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 <riba...@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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