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Message-ID: <CAJs94EYmRpUSnxzyt-8bdSwp3WgvOuqpt4b55wKQ41jDynFceg@mail.gmail.com>
Date: Fri, 30 Nov 2018 15:20:57 +0300
From: "Matwey V. Kornilov" <matwey.kornilov@...il.com>
To: Linux Media Mailing List <linux-media@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Cc: Tomasz Figa <tfiga@...omium.org>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Alan Stern <stern@...land.harvard.edu>,
Ezequiel Garcia <ezequiel@...labora.com>,
Hans de Goede <hdegoede@...hat.com>,
Hans Verkuil <hverkuil@...all.nl>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
Mike Isely <isely@...ox.com>,
Bhumika Goyal <bhumirks@...il.com>,
Colin King <colin.king@...onical.com>,
Kieran Bingham <kieran.bingham@...asonboard.com>,
keiichiw@...omium.org
Subject: Re: [PATCH v6 2/2] media: usb: pwc: Don't use coherent DMA buffers
for ISO transfer
ср, 21 нояб. 2018 г. в 21:15, Matwey V. Kornilov <matwey.kornilov@...il.com>:
>
> пт, 9 нояб. 2018 г. в 22:03, Matwey V. Kornilov <matwey@....msu.ru>:
> >
> > 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@....msu.ru>
>
> 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
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