Hi, I posted this on linux-uvc-devel, but was told the data transfer part is handled by the USB driver. I am running 3.17.8 kernel with DMA enabled on TI DM3730 (Gumstix Overo Firestorm-P COM). When streaming video frames in mmap or userptr mode, I am seeing very high CPU usage, up to 70%. This CPU usage is reported to be in software interrupts. The captured frames are NOT corrupted. Interestingly, when running 3.5 kernel, with DMA enabled as well, the CPU usage is 30% and it is reported to be mostly in the user space. So, it guess it suggests PIO not DMA is actually used here. Neither of these results are satisfactory, I hoped DMA would take care of the data transfer and the CPU resources would be available to run data processing. I used the video capture example from the V4L2 API documentation. This behavior was tested and observed for two different cameras, one of them working in isochronous mode, the other working in bulk mode. Interrupts showing activity during the streaming are: omap-dma-engine, ehci_hcd:usb1. I also ran another test with very low resolution and fps settings, 160x90 5ps YUV422. In that case, on 3.5 kernel, CPU usage was very low. However, on 3.17.8 kernel, it was still similar as before, around 60% and all in software interrupts; it was dropping to zero intermittently this time. Perhaps, the problem is somewhere in the interaction between the UVC driver and the DMA or USB driver. As far as I understand, the UVC driver uses vmalloc(), which, again AFAIU, is not ideal for DMA transfers. Is this known to work on other similar platforms? I am aware this is a somewhat vague description unfortunately, but I am not sure what other detail would be helpful. UVC debugging messages do not show anything unusual. Beyond that, debugging these drivers on my own exceeds my expertise, so I will welcome any suggestions. There is also the following error message from EDMA, I do not think it is related though. [ 0.557342] edma-dma-engine edma-dma-engine.0: Can't allocate PaRAM dummy slot [ 0.557434] edma-dma-engine: probe of edma-dma-engine.0 failed with error -22 Thanks, Tom -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
