Re: [PATCH v2 6/6] media: uvcvideo: Use dma_alloc_noncontiguous API

[Laurent Pinchart]

Hi Ricardo,

On Fri, Mar 12, 2021 at 11:15:46PM +0100, Ricardo Ribalda Delgado wrote:
> On Fri, Mar 12, 2021 at 10:19 PM Laurent Pinchart wrote:
> > On Fri, Mar 12, 2021 at 01:57:09PM +0100, Ricardo Ribalda wrote:
> > > On architectures where there is no coherent caching such as ARM use the
> > > dma_alloc_noncontiguous API and handle manually the cache flushing using
> > > dma_sync_sgtable().
> >
> > You're actually switching to dma_alloc_noncontiguous() unconditionally,
> > not only on those architectures :-) Do I assume correctly that
> > dma_alloc_noncontiguous() will do the right thing on x86 too ?
> 
> Yes dma_alloc_noncontiguous does all the magic. It falls back to
> alloc_dma_pages. Christoph has done a great job.

It's a really nice work yes.

Maybe the commit message could be reworded accordingly then, to
explain that we switch to dma_alloc_noncontiguous() unconditionally as
it handles the differences behind the scenes ?

> I tried it in my notebook and although the images are nothing but
> pretty it is not the APIs fault. It is because the barbers are closed
> due to the pandemic ;).

:-)

