Re: [PATCH 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API
From: Ricardo Ribalda
Date: Tue Nov 24 2020 - 12:26:08 EST
Hi Robin
On Tue, Nov 24, 2020 at 5:29 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> On 2020-11-24 15:38, Ricardo Ribalda wrote:
> > On architectures where the is no coherent caching such as ARM use the
> > dma_alloc_noncontiguos API and handle manually the cache flushing using
> > dma_sync_single().
> >
> > With this patch on the affected architectures we can measure up to 20x
> > performance improvement in uvc_video_copy_data_work().
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > ---
> > drivers/media/usb/uvc/uvc_video.c | 74 ++++++++++++++++++++++++++-----
> > drivers/media/usb/uvc/uvcvideo.h | 1 +
> > 2 files changed, 63 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> > index a6a441d92b94..9e90b261428a 100644
> > --- a/drivers/media/usb/uvc/uvc_video.c
> > +++ b/drivers/media/usb/uvc/uvc_video.c
> > @@ -1490,6 +1490,11 @@ static void uvc_video_encode_bulk(struct uvc_urb *uvc_urb,
> > urb->transfer_buffer_length = stream->urb_size - len;
> > }
> >
> > +static inline struct device *stream_to_dmadev(struct uvc_streaming *stream)
> > +{
> > + return stream->dev->udev->bus->controller->parent;
> > +}
> > +
> > static void uvc_video_complete(struct urb *urb)
> > {
> > struct uvc_urb *uvc_urb = urb->context;
> > @@ -1539,6 +1544,11 @@ 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.
> > */
> > + if (uvc_urb->pages)
> > + dma_sync_single_for_cpu(stream_to_dmadev(stream),
> > + urb->transfer_dma,
> > + urb->transfer_buffer_length,
> > + DMA_FROM_DEVICE);
>
> This doesn't work. Even in iommu-dma, the streaming API still expects to
> work on physically-contiguous memory that could have been passed to
> dma_map_single() in the first place. As-is, this will invalidate
> transfer_buffer_length bytes from the start of the *first* physical
> page, and thus destroy random other data if lines from subsequent
> unrelated pages are dirty in caches.
>
> The only feasible way to do a DMA sync on disjoint pages in a single
> call is with a scatterlist.
Thanks for pointing this out. I guess I was lucky on my hardware and
the areas were always contiguous.
Will rework and send back to the list.
Thanks again.
>
> Robin.
>
> > stream->decode(uvc_urb, buf, buf_meta);
> >
> > /* If no async work is needed, resubmit the URB immediately. */
> > @@ -1566,8 +1576,15 @@ static void uvc_free_urb_buffers(struct uvc_streaming *stream)
> > continue;
> >
> > #ifndef CONFIG_DMA_NONCOHERENT
> > - usb_free_coherent(stream->dev->udev, stream->urb_size,
> > - uvc_urb->buffer, uvc_urb->dma);
> > + if (uvc_urb->pages) {
> > + vunmap(uvc_urb->buffer);
> > + dma_free_noncontiguous(stream_to_dmadev(stream),
> > + stream->urb_size,
> > + uvc_urb->pages, uvc_urb->dma);
> > + } else {
> > + usb_free_coherent(stream->dev->udev, stream->urb_size,
> > + uvc_urb->buffer, uvc_urb->dma);
> > + }
> > #else
> > kfree(uvc_urb->buffer);
> > #endif
> > @@ -1577,6 +1594,47 @@ static void uvc_free_urb_buffers(struct uvc_streaming *stream)
> > stream->urb_size = 0;
> > }
> >
> > +#ifndef CONFIG_DMA_NONCOHERENT
> > +static bool uvc_alloc_urb_buffer(struct uvc_streaming *stream,
> > + struct uvc_urb *uvc_urb, gfp_t gfp_flags)
> > +{
> > + struct device *dma_dev = dma_dev = stream_to_dmadev(stream);
> > +
> > + if (!dma_can_alloc_noncontiguous(dma_dev)) {
> > + uvc_urb->buffer = usb_alloc_coherent(stream->dev->udev,
> > + stream->urb_size,
> > + gfp_flags | __GFP_NOWARN,
> > + &uvc_urb->dma);
> > + return uvc_urb->buffer != NULL;
> > + }
> > +
> > + uvc_urb->pages = dma_alloc_noncontiguous(dma_dev, stream->urb_size,
> > + &uvc_urb->dma,
> > + gfp_flags | __GFP_NOWARN, 0);
> > + if (!uvc_urb->pages)
> > + return false;
> > +
> > + uvc_urb->buffer = vmap(uvc_urb->pages,
> > + PAGE_ALIGN(stream->urb_size) >> PAGE_SHIFT,
> > + VM_DMA_COHERENT, PAGE_KERNEL);
> > + if (!uvc_urb->buffer) {
> > + dma_free_noncontiguous(dma_dev, stream->urb_size,
> > + uvc_urb->pages, uvc_urb->dma);
> > + return false;
> > + }
> > +
> > + return true;
> > +}
> > +#else
> > +static bool uvc_alloc_urb_buffer(struct uvc_streaming *stream,
> > + struct uvc_urb *uvc_urb, gfp_t gfp_flags)
> > +{
> > + uvc_urb->buffer = kmalloc(stream->urb_size, gfp_flags | __GFP_NOWARN);
> > +
> > + return uvc_urb->buffer != NULL;
> > +}
> > +#endif
> > +
> > /*
> > * Allocate transfer buffers. This function can be called with buffers
> > * already allocated when resuming from suspend, in which case it will
> > @@ -1607,19 +1665,11 @@ 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;
> > }
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index a3dfacf069c4..3e3ef1f1daa5 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -532,6 +532,7 @@ struct uvc_urb {
> >
> > char *buffer;
> > dma_addr_t dma;
> > + struct page **pages;
> >
> > unsigned int async_operations;
> > struct uvc_copy_op copy_operations[UVC_MAX_PACKETS];
> >
--
Ricardo Ribalda