вт, 21 авг. 2018 г. в 20:06, Matwey V. Kornilov <matwey@xxxxxxxxxx>: > > 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 = (114 +- 5) MBps > time = (84 +- 4) usec > * usb_alloc_coherent: rate = (28.1 +- 0.1) MBps > time = (341 +- 2) usec > > Note, that quantative difference leads (this commit leads to 4 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 <matwey@xxxxxxxxxx> Ping > --- > drivers/media/usb/pwc/pwc-if.c | 57 ++++++++++++++++++++++++++++++++---------- > 1 file changed, 44 insertions(+), 13 deletions(-) > > diff --git a/drivers/media/usb/pwc/pwc-if.c b/drivers/media/usb/pwc/pwc-if.c > index 72d2897a4b9f..1360722ab423 100644 > --- a/drivers/media/usb/pwc/pwc-if.c > +++ b/drivers/media/usb/pwc/pwc-if.c > @@ -159,6 +159,32 @@ static const 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; > @@ -306,6 +332,11 @@ 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 > @@ -428,16 +459,15 @@ 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; > @@ -488,15 +518,16 @@ 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 > -- With best regards, Matwey V. Kornilov
