Re: [PATCH v6 2/2] media: usb: pwc: Don't use coherent DMA buffers for ISO transfer

From: Steven Rostedt
Date: Wed Dec 12 2018 - 08:56:29 EST


Can someone please take this patch or at least say what's wrong with it
if you have a problem?

Matwey has been patiently pinging us once every other week for over a
month asking for a reply. I've already given my Reviewed-by from a
tracing perspective.

Ignoring patches is not a friendly gesture.

-- Steve


On Wed, 12 Dec 2018 16:07:38 +0300
"Matwey V. Kornilov" <matwey.kornilov@xxxxxxxxx> wrote:

> ÐÑ, 30 ÐÐÑÐ. 2018 Ð. Ð 15:20, Matwey V. Kornilov <matwey.kornilov@xxxxxxxxx>:
> >
> > ÑÑ, 21 ÐÐÑÐ. 2018 Ð. Ð 21:15, Matwey V. Kornilov <matwey.kornilov@xxxxxxxxx>:
> > >
> > > ÐÑ, 9 ÐÐÑÐ. 2018 Ð. Ð 22:03, 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 = ( 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 <matwey@xxxxxxxxxx>
> > >
> > > Ping
> >
> > Ping
>
> Ping
>
> >
> > >
> > > > ---
> > > > 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 53c111bd5a22..a81fb319b339 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
> > > > @@ -352,6 +383,11 @@ 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);
> > > >
> > > > @@ -428,16 +464,15 @@ 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 +523,16 @@ 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
> >
> >
> >
> > --
> > With best regards,
> > Matwey V. Kornilov
>
>
>