Date:   Wed, 05 Jun 2019 23:12:52 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Jernej Škrabec <jernej.skrabec@...l.net>,
        Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     wens@...e.org, mchehab@...nel.org, gregkh@...uxfoundation.org,
        linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] media: cedrus: Improve H264 memory efficiency

Hi,

Le lundi 03 juin 2019 à 18:37 +0200, Jernej Škrabec a écrit :
> Dne ponedeljek, 03. junij 2019 ob 14:23:28 CEST je Maxime Ripard napisal(a):
> > On Thu, May 30, 2019 at 11:15:16PM +0200, Jernej Skrabec wrote:
> > > H264 decoder driver preallocated pretty big worst case mv col buffer
> > > pool. It turns out that pool is most of the time much bigger than it
> > > needs to be.
> > > 
> > > Solution implemented here is to allocate memory only if capture buffer
> > > is actually used and only as much as it is really necessary.
> > > 
> > > This is also preparation for 4K video decoding support, which will be
> > > implemented later.
> > 
> > What is it doing exactly to prepare for 4k?
> 
> Well, with that change 4K videos can be actually watched with 256 MiB CMA 
> pool, but I can drop this statement in next version.
> 
> I concentrated on 256 MiB CMA pool, because it's maximum memory size supported 
> by older VPU versions, but I think they don't support 4K decoding. I don't 
> have them, so I can't test that hypothesis.

I think it's a fair goal to try and optimize the CMA pool usage, maybe
it should be presented as that and I guess it's fine to connect that to
4K decoding if you like :)

Either way, I think we should have per-codec framework callbacks for
these kinds of things.

