[Libva] performances question with libva on i5 sandy bridge

[Gilles Chanteperdrix]

Hi,

I am testing libva with ffmpeg on Linux to decode h264 video. 
Linux version is 3.4.29 
FFmpeg version is 2.5.3 
Mesa version is 10.4.0 
libdrm version is 2.4.58 
libva version is 1.5.0

>From what I could gather from the documentation and examples, using
vaDeriveImage should be preferred if it is available. However, I
have compared, with top, the CPU consumed, and I observe that the
following code:

#ifdef USE_VADERIVEIMAGE
	vrc = vaDeriveImage(ctx->display, buf->surface_id, &va_image);
	CHECK_VASTATUS(vrc, "vaDeriveImage");
#else
	vrc = vaGetImage(ctx->display, buf->surface_id,
			0, 0, cctx->coded_width, cctx->coded_height,
			va_image.image_id);
	CHECK_VASTATUS(vrc, "vaGetImage");
#endif

	vrc = vaMapBuffer(ctx->display, va_image.buf, &data);
	CHECK_VASTATUS(vrc, "vaMapBuffer");

	memcpy(f->img[0], data + va_image.offsets[0],
		va_image.pitches[0] * cctx->coded_height);
	memcpy(f->img[1], data + va_image.offsets[1],
		va_image.pitches[1] * cctx->coded_height / 2);

	vrc = vaUnmapBuffer(ctx->display, va_image.buf);
	CHECK_VASTATUS(vrc, "vaUnmapBuffer");

#ifdef USE_VADERIVEIMAGE
	vrc = vaDestroyImage(ctx->display, va_image.image_id);
	CHECK_VASTATUS(vrc, "vaDestroyImage");
#endif

Results in a higher cpu consumption if compiled with
USE_VADERIVEIMAGE. Is this normal, or is there something I am doing
wrong? I can provide the complete code if needed.

As a second question, is there a function allowing to copy image
from a VA surface to custom pointers? I see I can build a buffer
with some custom pointers, but I do not see how to copy a surface to
them. I would like something like the inverse operation of
vaRenderPicture.

Thanks in advance.
Regards.

-- 
					    Gilles.