19 Nov 2021, 17:24 by softwo...@hotmail.com:
>
>
>> -----Original Message-----
>> From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of
>> Xiang, Haihao
>> Sent: Monday, October 18, 2021 6:48 AM
>> To: ffmpeg-devel@ffmpeg.org
>> Subject: Re: [FFmpeg-devel] [PATCH v3 1/1] avutils/hwcontext: When
>> deriving a hwdevice, search for existing device in both directions
>>
>> On Mon, 2021-10-11 at 04:19 +0000, Soft Works wrote:
>> > The test /libavutil/tests/hwdevice checks that when deriving a
>> device
>> > from a source device and then deriving back to the type of the
>> source
>> > device, the result is matching the original source device, i.e. the
>> > derivation mechanism doesn't create a new device in this case.
>> >
>> > Previously, this test was usually passed, but only due to two
>> different
>> > kind of flaws:
>> >
>> > 1. The test covers only a single level of derivation (and back)
>> >
>> > It derives device Y from device X and then Y back to the type of X
>> and
>> > checks whether the result matches X.
>> >
>> > What it doesn't check for, are longer chains of derivation like:
>> >
>> > CUDA1 > OpenCL2 > CUDA3 and then back to OpenCL4
>> >
>> > In that case, the second derivation returns the first device (CUDA3
>> ==
>> > CUDA1), but when deriving OpenCL4, hwcontext.c was creating a new
>> > OpenCL4 context instead of returning OpenCL2, because there was no
>> link
>> > from CUDA1 to OpenCL2 (only backwards from OpenCL2 to CUDA1)
>> >
>> > If the test would check for two levels of derivation, it would have
>> > failed.
>> >
>> > This patch fixes those (yet untested) cases by introducing forward
>> > references (derived_device) in addition to the existing back
>> references
>> > (source_device).
>> >
>> > 2. hwcontext_qsv didn't properly set the source_device
>> >
>> > In case of QSV, hwcontext_qsv creates a source context internally
>> > (vaapi, dxva2 or d3d11va) without calling
>> av_hwdevice_ctx_create_derived
>> > and without setting source_device.
>> >
>> > This way, the hwcontext test ran successful, but what practically
>> > happened, was that - for example - deriving vaapi from qsv didn't
>> return
>> > the original underlying vaapi device and a new one was created
>> instead:
>> > Exactly what the test is intended to detect and prevent. It just
>> > couldn't do so, because the original device was hidden (= not set
>> as the
>> > source_device of the QSV device).
>> >
>> > This patch properly makes these setting and fixes all derivation
>> > scenarios.
>> >
>> > (at a later stage, /libavutil/tests/hwdevice should be extended to
>> check
>> > longer derivation chains as well)
>> >
>> > Signed-off-by: softworkz <softwo...@hotmail.com>
>> > ---
>> > v3: avoid double-release as suggested by Haihao
>> >
>> > libavutil/hwcontext.c | 38
>> ++++++++++++++++++++++++++++++++++
>> > libavutil/hwcontext.h | 1 +
>> > libavutil/hwcontext_internal.h | 6 ++++++
>> > libavutil/hwcontext_qsv.c | 16 ++++++++++----
>> > 4 files changed, 57 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/libavutil/hwcontext.c b/libavutil/hwcontext.c
>> > index 31c7840dba..1a50635018 100644
>> > --- a/libavutil/hwcontext.c
>> > +++ b/libavutil/hwcontext.c
>> > @@ -122,6 +122,7 @@ static const AVClass hwdevice_ctx_class = {
