Re: [PATCH] media: Fix a UVC performance problem on systems with non-coherent DMA.
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Date: 2011-08-26 09:23:14
Hi Al, Thanks for the patch. On Thursday 18 August 2011 15:28:29 Al Cooper wrote:
The UVC driver uses usb_alloc_coherent() to allocate DMA data buffers. On systems without coherent DMA this ends up allocating buffers in uncached memory. The subsequent memcpy's done to coalesce the DMA chunks into contiguous buffers then run VERY slowly. On a MIPS test system the memcpy is about 200 times slower. This issue prevents the system from keeping up with 720p YUYV data at 10fps. The following patch uses kmalloc to alloc the DMA buffers instead of uab_alloc_coherent on systems without coherent DMA. With this patch the system was easily able to keep up with 720p at 10fps. Signed-off-by: Al Cooper <alcooperx@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> I will push it to v3.2.
quoted hunk ↗ jump to hunk
--- drivers/media/video/uvc/uvc_video.c | 18 +++++++++++++++++- 1 files changed, 17 insertions(+), 1 deletions(-)diff --git a/drivers/media/video/uvc/uvc_video.cb/drivers/media/video/uvc/uvc_video.c index 4999479..30c18b4 100644--- a/drivers/media/video/uvc/uvc_video.c +++ b/drivers/media/video/uvc/uvc_video.c@@ -790,8 +790,12 @@ static void uvc_free_urb_buffers(struct uvc_streaming*stream) for (i = 0; i < UVC_URBS; ++i) { if (stream->urb_buffer[i]) { +#ifndef CONFIG_DMA_NONCOHERENT usb_free_coherent(stream->dev->udev, stream->urb_size, stream->urb_buffer[i], stream->urb_dma[i]); +#else + kfree(stream->urb_buffer[i]); +#endif stream->urb_buffer[i] = NULL; } }@@ -831,9 +835,15 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming*stream, for (; npackets > 1; npackets /= 2) { for (i = 0; i < UVC_URBS; ++i) { stream->urb_size = psize * npackets; +#ifndef CONFIG_DMA_NONCOHERENT stream->urb_buffer[i] = usb_alloc_coherent( stream->dev->udev, stream->urb_size, gfp_flags | __GFP_NOWARN, &stream->urb_dma[i]); +#else + stream->urb_buffer[i] = + kmalloc(stream->urb_size, gfp_flags | __GFP_NOWARN); +#endif + if (!stream->urb_buffer[i]) { uvc_free_urb_buffers(stream); break;@@ -908,10 +918,14 @@ static int uvc_init_video_isoc(struct uvc_streaming*stream, urb->context = stream; urb->pipe = usb_rcvisocpipe(stream->dev->udev, ep->desc.bEndpointAddress); +#ifndef CONFIG_DMA_NONCOHERENT urb->transfer_flags = URB_ISO_ASAP | URB_NO_TRANSFER_DMA_MAP; + urb->transfer_dma = stream->urb_dma[i]; +#else + urb->transfer_flags = URB_ISO_ASAP; +#endif urb->interval = ep->desc.bInterval; urb->transfer_buffer = stream->urb_buffer[i]; - urb->transfer_dma = stream->urb_dma[i]; urb->complete = uvc_video_complete; urb->number_of_packets = npackets; urb->transfer_buffer_length = size;@@ -969,8 +983,10 @@ static int uvc_init_video_bulk(struct uvc_streaming*stream, usb_fill_bulk_urb(urb, stream->dev->udev, pipe, stream->urb_buffer[i], size, uvc_video_complete, stream); +#ifndef CONFIG_DMA_NONCOHERENT urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP; urb->transfer_dma = stream->urb_dma[i]; +#endif stream->urb[i] = urb; }
-- Regards, Laurent Pinchart