[Libva] [PATCH v3 intel-driver 3/9] decoder: h264: simplify and optimize reference frame store updates.
Gwenole Beauchesne
gb.devel at gmail.com
Thu Jun 5 09:20:43 PDT 2014
2014-06-05 17:29 GMT+02:00 Xiang, Haihao <haihao.xiang at intel.com>:
>
>
>> -----Original Message-----
>> From: Gwenole Beauchesne [mailto:gb.devel at gmail.com]
>> Sent: Thursday, June 05, 2014 9:29 PM
>> To: Xiang, Haihao
>> Cc: Zhao, Yakui; libva at lists.freedesktop.org
>> Subject: Re: [Libva] [PATCH v3 intel-driver 3/9] decoder: h264: simplify and
>> optimize reference frame store updates.
>>
>> Hi,
>>
>> 2014-06-05 14:44 GMT+02:00 Xiang, Haihao <haihao.xiang at intel.com>:
>> >
>> >
>> >> -----Original Message-----
>> >> From: Libva [mailto:libva-bounces at lists.freedesktop.org] On Behalf Of
>> >> Gwenole Beauchesne
>> >> Sent: Thursday, June 05, 2014 5:20 PM
>> >> To: Zhao, Yakui
>> >> Cc: libva at lists.freedesktop.org
>> >> Subject: Re: [Libva] [PATCH v3 intel-driver 3/9] decoder: h264:
>> >> simplify and optimize reference frame store updates.
>> >>
>> >> 2014-06-04 7:30 GMT+02:00 Zhao, Yakui <yakui.zhao at intel.com>:
>> >> > On Tue, 2014-06-03 at 22:59 -0600, Gwenole Beauchesne wrote:
>> >> >> 2014-06-04 4:11 GMT+02:00 Zhao, Yakui <yakui.zhao at intel.com>:
>> >> >> > On Tue, 2014-06-03 at 10:43 -0600, Gwenole Beauchesne wrote:
>> >> >> >> Simplify and optimize the update process of the reference frame
>> store.
>> >> >> >> Use less iterations to look up existing objects. Use a cache to
>> >> >> >> store the free'd slots.
>> >> >> >>
>> >> >> >> Prerequisite: the reference_objects[] array was previously
>> >> >> >> arranged in a way that the element at index i is exactly the
>> >> >> >> object_surface that corresponds to the VA surface identified by
>> >> >> >> the VAPictureH264.picture_id located at index i in the
>> >> >> >> ReferenceFrames[]
>> >> array.
>> >> >> >
>> >> >> > As a whole, this patch looks good to me. Based on the hardware
>> >> >> > requirement, it will be better that one reference picture later
>> >> >> > used is not assigned for the other purpose even when it is not
>> >> >> > used in current reference frame list. In such case this patch
>> >> >> > does some optimization about DPB, which can defer the usage of
>> >> >> > one picture later used that is not in current reference frame.especially
>> when:
>> >> >> > one picture is not used during decoding frame X while it is used
>> >> >> > during
>> >> decoding frame X + 1.
>> >> >>
>> >> >> The case you mention was supposed to be fixed with the other patch
>> >> >> series where the re-factorisation is a pre-requisite. :) A very
>> >> >> strict GenFrameStoreContext needs to be maintained with the set of
>> >> >> used_frames[] as it is today, and an additional set of
>> >> >> free_frames[] *candidates*. Though, this case is not covered by
>> >> >> the conformance suite, and I haven't found any real world case
>> >> >> exhibiting that, neither did I try to generate one yet. So we can defer this
>> one.
>> >> >>
>> >> >> > Although it still has no improvment for the following scenario,
>> >> >> > it still is an improvement.
>> >> >> > >One picture is not used during decoding frame X and X + 1
>> >> >> > while it is used during decoding frame X + 2.
>> >> >> >
>> >> >> > Of course the perfect solution is that the upper layer can
>> >> >> > assure that one picture later used is still added into the DPB
>> >> >> > of current frame although it is not used in current reference list.