>> > static void hwdevice_ctx_free(void *opaque, uint8_t *data)
>> > {
>> > AVHWDeviceContext *ctx = (AVHWDeviceContext*)data;
>> > + int i;
>> >
>> > /* uninit might still want access the hw context and the user
>> > * free() callback might destroy it, so uninit has to be
>> called first */
>> > @@ -132,6 +133,8 @@ static void hwdevice_ctx_free(void *opaque,
>> uint8_t *data)
>> > ctx->free(ctx);
>> >
>> > av_buffer_unref(&ctx->internal->source_device);
>> > + for (i = 0; i < AV_HWDEVICE_TYPE_NB; i++)
>> > + av_buffer_unref(&ctx->internal->derived_devices[i]);
>> >
>> > av_freep(&ctx->hwctx);
>> > av_freep(&ctx->internal->priv);
>> > @@ -643,6 +646,26 @@ fail:
>> > return ret;
>> > }
>> >
>> > +static AVBufferRef* find_derived_hwdevice_ctx(AVBufferRef
>> *src_ref, enum
>> > AVHWDeviceType type)
>> > +{
>> > + AVBufferRef *tmp_ref;
>> > + AVHWDeviceContext *src_ctx;
>> > + int i;
>> > +
>> > + src_ctx = (AVHWDeviceContext*)src_ref->data;
>> > + if (src_ctx->type == type)
>> > + return src_ref;
>> > +
>> > + for (i = 0; i < AV_HWDEVICE_TYPE_NB; i++)
>> > + if (src_ctx->internal->derived_devices[i]) {
>> > + tmp_ref = find_derived_hwdevice_ctx(src_ctx->internal-
>> > >derived_devices[i], type);
>> > + if (tmp_ref)
>> > + return tmp_ref;
>> > + }
>> > +
>> > + return NULL;
>> > +}
>> > +
>> > int av_hwdevice_ctx_create_derived_opts(AVBufferRef **dst_ref_ptr,
>> > enum AVHWDeviceType type,
>> > AVBufferRef *src_ref,
>> > @@ -666,6 +689,16 @@ int
>> av_hwdevice_ctx_create_derived_opts(AVBufferRef
>> > **dst_ref_ptr,
>> > tmp_ref = tmp_ctx->internal->source_device;
>> > }
>> >
>> > + tmp_ref = find_derived_hwdevice_ctx(src_ref, type);
>> > + if (tmp_ref) {
>> > + dst_ref = av_buffer_ref(tmp_ref);
>> > + if (!dst_ref) {
>> > + ret = AVERROR(ENOMEM);
>> > + goto fail;
>> > + }
>> > + goto done;
>> > + }
>> > +
>> > dst_ref = av_hwdevice_ctx_alloc(type);
>> > if (!dst_ref) {
>> > ret = AVERROR(ENOMEM);
>> > @@ -687,6 +720,11 @@ int
>> av_hwdevice_ctx_create_derived_opts(AVBufferRef
>> > **dst_ref_ptr,
>> > ret = AVERROR(ENOMEM);
>> > goto fail;
>> > }
>> > + tmp_ctx->internal->derived_devices[type] =
>> > av_buffer_ref(dst_ref);
>> > + if (!tmp_ctx->internal->derived_devices[type]) {
>> > + ret = AVERROR(ENOMEM);
>> > + goto fail;
>> > + }
>> > ret = av_hwdevice_ctx_init(dst_ref);
>> > if (ret < 0)
>> > goto fail;
>> > diff --git a/libavutil/hwcontext.h b/libavutil/hwcontext.h
>> > index 04d19d89c2..56077963e6 100644
>> > --- a/libavutil/hwcontext.h
>> > +++ b/libavutil/hwcontext.h
>> > @@ -37,6 +37,7 @@ enum AVHWDeviceType {
>> > AV_HWDEVICE_TYPE_OPENCL,
>> > AV_HWDEVICE_TYPE_MEDIACODEC,
>> > AV_HWDEVICE_TYPE_VULKAN,
>> > + AV_HWDEVICE_TYPE_NB, ///< number of hw device types
>> > };
>> >
>> > typedef struct AVHWDeviceInternal AVHWDeviceInternal;
>> > diff --git a/libavutil/hwcontext_internal.h
>> b/libavutil/hwcontext_internal.h
>> > index e6266494ac..f6fb67c491 100644
>> > --- a/libavutil/hwcontext_internal.h
>> > +++ b/libavutil/hwcontext_internal.h
>> > @@ -109,6 +109,12 @@ struct AVHWDeviceInternal {
>> > * context it was derived from.
>> > */
>> > AVBufferRef *source_device;
>> > +
>> > + /**
>> > + * An array of reference to device contexts which
>> > + * were derived from this device.