> > > With this patch on the affected architectures we can measure up to 20x
> > > performance improvement in uvc_video_copy_data_work().
> >
> > Have you measured performances on x86 to ensure there's no regression ?
> 
> Yes in the early stages. I am adding the latest x86 measurements in
> the commit message in v3 to make it more clear.
> 
> > > Eg: aarch64 with an external usb camera
> > >
> > > NON_CONTIGUOUS
> > > frames:  999
> > > packets: 999
> > > empty:   0 (0 %)
> > > errors:  0
> > > invalid: 0
> > > pts: 0 early, 0 initial, 999 ok
> > > scr: 0 count ok, 0 diff ok
> > > sof: 2048 <= sof <= 0, freq 0.000 kHz
> > > bytes 67034480 : duration 33303
> > > FPS: 29.99
> > > URB: 523446/4993 uS/qty: 104.836 avg 132.532 std 13.230 min 831.094 max (uS)
> > > header: 76564/4993 uS/qty: 15.334 avg 15.229 std 3.438 min 186.875 max (uS)
> > > latency: 468945/4992 uS/qty: 93.939 avg 132.577 std 9.531 min 824.010 max (uS)
> > > decode: 54161/4993 uS/qty: 10.847 avg 6.313 std 1.614 min 111.458 max (uS)
> > > raw decode speed: 9.931 Gbits/s
> > > raw URB handling speed: 1.025 Gbits/s
> > > throughput: 16.102 Mbits/s
> > > URB decode CPU usage 0.162600 %
> > >
> > > COHERENT
> > > frames:  999
> > > packets: 999
> > > empty:   0 (0 %)
> > > errors:  0
> > > invalid: 0
> > > pts: 0 early, 0 initial, 999 ok
> > > scr: 0 count ok, 0 diff ok
> > > sof: 2048 <= sof <= 0, freq 0.000 kHz
> > > bytes 54683536 : duration 33302
> > > FPS: 29.99
> > > URB: 1478135/4000 uS/qty: 369.533 avg 390.357 std 22.968 min 3337.865 max (uS)
> > > header: 79761/4000 uS/qty: 19.940 avg 18.495 std 1.875 min 336.719 max (uS)
> > > latency: 281077/4000 uS/qty: 70.269 avg 83.102 std 5.104 min 735.000 max (uS)
> > > decode: 1197057/4000 uS/qty: 299.264 avg 318.080 std 1.615 min 2806.667 max (uS)
> > > raw decode speed: 365.470 Mbits/s
> > > raw URB handling speed: 295.986 Mbits/s
> > > throughput: 13.136 Mbits/s
> > > URB decode CPU usage 3.594500 %
> > >
> > > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > > Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> > > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > > ---
> > >
> > > Changelog from v2: (Thanks Laurent)
> > >
> > > - Fix typos
> > > - Use the right dma direction if not capturing
> > > - Clear sgt during free
> > >
> > >  drivers/media/usb/uvc/uvc_video.c | 92 +++++++++++++++++++++++--------
> > >  drivers/media/usb/uvc/uvcvideo.h  |  5 +-
> > >  2 files changed, 74 insertions(+), 23 deletions(-)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> > > index f2f565281e63..8e60f81e2257 100644
> > > --- a/drivers/media/usb/uvc/uvc_video.c
> > > +++ b/drivers/media/usb/uvc/uvc_video.c
> > > @@ -6,11 +6,14 @@
> > >   *          Laurent Pinchart (laurent.pinchart@xxxxxxxxxxxxxxxx)
> > >   */
> > >
> > > +#include <linux/dma-mapping.h>
> > > +#include <linux/highmem.h>
> > >  #include <linux/kernel.h>
> > >  #include <linux/list.h>
> > >  #include <linux/module.h>
> > >  #include <linux/slab.h>
> > >  #include <linux/usb.h>
> > > +#include <linux/usb/hcd.h>
> > >  #include <linux/videodev2.h>
> > >  #include <linux/vmalloc.h>
> > >  #include <linux/wait.h>
> > > @@ -1096,6 +1099,34 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
> > >       return data[0];
> > >  }
> > >
> > > +static inline enum dma_data_direction stream_dir(struct uvc_streaming *stream)
> > > +{
> > > +     if (stream->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
> > > +             return DMA_FROM_DEVICE;
> > > +     else
> > > +             return DMA_TO_DEVICE;
> > > +}
> > > +
> > > +static inline struct device *stream_to_dmadev(struct uvc_streaming *stream)
> > > +{
> > > +     return bus_to_hcd(stream->dev->udev->bus)->self.sysdev;
> > > +}
> > > +
> > > +static void uvc_urb_dma_sync(struct uvc_urb *uvc_urb, bool for_device)
> >
> > Maybe nitpicking a little bit, but wouldn't the code be clearer if you
> > created uvc_urb_dma_sync_for_cpu() and uvc_urb_dma_sync_for_device() ?
> > When reading
> >
> >         uvc_urb_dma_sync(uvc_urb, true);
> >
> > I have to constantly look up the definition of the function to figure
> > out what boolean value corresponds to what direction.