Cheers,

Paul

> > > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > > ---
> > > 
> > >  drivers/staging/media/sunxi/cedrus/cedrus.h   |  4 -
> > >  .../staging/media/sunxi/cedrus/cedrus_h264.c  | 81 +++++++------------
> > >  2 files changed, 28 insertions(+), 57 deletions(-)
> > > 
> > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.h
> > > b/drivers/staging/media/sunxi/cedrus/cedrus.h index
> > > 16c1bdfd243a..fcbbbef65494 100644
> > > --- a/drivers/staging/media/sunxi/cedrus/cedrus.h
> > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus.h
> > > @@ -106,10 +106,6 @@ struct cedrus_ctx {
> > > 
> > >  	union {
> > >  	
> > >  		struct {
> > > 
> > > -			void		*mv_col_buf;
> > > -			dma_addr_t	mv_col_buf_dma;
> > > -			ssize_t		mv_col_buf_field_size;
> > > -			ssize_t		mv_col_buf_size;
> > > 
> > >  			void		*pic_info_buf;
> > >  			dma_addr_t	pic_info_buf_dma;
> > >  			void		*neighbor_info_buf;
> > > 
> > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c index
> > > b2290f98d81a..758fd0049e8f 100644
> > > --- a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > @@ -54,17 +54,14 @@ static void cedrus_h264_write_sram(struct cedrus_dev
> > > *dev,> 
> > >  		cedrus_write(dev, VE_AVC_SRAM_PORT_DATA, *buffer++);
> > >  
> > >  }
> > > 
> > > -static dma_addr_t cedrus_h264_mv_col_buf_addr(struct cedrus_ctx *ctx,
> > > -					      unsigned int 
> position,
> > > +static dma_addr_t cedrus_h264_mv_col_buf_addr(struct cedrus_buffer *buf,
> > > 
> > >  					      unsigned int 
> field)
> > >  
> > >  {
> > > 
> > > -	dma_addr_t addr = ctx->codec.h264.mv_col_buf_dma;
> > > -
> > > -	/* Adjust for the position */
> > > -	addr += position * ctx->codec.h264.mv_col_buf_field_size * 2;
> > > +	dma_addr_t addr = buf->extra_buf_dma;
> > > 
> > >  	/* Adjust for the field */
> > > 
> > > -	addr += field * ctx->codec.h264.mv_col_buf_field_size;
> > > +	if (field)
> > > +		addr += buf->extra_buf_size / 2;
> > > 
> > >  	return addr;
> > >  
> > >  }
> > > 
> > > @@ -76,7 +73,6 @@ static void cedrus_fill_ref_pic(struct cedrus_ctx *ctx,
> > > 
> > >  				struct cedrus_h264_sram_ref_pic 
> *pic)
> > >  
> > >  {
> > >  
> > >  	struct vb2_buffer *vbuf = &buf->m2m_buf.vb.vb2_buf;
> > > 
> > > -	unsigned int position = buf->codec.h264.position;
> > > 
> > >  	pic->top_field_order_cnt = cpu_to_le32(top_field_order_cnt);
> > >  	pic->bottom_field_order_cnt = cpu_to_le32(bottom_field_order_cnt);
> > > 
> > > @@ -84,10 +80,8 @@ static void cedrus_fill_ref_pic(struct cedrus_ctx *ctx,
> > > 
> > >  	pic->luma_ptr = cpu_to_le32(cedrus_buf_addr(vbuf, &ctx->dst_fmt, 
> 0));
> > >  	pic->chroma_ptr = cpu_to_le32(cedrus_buf_addr(vbuf, &ctx->dst_fmt, 
> 1));
> > > -	pic->mv_col_top_ptr =
> > > -		cpu_to_le32(cedrus_h264_mv_col_buf_addr(ctx, position, 
> 0));
> > > -	pic->mv_col_bot_ptr =
> > > -		cpu_to_le32(cedrus_h264_mv_col_buf_addr(ctx, position, 
> 1));
> > > +	pic->mv_col_top_ptr = cpu_to_le32(cedrus_h264_mv_col_buf_addr(buf, 
> 0));
> > > +	pic->mv_col_bot_ptr = cpu_to_le32(cedrus_h264_mv_col_buf_addr(buf, 
> 1));
> > >  }
> > >  
> > >  static void cedrus_write_frame_list(struct cedrus_ctx *ctx,
> > > 
> > > @@ -142,6 +136,28 @@ static void cedrus_write_frame_list(struct cedrus_ctx
> > > *ctx,> 
> > >  	output_buf = vb2_to_cedrus_buffer(&run->dst->vb2_buf);
> > >  	output_buf->codec.h264.position = position;
> > > 
> > > +	if (!output_buf->extra_buf_size) {
> > > +		const struct v4l2_ctrl_h264_sps *sps = run->h264.sps;
> > > +		unsigned int field_size;
> > > +
> > > +		field_size = DIV_ROUND_UP(ctx->src_fmt.width, 16) *
> > > +			DIV_ROUND_UP(ctx->src_fmt.height, 16) * 16;
> > > +		if (!(sps->flags & 
> V4L2_H264_SPS_FLAG_DIRECT_8X8_INFERENCE))
> > > +			field_size = field_size * 2;
> > > +		if (!(sps->flags & V4L2_H264_SPS_FLAG_FRAME_MBS_ONLY))
> > > +			field_size = field_size * 2;
> > > +
> > > +		output_buf->extra_buf_size = field_size * 2;
> > > +		output_buf->extra_buf =
> > > +			dma_alloc_coherent(dev->dev,
> > > +					   output_buf-
> > extra_buf_size,
> > > +					   &output_buf-
> > extra_buf_dma,
> > > +					   GFP_KERNEL);
> > > +
> > > +		if (!output_buf->extra_buf)
> > > +			output_buf->extra_buf_size = 0;
> > > +	}
> > > +
> > 
> > That also means that instead of allocating that buffer exactly once,
> > you now allocate it for each output buffer?
> 
> It's not completely the same. I'm allocating multiple times, yes, but much 
> smaller chunks and only if needed.
> 
> Still, this slight overhead happens only when buffer is used for the first time. 
> When buffer is reused, this MV buffer is also reused.
> 
> > I guess that it will cleaned up by your previous patch at
> > buffer_cleanup time, so after it's no longer a reference frame?
> 
> Yes, it will be deallocated in buffer_cleanup, but only after capture buffers 
> are freed, which usually happens when device file descriptor is closed.
> 
> Buffers which holds reference frames are later reused, together with it's MV 
> buffer, so there's no overhead.
> 
> > What is the average memory usage before, and after that change during
> > a playback, and what is the runtime cost of doing it multiple times
> > instead of once?
> 
> As I already said, overhead is present only when buffer is used for the first 
> time, which is not ideal, but allows to calculate minimal buffer size needed 
> and even doesn't allocate anything if capture buffer is not used at all.
> 
> I didn't collect any exact numbers, but with this change I can play H264 and 
> HEVC (with similar modification) 4K video samples with 256 MiB CMA pool. 
> Without this change, it's not really possible. You can argue "but what if 4K 
> video use 16 reference frames", then yes, only solution is to increase CMA 
> pool, but why reserve extra memory which will never be used?
> 
> I've been using this optimization for past ~6 month with no issues noticed. If 
> you feel better, I can change this to be a bit conservative and allocate MV 
> buffer when buffer_init is called. This will consume a bit more memory as SPS is 
> not available at that time (worst case buffer size estimation), but it still 
> won't allocate MV buffers for unallocated capture frames.
> 
> Best regards,
> Jernej
> 
> 

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