>> > + */
>> > + AVBufferRef *derived_devices[AV_HWDEVICE_TYPE_NB];
>> > };
>> >
>> > struct AVHWFramesInternal {
>> > diff --git a/libavutil/hwcontext_qsv.c b/libavutil/hwcontext_qsv.c
>> > index c18747f7eb..7b559e2b47 100644
>> > --- a/libavutil/hwcontext_qsv.c
>> > +++ b/libavutil/hwcontext_qsv.c
>> > @@ -223,7 +223,7 @@ static void qsv_frames_uninit(AVHWFramesContext
>> *ctx)
>> > av_buffer_unref(&s->child_frames_ref);
>> > }
>> >
>> > -static void qsv_pool_release_dummy(void *opaque, uint8_t *data)
>> > +static void qsv_release_dummy(void *opaque, uint8_t *data)
>> > {
>> > }
>> >
>> > @@ -236,9 +236,9 @@ static AVBufferRef *qsv_pool_alloc(void
>> *opaque, size_t
>> > size)
>> > if (s->nb_surfaces_used < hwctx->nb_surfaces) {
>> > s->nb_surfaces_used++;
>> > av_buffer_create((uint8_t*)(s->handle_pairs_internal + s-
>> > >nb_surfaces_used - 1),
>> > - sizeof(*s->handle_pairs_internal),
>> > qsv_pool_release_dummy, NULL, 0);
>> > + sizeof(*s->handle_pairs_internal),
>> > qsv_release_dummy, NULL, 0);
>> > return av_buffer_create((uint8_t*)(s->surfaces_internal +
>> s-
>> > >nb_surfaces_used - 1),
>> > - sizeof(*hwctx->surfaces),
>> > qsv_pool_release_dummy, NULL, 0);
>> > + sizeof(*hwctx->surfaces),
>> qsv_release_dummy,
>> > NULL, 0);
>> > }
>> >
>> > return NULL;
>> > @@ -1528,8 +1528,16 @@ static int
>> qsv_device_create(AVHWDeviceContext *ctx,
>> > const char *device,
>> > child_device = (AVHWDeviceContext*)priv->child_device_ctx-
>> >data;
>> >
>> > impl = choose_implementation(device, child_device_type);
>> > + ret = qsv_device_derive_from_child(ctx, impl, child_device,
>> 0);
>> > + if (ret >= 0) {
>> > + ctx->internal->source_device = av_buffer_ref(priv-
>> >child_device_ctx);
>> > + child_device->internal->derived_devices[ctx->type] =
>> > av_buffer_create((uint8_t*)ctx, sizeof(*ctx), qsv_release_dummy,
>> ctx, 0);
>> > + if (!child_device->internal->derived_devices[ctx->type]) {
>> > + return AVERROR(ENOMEM);
>> > + }
>> > + }
>> >
>> > - return qsv_device_derive_from_child(ctx, impl, child_device,
>> 0);
>> > + return ret;
>> > }
>> >
>> > const HWContextType ff_hwcontext_type_qsv = {
>>
>> LGTM,
>>
>> -Haihao
>>
>
> @Hendrik: You had some concerns regarding the initial version, which I have
> addressed. Could you please check whether it looks good to you now?
>
> @Wenbin, @Xu: Could you confirm whether this patch eliminates the need for
> the other workarounds you currently have in place on cartwheel?
>
> For making things work like "qsv->vaapi->vulkan->vaapi->qsv pipeline"
> (https://github.com/intel-media-ci/cartwheel-ffmpeg/commit/564169857f552d585f827dbc1387b6abf6526139)
>
> @Lynne, @haasm, @Wu: This patch might also be relevant for working Vulkan
> context derivation as it prevents the creation of new hardware contexts
> in non-trivial derivation chains.
>
> I think this patch is essential for properly working with derived hw contexts
> and I'd be glad to hear some more thoughts about it.
>
This is indeed relevant to working Vulkan derivation, especially with VAAPI.
I've hit this limitation before.
I've reviewed the patch, it looks good, except a small coding style nit,
do not put brackets on one-line statements, look at `if
(!child_device->internal->derived_devices[ctx->type]) {`,
and you should also add a comment to AV_HWDEVICE_TYPE_NB where
it says "Not part of the API, do not use.".
Apart from that, I think if no one responds in a day or two, you should
push it.
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