[PATCH v4 6/6] media: uvcvideo: Use dma_alloc_noncontiguous API

From: Ricardo Ribalda
Date: Fri Mar 12 2021 - 18:56:25 EST

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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().

If the architechture has coherent cache, the API falls back to
alloc_dma_pages, so we can remove the coherent caching code-path from the
driver, making it simpler.

With this patch on the affected architectures we can measure up to 20x
performance improvement in uvc_video_copy_data_work().

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 %

In non-affected architectures we see no significant impact.

Eg: x86 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 70179056 : duration 33301
FPS: 29.99
URB: 288901/4897 uS/qty: 58.995 avg 26.022 std 4.319 min 253.853 max (uS)
header: 54792/4897 uS/qty: 11.189 avg 6.218 std 0.620 min 61.750 max (uS)
latency: 236602/4897 uS/qty: 48.315 avg 24.244 std 1.764 min 240.924 max (uS)
decode: 52298/4897 uS/qty: 10.679 avg 8.299 std 1.638 min 108.861 max (uS)
raw decode speed: 10.796 Gbits/s
raw URB handling speed: 1.949 Gbits/s
throughput: 16.859 Mbits/s
URB decode CPU usage 0.157000 %

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 71818320 : duration 33301
FPS: 29.99
URB: 321021/5000 uS/qty: 64.204 avg 23.001 std 10.430 min 268.837 max (uS)
header: 54308/5000 uS/qty: 10.861 avg 5.104 std 0.778 min 54.736 max (uS)
latency: 268799/5000 uS/qty: 53.759 avg 21.827 std 6.095 min 255.153 max (uS)
decode: 52222/5000 uS/qty: 10.444 avg 7.137 std 1.874 min 71.103 max (uS)
raw decode speed: 11.048 Gbits/s
raw URB handling speed: 1.789 Gbits/s
throughput: 17.253 Mbits/s
URB decode CPU usage 0.156800 %

Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---

Changelog from v3 (Thanks Laurent!):

- Rename stream_dir and stream_to_dmadev to avoid collisions
- Improve commit message

drivers/media/usb/uvc/uvc_video.c | 94 +++++++++++++++++++++++--------
drivers/media/usb/uvc/uvcvideo.h | 5 +-
2 files changed, 73 insertions(+), 26 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index f2f565281e63..cdd8eb500bb7 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 +1099,29 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
return data[0];
}

+static inline enum dma_data_direction uvc_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 *uvc_stream_to_dmadev(struct uvc_streaming *stream)
+{
+ return bus_to_hcd(stream->dev->udev->bus)->self.sysdev;
+}
+
+static int uvc_submit_urb(struct uvc_urb *uvc_urb, gfp_t mem_flags)
+{
+ /* Sync DMA. */
+ dma_sync_sgtable_for_device(uvc_stream_to_dmadev(uvc_urb->stream),
+ uvc_urb->sgt,
+ uvc_stream_dir(uvc_urb->stream));
+ return usb_submit_urb(uvc_urb->urb, GFP_KERNEL);
+}
+
/*
* uvc_video_decode_data_work: Asynchronous memcpy processing
*
@@ -1117,7 +1143,7 @@ static void uvc_video_copy_data_work(struct work_struct *work)
uvc_queue_buffer_release(op->buf);
}

- ret = usb_submit_urb(uvc_urb->urb, GFP_KERNEL);
+ ret = uvc_submit_urb(uvc_urb, GFP_KERNEL);
if (ret < 0)
dev_err(&uvc_urb->stream->intf->dev,
"Failed to resubmit video URB (%d).\n", ret);
@@ -1537,6 +1563,12 @@ static void uvc_video_complete(struct urb *urb)
/* Re-initialise the URB async work. */
uvc_urb->async_operations = 0;

+ /* Sync DMA and invalidate vmap range. */
+ dma_sync_sgtable_for_cpu(uvc_stream_to_dmadev(uvc_urb->stream),
+ uvc_urb->sgt, uvc_stream_dir(stream));
+ invalidate_kernel_vmap_range(uvc_urb->buffer,
+ uvc_urb->stream->urb_size);
+
/*
* Process the URB headers, and optionally queue expensive memcpy tasks
* to be deferred to a work queue.
@@ -1545,7 +1577,7 @@ static void uvc_video_complete(struct urb *urb)

/* If no async work is needed, resubmit the URB immediately. */
if (!uvc_urb->async_operations) {
- ret = usb_submit_urb(uvc_urb->urb, GFP_ATOMIC);
+ ret = uvc_submit_urb(uvc_urb, GFP_ATOMIC);
if (ret < 0)
dev_err(&stream->intf->dev,
"Failed to resubmit video URB (%d).\n", ret);
@@ -1560,24 +1592,49 @@ static void uvc_video_complete(struct urb *urb)
*/
static void uvc_free_urb_buffers(struct uvc_streaming *stream)
{
+ struct device *dma_dev = uvc_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,
+ uvc_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 = uvc_stream_to_dmadev(stream);
+
+ uvc_urb->sgt = dma_alloc_noncontiguous(dma_dev, stream->urb_size,
+ uvc_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,
+ uvc_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 +1665,12 @@ 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 +1780,8 @@ 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 +1841,8 @@ 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;
}
@@ -1895,7 +1939,7 @@ static int uvc_video_start_transfer(struct uvc_streaming *stream,

/* Submit the URBs. */
for_each_uvc_urb(uvc_urb, stream) {
- ret = usb_submit_urb(uvc_urb->urb, gfp_flags);
+ ret = uvc_submit_urb(uvc_urb, gfp_flags);
if (ret < 0) {
dev_err(&stream->intf->dev,
"Failed to submit URB %u (%d).\n",
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];
--
2.31.0.rc2.261.g7f71774620-goog

Next message: Daeho Jeong: "Re: [PATCH v4] f2fs: add sysfs nodes to get runtime compression stat"
Previous message: Dimitri John Ledkov: "Re: [PATCH 4/4] integrity: Load mokx variables into the blacklist keyring"
Next in thread: Ricardo Ribalda: "Re: [PATCH v4 6/6] media: uvcvideo: Use dma_alloc_noncontiguous API"
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