Messages in this thread | | | Subject | Re: [PATCH 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API | From | Robin Murphy <> | Date | Tue, 24 Nov 2020 16:29:20 +0000 |
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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@chromium.org> > --- > 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.
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]; >
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