>> >> >>
>> >> >> No, this is not going to happen. This would be an implementation
>> >> >> error of the standard.
>> >> >
>> >> > In theory it is no problem for normal H264. But it is true for MVC
>> >> > case as some reference frames for view 1 is not used when decoding view
>> 0.
>> >>
>> >> When I said this was not going to happen, this concerned the "perfect
>> >> solution" you proposed, which is not one. That would be a workaround
>> >> to driver bugs, and an error of implementation of the standard. Of
>> >> course, the DPB holds all the necessary view components, but the
>> >> VAPictureH264.ReferenceFrames[] is not exactly the DPB, and it cannot be.
>> >
>> > The number of elements in VAPictureH264.ReferenceFrames[] is 16, so it
>> > is enough to hold All reference surfaces for H.264. and the patch works as
>> before, I am OK for your patch.
>> >
>> >>
>> >> The case you mention is what I said a paragraph above, and the only
>> "perfect"
>> >> way to solve it is to correctly track the references in the driver
>> >> side. This was what the GenFrameStoreContext was for. However, as I
>> >> mentioned, there is no supporting case in the conformance test suite,
>> >> and I haven't come by a real-world sample exhibiting this.
>> >
>> > The case Yakui mentioned is not for H.264 as a surface should be in
>> > DPB if it is referenced by later Surface.
>> >
>> > Xiaowei told us each view uses a separated DPB buffer for MVC
>>
>> There is no such thing in MVC. There is a unique DPB with a size scalable by a
>> log2 number of views.
>>
>> > A case might occurs as below:
>> >
>> > View0: f0, f1, f2, f3, ...
>> > View1: s0, s1, s2, s3, ...
>> >
>> > f0 is referenced by f1, but f0 isn't referenced by other surfaces in view0, f1
>> is reference by f2.
>> > F0 is also referenced by s1 , both f0 and f1 are referenced by S2 in
>> > view1
>> >
>> > When decoding f1, f0 is added into View0's DPB, so it is added into
>> > frame store too, the frame store index for f0 is *0*.
>> >
>> > When decoding s1, f0 is added into view1's DPB, it has been in the frame
>> store, the frame store index for f0 is still *0*.
>> >
>> > When decoding f2, f0 is removed from view0's DPB and f1 is added into
>> > view0's DPB, so f0 is removed from frame store and f1 is added into
>> > frame store too, now the frame store index For f1 is 0,
>> >
>> > When decoding s2, f0 is still in View1's DPB so it will be added into
>> > the frame store again, and now the frame store index for f0 is *1*
>> >
>> > The frame store index for f0 is changed from 0 to 1 and the decoding result
>> will be wrong.
>>
>> That's exactly the thing we are discussing since the beginning. :)
>
> The above case doesn't exist if MVC uses a unique DBP buffer as f0 is still in the DBP after
> Decoding f2, hence the driver won't remove f0 from the frame store.
Not necessarily. Anyway, your described case does not exist at all
because you can only have inter-view prediction with frames from the
same access unit. So, you cannot have f0+f1 referenced by s2, only f2
and s0+s1 could be referenced by s2. But anyway, that's the idea. A
valid example could be f1+f2 for s2, then f1+f2 for f3, then f3+s1+s2
for s3.
Because of the additional constraint I gave that ReferenceFrames[]
cannot always be the DPB because MVC is not limited to 2 views to
begin with, the case I describe is what will give issues. This is
because you cannot simply always append inter-view reference
components in the ReferenceFrames[] array because this is not scalable
for MultiView High with a higher number of views. This could work for
Stereo High because the DPB is always capped to 16 frames at most.
Besides, you'd better see the ReferenceFrames[] array as RefPicList0[]
U RefPicList1[] rather than the DPB. The DPB, as per the H.264 spec
definition, could have more than 16 entries for Multiview High
profile. And I don't really want to workaround/do different things for
Stereo High profile vs. Multiview High profile. So, the
ReferenceFrames[] is to be filled in with the reference frames
effectively used (L0+L1) for decoding the current picture.