> >
> > Given that uvc_urb_dma_sync(..., true) is always called right before
> > submitting the URB, we could even create a uvc_submit_urb() function
> > that groups the dma_sync_sgtable_for_device() and usb_submit_urb()
> > calls, and do without uvc_urb_dma_sync_for_device(). Up to you on this
> > one.
> 
> I Like it! thanks for the idea
> 
> >
> > With those small changes, and assuming there's no performance regression
> > on x86,
> 
> How do we take it from here. Christoph merges it from his tree?
> 
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> >
> > > +{
> > > +     struct device *dma_dev = stream_to_dmadev(uvc_urb->stream);
> > > +
> > > +     if (for_device) {
> > > +             dma_sync_sgtable_for_device(dma_dev, uvc_urb->sgt,
> > > +                                         stream_dir(uvc_urb->stream));
> > > +     } else {
> > > +             dma_sync_sgtable_for_cpu(dma_dev, uvc_urb->sgt,
> > > +                                      stream_dir(uvc_urb->stream));
> > > +             invalidate_kernel_vmap_range(uvc_urb->buffer,
> > > +                                          uvc_urb->stream->urb_size);
> > > +     }
> > > +}
> > > +
> > >  /*
> > >   * uvc_video_decode_data_work: Asynchronous memcpy processing
> > >   *
> > > @@ -1117,6 +1148,8 @@ static void uvc_video_copy_data_work(struct work_struct *work)
> > >               uvc_queue_buffer_release(op->buf);
> > >       }
> > >
> > > +     uvc_urb_dma_sync(uvc_urb, true);
> > > +
> > >       ret = usb_submit_urb(uvc_urb->urb, GFP_KERNEL);
> > >       if (ret < 0)
> > >               dev_err(&uvc_urb->stream->intf->dev,
> > > @@ -1541,10 +1574,12 @@ static void uvc_video_complete(struct urb *urb)
> > >        * Process the URB headers, and optionally queue expensive memcpy tasks
> > >        * to be deferred to a work queue.
> > >        */
> > > +     uvc_urb_dma_sync(uvc_urb, false);
> > >       stream->decode(uvc_urb, buf, buf_meta);
> > >
> > >       /* If no async work is needed, resubmit the URB immediately. */
> > >       if (!uvc_urb->async_operations) {
> > > +             uvc_urb_dma_sync(uvc_urb, true);
> > >               ret = usb_submit_urb(uvc_urb->urb, GFP_ATOMIC);
> > >               if (ret < 0)
> > >                       dev_err(&stream->intf->dev,
> > > @@ -1560,24 +1595,49 @@ static void uvc_video_complete(struct urb *urb)
> > >   */
> > >  static void uvc_free_urb_buffers(struct uvc_streaming *stream)
> > >  {
> > > +     struct device *dma_dev = stream_to_dmadev(stream);
> > >       struct uvc_urb *uvc_urb;
> > >
> > >       for_each_uvc_urb(uvc_urb, stream) {
> > >               if (!uvc_urb->buffer)
> > >                       continue;
> > >
> > > -#ifndef CONFIG_DMA_NONCOHERENT
> > > -             usb_free_coherent(stream->dev->udev, stream->urb_size,
> > > -                               uvc_urb->buffer, uvc_urb->dma);
> > > -#else
> > > -             kfree(uvc_urb->buffer);
> > > -#endif
> > > +             dma_vunmap_noncontiguous(dma_dev, uvc_urb->buffer);
> > > +             dma_free_noncontiguous(dma_dev, stream->urb_size, uvc_urb->sgt,
> > > +                                    stream_dir(stream));
> > > +
> > >               uvc_urb->buffer = NULL;
> > > +             uvc_urb->sgt = NULL;
> > >       }
> > >
> > >       stream->urb_size = 0;
> > >  }
> > >
> > > +static bool uvc_alloc_urb_buffer(struct uvc_streaming *stream,
> > > +                              struct uvc_urb *uvc_urb, gfp_t gfp_flags)
> > > +{
> > > +     struct device *dma_dev = stream_to_dmadev(stream);
> > > +
> > > +     uvc_urb->sgt = dma_alloc_noncontiguous(dma_dev, stream->urb_size,
> > > +                                            stream_dir(stream),
> > > +                                            gfp_flags, 0);
> > > +     if (!uvc_urb->sgt)
> > > +             return false;
> > > +     uvc_urb->dma = uvc_urb->sgt->sgl->dma_address;
> > > +
> > > +     uvc_urb->buffer = dma_vmap_noncontiguous(dma_dev, stream->urb_size,
> > > +                                              uvc_urb->sgt);
> > > +     if (!uvc_urb->buffer) {
> > > +             dma_free_noncontiguous(dma_dev, stream->urb_size,
