v4l2-core/v4l2-ioctl.c | 5 +- > include/media/videobuf2-core.h | 47 +++++-- > include/uapi/linux/videodev2.h | 13 +- > 23 files changed, 426 insertions(+), 72 deletions(-) >
On (20/04/28 16:47), Hans Verkuil wrote: > Hi Sergey, > > On 24/04/2020 11:29, Sergey Senozhatsky wrote: [..] > I missed that. What should happen is that q->allow_cache_hints is set by the > driver before vb2_queue_init is called. And the documentation should be updated > to say that the V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS flag is only valid when using the > MMAP streaming I/O model. > > Perhaps the flag should be renamed to V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS to > make this explicit? Other opinions are welcome. > > > > > Second. Even if the queue is setup, we still can report wrong cache > > hint values. Let's look at the following code > > > > fill_buf_caps(q, &p->capabilities); > > if (!vb2_queue_allows_cache_hints(q)) > > p->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT; > > The problem here is that vb2_queue_allows_cache_hints(q) uses stale information: > the current streaming mode instead of the requested streaming mode. > > This should read: > > if (!q->allow_cache_hints || p->memory != V4L2_MEMORY_MMAP) > p->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT; > > And V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS is always set regardless of the > memory model. It just needs to be documented that this capability applies > to MMAP mode only. > > > ret = vb2_core_reqbufs(...); > > return ret; > > > > The thing here is that vb2_core_reqbufs() and vb2_core_create_bufs() > > can re-initialize the queue and invoke ->queue_setup(), possibly > > changing its memory model, etc. so cache hints cap which we set or > > clear before vb2_core_reqbufs() and vb2_core_create_bufs() can become > > invalid after we call those functions. It's the same with > > ``req->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT``, we cannot clear > > it before reqbufs()/create_bufs(). Therefore I added two simple > > functions which fixup cache hint cap and non_consistent flag after > > reqbufs()/create_bufs(). So the code looks like this now: > > > > fill_buf_caps(q, &p->capabilities); > > ret = vb2_core_reqbufs(...); > > fixup_consistency_attr(q, &p->flags); > > fixup_cache_hints_cap(q, &p->capabilities); > > These fixup functions are ugly, unless I missed something I think the > approach described above works just fine. > > With these changes I think it is ready to go in. ACK to all of these. Will send the updated patch set shortly. -ss