From: "Matwey V. Kornilov" DMA cocherency slows the transfer down on systems without hardware coherent DMA. Instead we use noncocherent DMA memory and explicit sync at data receive handler. Based on previous commit the following performance benchmarks have been carried out. Average memcpy() data transfer rate (rate) and handler completion time (time) have been measured when running video stream at 640x480 resolution at 10fps. x86_64 based system (Intel Core i5-3470). This platform has hardware coherent DMA support and proposed change doesn't make big difference here. * kmalloc: rate = (2.0 +- 0.4) GBps time = (5.0 +- 3.0) usec * usb_alloc_coherent: rate = (3.4 +- 1.2) GBps time = (3.5 +- 3.0) usec We see that the measurements agree within error ranges in this case. So theoretically predicted performance downgrade cannot be reliably measured here. armv7l based system (TI AM335x BeagleBone Black @ 300MHz). This platform has no hardware coherent DMA support. DMA coherence is implemented via disabled page caching that slows down memcpy() due to memory controller behaviour. * kmalloc: rate = ( 94 +- 4) MBps time = (101 +- 4) usec * usb_alloc_coherent: rate = (28.1 +- 0.1) MBps time = (341 +- 2) usec Note, that quantative difference leads (this commit leads to 3.3 times acceleration) to qualitative behavior change in this case. As it was stated before, the video stream cannot be successfully received at AM335x platforms with MUSB based USB host controller due to performance issues [1]. [1] https://www.spinics.net/lists/linux-usb/msg165735.html Signed-off-by: Matwey V. Kornilov Reviewed-by: Laurent Pinchart Signed-off-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab References: boo#1054610 Patch-mainline: v5.1-rc1 Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git Git-commit: 1161db6776bd1c35257e1e362e91bcb1b3fe4347 Signed-off-by: Matwey V. Kornilov --- drivers/media/usb/pwc/pwc-if.c | 62 +++++++++++++++++++++++++++++++++--------- 1 file changed, 49 insertions(+), 13 deletions(-) diff --git a/drivers/media/usb/pwc/pwc-if.c b/drivers/media/usb/pwc/pwc-if.c index e94b3b22eed3..8733720d6198 100644 --- a/drivers/media/usb/pwc/pwc-if.c +++ b/drivers/media/usb/pwc/pwc-if.c @@ -159,6 +159,32 @@ static struct video_device pwc_template = { /***************************************************************************/ /* Private functions */ +static void *pwc_alloc_urb_buffer(struct device *dev, + size_t size, dma_addr_t *dma_handle) +{ + void *buffer = kmalloc(size, GFP_KERNEL); + + if (!buffer) + return NULL; + + *dma_handle = dma_map_single(dev, buffer, size, DMA_FROM_DEVICE); + if (dma_mapping_error(dev, *dma_handle)) { + kfree(buffer); + return NULL; + } + + return buffer; +} + +static void pwc_free_urb_buffer(struct device *dev, + size_t size, + void *buffer, + dma_addr_t dma_handle) +{ + dma_unmap_single(dev, dma_handle, size, DMA_FROM_DEVICE); + kfree(buffer); +} + static struct pwc_frame_buf *pwc_get_next_fill_buf(struct pwc_device *pdev) { unsigned long flags = 0; @@ -305,6 +331,11 @@ static void pwc_isoc_handler(struct urb *urb) /* Reset ISOC error counter. We did get here, after all. */ pdev->visoc_errors = 0; + dma_sync_single_for_cpu(&urb->dev->dev, + urb->transfer_dma, + urb->transfer_buffer_length, + DMA_FROM_DEVICE); + /* vsync: 0 = don't copy data 1 = sync-hunt 2 = synched @@ -351,6 +382,11 @@ static void pwc_isoc_handler(struct urb *urb) pdev->vlast_packet_size = flen; } + dma_sync_single_for_device(&urb->dev->dev, + urb->transfer_dma, + urb->transfer_buffer_length, + DMA_FROM_DEVICE); + handler_end: trace_pwc_handler_exit(urb, pdev); @@ -427,16 +463,15 @@ static int pwc_isoc_init(struct pwc_device *pdev) urb->dev = udev; urb->pipe = usb_rcvisocpipe(udev, pdev->vendpoint); urb->transfer_flags = URB_ISO_ASAP | URB_NO_TRANSFER_DMA_MAP; - urb->transfer_buffer = usb_alloc_coherent(udev, - ISO_BUFFER_SIZE, - GFP_KERNEL, - &urb->transfer_dma); + urb->transfer_buffer_length = ISO_BUFFER_SIZE; + urb->transfer_buffer = pwc_alloc_urb_buffer(&udev->dev, + urb->transfer_buffer_length, + &urb->transfer_dma); if (urb->transfer_buffer == NULL) { PWC_ERROR("Failed to allocate urb buffer %d\n", i); pwc_isoc_cleanup(pdev); return -ENOMEM; } - urb->transfer_buffer_length = ISO_BUFFER_SIZE; urb->complete = pwc_isoc_handler; urb->context = pdev; urb->start_frame = 0; @@ -487,15 +522,16 @@ static void pwc_iso_free(struct pwc_device *pdev) /* Freeing ISOC buffers one by one */ for (i = 0; i < MAX_ISO_BUFS; i++) { - if (pdev->urbs[i]) { + struct urb *urb = pdev->urbs[i]; + + if (urb) { PWC_DEBUG_MEMORY("Freeing URB\n"); - if (pdev->urbs[i]->transfer_buffer) { - usb_free_coherent(pdev->udev, - pdev->urbs[i]->transfer_buffer_length, - pdev->urbs[i]->transfer_buffer, - pdev->urbs[i]->transfer_dma); - } - usb_free_urb(pdev->urbs[i]); + if (urb->transfer_buffer) + pwc_free_urb_buffer(&urb->dev->dev, + urb->transfer_buffer_length, + urb->transfer_buffer, + urb->transfer_dma); + usb_free_urb(urb); pdev->urbs[i] = NULL; } } -- 2.16.4 -- To unsubscribe, e-mail: opensuse-kernel+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-kernel+owner@opensuse.org