Hello,
On 7/15/2013 11:34 AM, Ricardo Ribalda Delgado wrote:
Most DMA engines have limitations regarding the number of DMA segments
(sg-buffers) that they can handle. Videobuffers can easily spread through
houndreds of pages.
In the previous aproach, the pages were allocated individually, this
could led to the creation houndreds of dma segments (sg-buffers) that
could not be handled by some DMA engines.
This patch tries to minimize the number of DMA segments by using
alloc_pages_exact. In the worst case it will behave as before, but most
of the times it will reduce the number fo dma segments
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx>
I like the idea, but the code doesn't seem to be correct. buf->pages
array is
needed for vb2_dma_sg_mmap() function to map pages to userspace. However
in your
code I don't see any place where you fill it with the pages of order higher
than 0. AFAIR vm_insert_page() can handle compound pages, but
alloc_pages_exact()
splits such pages into a set of pages of order 0, so you need to change
your code
to correctly fill buf->pages array.
---
drivers/media/v4l2-core/videobuf2-dma-sg.c | 49 +++++++++++++++++++++-------
1 file changed, 38 insertions(+), 11 deletions(-)
diff --git a/drivers/media/v4l2-core/videobuf2-dma-sg.c b/drivers/media/v4l2-core/videobuf2-dma-sg.c
index 16ae3dc..67a94ab 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-sg.c
@@ -42,10 +42,44 @@ struct vb2_dma_sg_buf {
static void vb2_dma_sg_put(void *buf_priv);
+static int vb2_dma_sg_alloc_compacted(struct vb2_dma_sg_buf *buf,
+ gfp_t gfp_flags)
+{
+ unsigned int last_page = 0;
+ void *vaddr = NULL;
+ unsigned int req_pages;
+
+ while (last_page < buf->sg_desc.num_pages) {
+ req_pages = buf->sg_desc.num_pages-last_page;
+ while (req_pages >= 1) {
+ vaddr = alloc_pages_exact(req_pages*PAGE_SIZE,
+ GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN);
+ if (vaddr)
+ break;
+ req_pages >>= 1;
+ }
+ if (!vaddr) {
+ while (--last_page >= 0)
+ __free_page(buf->pages[last_page]);
+ return -ENOMEM;
+ }
+ while (req_pages) {
+ buf->pages[last_page] = virt_to_page(vaddr);
+ sg_set_page(&buf->sg_desc.sglist[last_page],
+ buf->pages[last_page], PAGE_SIZE, 0);
+ vaddr += PAGE_SIZE;
+ last_page++;
+ req_pages--;
+ }
+ }
+
+ return 0;
+}
+
static void *vb2_dma_sg_alloc(void *alloc_ctx, unsigned long size, gfp_t gfp_flags)
{
struct vb2_dma_sg_buf *buf;
- int i;
+ int ret;
buf = kzalloc(sizeof *buf, GFP_KERNEL);
if (!buf)
@@ -69,14 +103,9 @@ static void *vb2_dma_sg_alloc(void *alloc_ctx, unsigned long size, gfp_t gfp_fla
if (!buf->pages)
goto fail_pages_array_alloc;
- for (i = 0; i < buf->sg_desc.num_pages; ++i) {
- buf->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO |
- __GFP_NOWARN | gfp_flags);
- if (NULL == buf->pages[i])
- goto fail_pages_alloc;
- sg_set_page(&buf->sg_desc.sglist[i],
- buf->pages[i], PAGE_SIZE, 0);
- }
+ ret = vb2_dma_sg_alloc_compacted(buf, gfp_flags);
+ if (ret)
+ goto fail_pages_alloc;
buf->handler.refcount = &buf->refcount;
buf->handler.put = vb2_dma_sg_put;
@@ -89,8 +118,6 @@ static void *vb2_dma_sg_alloc(void *alloc_ctx, unsigned long size, gfp_t gfp_fla
return buf;
fail_pages_alloc:
- while (--i >= 0)
- __free_page(buf->pages[i]);
kfree(buf->pages);
fail_pages_array_alloc:
Best regards
--
Marek Szyprowski
Samsung R&D Institute Poland
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