> > > +                                    uvc_urb->sgt,
> > > +                                    stream_dir(stream));
> > > +             uvc_urb->sgt = NULL;
> > > +             return false;
> > > +     }
> > > +
> > > +     return true;
> > > +}
> > > +
> > >  /*
> > >   * Allocate transfer buffers. This function can be called with buffers
> > >   * already allocated when resuming from suspend, in which case it will
> > > @@ -1608,19 +1668,12 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
> > >
> > >       /* Retry allocations until one succeed. */
> > >       for (; npackets > 1; npackets /= 2) {
> > > +             stream->urb_size = psize * npackets;
> > > +
> > >               for (i = 0; i < UVC_URBS; ++i) {
> > >                       struct uvc_urb *uvc_urb = &stream->uvc_urb[i];
> > >
> > > -                     stream->urb_size = psize * npackets;
> > > -#ifndef CONFIG_DMA_NONCOHERENT
> > > -                     uvc_urb->buffer = usb_alloc_coherent(
> > > -                             stream->dev->udev, stream->urb_size,
> > > -                             gfp_flags | __GFP_NOWARN, &uvc_urb->dma);
> > > -#else
> > > -                     uvc_urb->buffer =
> > > -                         kmalloc(stream->urb_size, gfp_flags | __GFP_NOWARN);
> > > -#endif
> > > -                     if (!uvc_urb->buffer) {
> > > +                     if (!uvc_alloc_urb_buffer(stream, uvc_urb, gfp_flags)) {
> > >                               uvc_free_urb_buffers(stream);
> > >                               break;
> > >                       }
> > > @@ -1730,12 +1783,8 @@ static int uvc_init_video_isoc(struct uvc_streaming *stream,
> > >               urb->context = uvc_urb;
> > >               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 = uvc_urb->dma;
> > > -#else
> > > -             urb->transfer_flags = URB_ISO_ASAP;
> > > -#endif
> > >               urb->interval = ep->desc.bInterval;
> > >               urb->transfer_buffer = uvc_urb->buffer;
> > >               urb->complete = uvc_video_complete;
> > > @@ -1795,10 +1844,8 @@ static int uvc_init_video_bulk(struct uvc_streaming *stream,
> > >
> > >               usb_fill_bulk_urb(urb, stream->dev->udev, pipe, uvc_urb->buffer,
> > >                                 size, uvc_video_complete, uvc_urb);
> > > -#ifndef CONFIG_DMA_NONCOHERENT
> > >               urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;
> > >               urb->transfer_dma = uvc_urb->dma;
> > > -#endif
> > >
> > >               uvc_urb->urb = urb;
> > >       }
> > > @@ -1895,6 +1942,7 @@ static int uvc_video_start_transfer(struct uvc_streaming *stream,
> > >
> > >       /* Submit the URBs. */
> > >       for_each_uvc_urb(uvc_urb, stream) {
> > > +             uvc_urb_dma_sync(uvc_urb, true);
> > >               ret = usb_submit_urb(uvc_urb->urb, gfp_flags);
> > >               if (ret < 0) {
> > >                       dev_err(&stream->intf->dev,
> > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > > index 97df5ecd66c9..cce5e38133cd 100644
> > > --- a/drivers/media/usb/uvc/uvcvideo.h
> > > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > > @@ -219,6 +219,7 @@
> > >   */
> > >
> > >  struct gpio_desc;
> > > +struct sg_table;
> > >  struct uvc_device;
> > >
> > >  /* TODO: Put the most frequently accessed fields at the beginning of
> > > @@ -545,7 +546,8 @@ struct uvc_copy_op {
> > >   * @urb: the URB described by this context structure
> > >   * @stream: UVC streaming context
> > >   * @buffer: memory storage for the URB
> > > - * @dma: DMA coherent addressing for the urb_buffer
> > > + * @dma: Allocated DMA handle
> > > + * @sgt: sgt_table with the urb locations in memory
> > >   * @async_operations: counter to indicate the number of copy operations
> > >   * @copy_operations: work descriptors for asynchronous copy operations
> > >   * @work: work queue entry for asynchronous decode
> > > @@ -556,6 +558,7 @@ struct uvc_urb {
> > >
> > >       char *buffer;
> > >       dma_addr_t dma;
> > > +     struct sg_table *sgt;
> > >
> > >       unsigned int async_operations;
> > >       struct uvc_copy_op copy_operations[UVC_MAX_PACKETS];

-- 
Regards,

Laurent Pinchart