Regards,
Gwenole.
>
>>
>> And there is no way to handle that from the unique GenFrameStore array as it
>> is today, even if you delay the marking as "free", or whatever.
>> You need a more elaborated data struct. And this is what was to be provided
>> with the GenFrameStoreContext and additional re-factoring so that I don't
>> have to copy code around again.
>>
>> I am working on an alternative that wouldn't need too many changes at this
>> time.
>>
>> Regards,
>> Gwenole.
>>
>> >
>> >>
>> >> >> >> Theory of operations:
>> >> >> >>
>> >> >> >> 1. Obsolete entries are removed first, i.e. entries in the internal DPB
>> >> >> >> that no longer have a match in the supplied ReferenceFrames[]
>> array.
>> >> >> >> That obsolete entry index is stored in a local cache: free_slots[].
>> >> >> >>
>> >> >> >> 2. This cache is completed with entries considered as "invalid" or "not
>> >> >> >> present", sequentially while traversing the frame store for
>> obsolete
>> >> >> >> entries. At the end of this removal process, the free_slots[] array
>> >> >> >> represents all possible indices in there that could be re-used for
>> >> >> >> new reference frames to track.
>> >> >> >>
>> >> >> >> 3. The list of ReferenceFrames[] objects is traversed for new entries
>> >> >> >> that are not already in the frame store. If an entry needs to be
>> >> >> >> added, it is placed at the index obtained from the next free_slots[]
>> >> >> >> element. There is no need to traverse the frame store array again,
>> >> >> >> the next available slot can be known from that free_slots[] cache.
>> >> >> >>
>> >> >> >> Signed-off-by: Gwenole Beauchesne
>> >> >> >> <gwenole.beauchesne at intel.com>
>> >> >> >> ---
>> >> >> >> src/i965_decoder_utils.c | 107
>> >> >> >> ++++++++++++++++++++--------------------------
>> >> >> >> 1 file changed, 46 insertions(+), 61 deletions(-)
>> >> >> >>
>> >> >> >> diff --git a/src/i965_decoder_utils.c
>> >> >> >> b/src/i965_decoder_utils.c index 2570be9..c686235 100644
>> >> >> >> --- a/src/i965_decoder_utils.c
>> >> >> >> +++ b/src/i965_decoder_utils.c
>> >> >> >> @@ -418,88 +418,73 @@ gen6_send_avc_ref_idx_state( }
>> >> >> >>
>> >> >> >> void
>> >> >> >> -intel_update_avc_frame_store_index(VADriverContextP ctx,
>> >> >> >> - struct decode_state
>> >> *decode_state,
>> >> >> >> -
>> >> VAPictureParameterBufferH264 *pic_param,
>> >> >> >> - GenFrameStore
>> >> frame_store[MAX_GEN_REFERENCE_FRAMES])
>> >> >> >> +intel_update_avc_frame_store_index(
>> >> >> >> + VADriverContextP ctx,
>> >> >> >> + struct decode_state *decode_state,
>> >> >> >> + VAPictureParameterBufferH264 *pic_param,
>> >> >> >> + GenFrameStore
>> >> frame_store[MAX_GEN_REFERENCE_FRAMES]
>> >> >> >> +)
>> >> >> >> {
>> >> >> >> - int i, j;
>> >> >> >> -
>> >> >> >> - assert(MAX_GEN_REFERENCE_FRAMES ==
>> >> ARRAY_ELEMS(pic_param->ReferenceFrames));
>> >> >> >> -
>> >> >> >> - for (i = 0; i < MAX_GEN_REFERENCE_FRAMES; i++) {
>> >> >> >> - int found = 0;
>> >> >> >> -
>> >> >> >> - if (frame_store[i].surface_id == VA_INVALID_ID ||
>> >> >> >> - frame_store[i].obj_surface == NULL)
>> >> >> >> + int free_slots[MAX_GEN_REFERENCE_FRAMES];
>> >> >> >> + int i, j, n, num_free_slots;
>> >> >> >> + bool found;
>> >> >> >> +
>> >> >> >
>> >> >> > It will be better to fill the free_slots through the following
>> >> >> > two loops instead of one loop, which is to try to defer the
>> >> >> > usage of the reference picture later used that is not used in
>> >> >> > current reference frame
>> >> list.
