Intel's Ivy Bridge: An HTPC Perspective

Advanced HTPC users adopt specialized renderers such as madVR which provide better quality when rendering videos. Unlike the standard EVR-CP (Enhanced Video Renderer-Custom Presenter) which doesn't stress the GPU much, renderers like madVR are very GPU-intensive. This has often been the sole reason for many HTPC users to go in for NVIDIA or AMD cards for their HTPC. Traditionally, Intel GPUs have lacked the performance necessary for madVR to function properly (particularly with high definition streams). We did some experiments to check whether Ivy Bridge managed some improvements.

Using our testbed with the 4 GB of DRAM running at DDR3-1333 9-9-9-24, we took one clip each of 1080i60 H.264, 1080i60  VC-1, 1080i60 MPEG-2, 576i50 H.264, 480i60 MPEG-2 and 1080p60 H.264. We tabulated the CPU and GPU usage using various combinations of decoders and renderers. It is quite obvious that using madVR tends to drive up the CPU usage compared to pure DXVA mode (with EVR-CP renderer). This is because the CPU needs to copy back the data to the system memory for madVR to execute the GPU algorithms. A single star against the GPU usage indicates between 5 - 10 dropped frames in a 3 minute duration. Double stars indicate that the number of dropped frames was high and that the dropping of the frames was clearly visible to the naked eye.

With DDR3-1333, it is evident that 1080i60 streams just can't get processed through madVR without becoming unwatchable. Memory bandwidth constraints are quite problematic for madVR. So, we decided to overclock the memory a bit, and got the G.Skill ECO RAM running at DDR3-1600 without affecting the latency. Of course, we made sure that the system was stable running Prime95 for a couple of hours before proceeding with the testing. With the new memory configuration, we see that the GPU usage improved considerably, and we were able to get madVR to render even 1080p60 videos without dropping frames.

However, the 5 - 10 dropped frames in the 1080i60 MPEG-2 clip continued to bother me. I tried to overclock G.Skill's DDR3-1600 rated DRAM, but was unable to reach DDR3-1800 without sacrificing latency. With a working configuration of DDR3-1800 12-12-12-32, I repeated the tests, but found that the figures didn't improve.

My inference is that a low memory latency is as important as high bandwidth for madVR to function effectively. I am positive that with a judicious choice of DRAM, it is possible to get madVR functioning flawlessly with the Ivy Bridge platofrm. Of course, more testing needs to be done with other algorithms, but the outlook is quite positive.

In all this talk about madVR, let us not forget the efficient QuickSync / native DXVA2 decoders in combination with EVR-CP. With low CPU usage and moderate GPU usage, these combinations deliver satisfactory results for the general HTPC crowd.