>> >> >> > a. check the invalid surface_id or NULL surface and then add it
>> >> >> > into free_slots.
>> >> >> > b. check whether one picture is used by the current reference
>> >> >> > frame list. If not, add it into the free_slots.
>> >> >>
>> >> >> The previous algorithm was filling in the holes. This one does the
>> >> >> same. I don't see where your proposal could bring an improvement?
>> >> >
>> >> > In your patch you use the free_slots to find one free slot to hold
>> >> > a new reference picture in DPB. Right? It will firstly try to find
>> >> > one free_slot with invalid picture_id or surface, which is used to
>> >> > hold a new reference picture in DPB.
>> >>
>> >> No, it will take whatever comes first between:
>> >> - a slot with an invalid picture_id or surface ;
>> >> - or a slot with a retired reference picture candidate, i.e.
>> >> something that cannot be found in the ReferenceFrames[] array.
>> >> And this works exactly the same way as before. No functional change yet.
>> >>
>> >> > It can remove the possibility that one picture later used is
>> >> > immediately used to hold a new reference picture in DPB. So based
>> >> > on the above point IMO it is better to find the free_slots through
>> >> > two steps to hold the new reference picture in DPB.
>> >>
>> >> This would only hide further this situation, but OK.
>> >>
>> >> Regards,
>> >> Gwenole.
>> >>
>> >> >> >> + /* Remove obsolete entries from the internal DPB */
>> >> >> >> + for (i = 0, n = 0; i < MAX_GEN_REFERENCE_FRAMES; i++) {
>> >> >> >> + GenFrameStore * const fs = &frame_store[i];
>> >> >> >> + if (fs->surface_id == VA_INVALID_ID || !fs->obj_surface) {
>> >> >> >> + free_slots[n++] = i;
>> >> >> >> continue;
>> >> >> >> + }
>> >> >> >>
>> >> >> >> - assert(frame_store[i].frame_store_id != -1);
>> >> >> >> -
>> >> >> >> - for (j = 0; j < MAX_GEN_REFERENCE_FRAMES; j++) {
>> >> >> >> - VAPictureH264 *ref_pic =
>> >> &pic_param->ReferenceFrames[j];
>> >> >> >> - if (ref_pic->flags & VA_PICTURE_H264_INVALID)
>> >> >> >> + // Find whether the current entry is still a valid
>> >> >> >> + reference
>> >> frame
>> >> >> >> + found = false;
>> >> >> >> + for (j = 0; j <
>> >> >> >> + ARRAY_ELEMS(decode_state->reference_objects);
>> >> j++) {
>> >> >> >> + struct object_surface * const obj_surface =
>> >> >> >> + decode_state->reference_objects[j];
>> >> >> >> + if (!obj_surface)
>> >> >> >> continue;
>> >> >> >> -
>> >> >> >> - if (frame_store[i].surface_id == ref_pic->picture_id) {
>> >> >> >> - found = 1;
>> >> >> >> + if ((found = obj_surface == fs->obj_surface))
>> >> >> >> break;
>> >> >> >> - }
>> >> >> >> }
>> >> >> >>
>> >> >> >> - /* remove it from the internal DPB */
>> >> >> >> + // ... or remove it
>> >> >> >> if (!found) {
>> >> >> >> - frame_store[i].surface_id = VA_INVALID_ID;
>> >> >> >> - frame_store[i].frame_store_id = -1;
>> >> >> >> - frame_store[i].obj_surface = NULL;
>> >> >> >> + fs->surface_id = VA_INVALID_ID;
>> >> >> >> + fs->obj_surface = NULL;
>> >> >> >> + fs->frame_store_id = -1;
>> >> >> >> + free_slots[n++] = i;
>> >> >> >> }
>> >> >> >> }
>> >> >> >> + num_free_slots = n;
>> >> >> >>
>> >> >> >> - for (i = 0; i < MAX_GEN_REFERENCE_FRAMES; i++) {
>> >> >> >> - VAPictureH264 *ref_pic = &pic_param->ReferenceFrames[i];
>> >> >> >> - int found = 0;
>> >> >> >> -
>> >> >> >> - if (ref_pic->flags & VA_PICTURE_H264_INVALID ||
>> >> >> >> - ref_pic->picture_id == VA_INVALID_SURFACE ||
>> >> >> >> - decode_state->reference_objects[i] == NULL)
>> >> >> >> + /* Append the new reference frames */
>> >> >> >> + for (i = 0, n = 0; i <
>> >> >> >> + ARRAY_ELEMS(decode_state->reference_objects);
>> >> i++) {
>> >> >> >> + struct object_surface * const obj_surface =
>> >> >> >> + decode_state->reference_objects[i];
>> >> >> >> + if (!obj_surface)
>> >> >> >> continue;
>> >> >> >>
>> >> >> >> + // Find whether the current frame is not already in
>> >> >> >> + our frame
>> >> store
>> >> >> >> + found = false;
>> >> >> >> for (j = 0; j < MAX_GEN_REFERENCE_FRAMES; j++) {
>> >> >> >> - if (frame_store[j].surface_id == ref_pic->picture_id) {
>> >> >> >> - found = 1;
>> >> >> >> + if ((found = frame_store[j].obj_surface ==
>> >> >> >> + obj_surface))
>> >> >> >> break;
>> >> >> >> - }
>> >> >> >> }
>> >> >> >>
>> >> >> >> - /* add the new reference frame into the internal DPB */
>> >> >> >> + // ... or add it
>> >> >> >> if (!found) {
>> >> >> >> - int frame_idx;
>> >> >> >> - int slot_found;
>> >> >> >> - struct object_surface *obj_surface =
>> >> decode_state->reference_objects[i];
>> >> >> >> -
>> >> >> >> - slot_found = 0;
>> >> >> >> - frame_idx = -1;
>> >> >> >> - /* Find a free frame store index */
>> >> >> >> - for (j = 0; j < MAX_GEN_REFERENCE_FRAMES; j++) {
>> >> >> >> - if (frame_store[j].surface_id == VA_INVALID_ID ||
>> >> >> >> - frame_store[j].obj_surface == NULL) {
>> >> >> >> - frame_idx = j;
>> >> >> >> - slot_found = 1;
>> >> >> >> - break;
>> >> >> >> - }
>> >> >> >> + if (n < num_free_slots) {
>> >> >> >> + GenFrameStore * const fs =
>> >> &frame_store[free_slots[n++]];
>> >> >> >> + fs->surface_id = obj_surface->base.id;
>> >> >> >> + fs->obj_surface = obj_surface;
>> >> >> >> + fs->frame_store_id = fs - frame_store;
>> >> >> >> + }
>> >> >> >> + else {
>> >> >> >> + WARN_ONCE("No free slot found for DPB
>> >> >> >> + reference list!!!\n");
>> >> >> >> }
>> >> >> >> -
>> >> >> >> -
>> >> >> >> - if (slot_found) {
>> >> >> >> - frame_store[j].surface_id = ref_pic->picture_id;
>> >> >> >> - frame_store[j].frame_store_id = frame_idx;
>> >> >> >> - frame_store[j].obj_surface = obj_surface;
>> >> >> >> - } else {
>> >> >> >> - WARN_ONCE("Not free slot for DPB reference
>> >> list!!!\n");
>> >> >> >> - }
>> >> >> >> }
>> >> >> >> }
>> >> >> >> -
>> >> >> >> }
>> >> >> >>
>> >> >> >> void
>> >> >> >
>> >> >> >
>> >> >
>> >> >
>> >> _______________________________________________
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