# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1206955945 -3600
# Node ID 5486a234923da1fbab13eef6165f25c54ab63bd9
# Parent 171ffa6bf3a51ddf83d559c4d9312a3603497ff1
Xen dma: avoid unnecessarily SWIOTLB bounce buffering.
On Xen kernels, BIOVEC_PHYS_MERGEABLE permits merging of disk IOs that
span multiple pages, provided that the pages are both
pseudophysically- AND machine-contiguous ---
(((bvec_to_phys((vec1)) + (vec1)->bv_len) ==
bvec_to_phys((vec2))) && \
((bvec_to_pseudophys((vec1)) + (vec1)->bv_len) == \
bvec_to_pseudophys((vec2))))
However, this best-effort merging of adjacent pages can occur in
regions of dom0 memory which just happen, by virtue of having been
initially set up that way, to be machine-contiguous. Such pages
which occur outside of a range created by xen_create_contiguous_
region won't be seen as contiguous by range_straddles_page_boundary(),
so the pci-dma-xen.c code for dma_map_sg() will send these regions
to the swiotlb for bounce buffering.
This patch adds a new check, check_pages_physically_contiguous(),
to the test for pages stradding page boundaries both in
swiotlb_map_sg() and dma_map_sg(), to capture these ranges and map
them directly via virt_to_bus() mapping rather than through the
swiotlb.
Signed-off-by: Stephen Tweedie <sct@xxxxxxxxxx>
---
arch/i386/kernel/pci-dma-xen.c | 33 ++++++++++++++++++++++++++++
include/asm-i386/mach-xen/asm/dma-mapping.h | 8 ------
2 files changed, 34 insertions(+), 7 deletions(-)
diff -r 171ffa6bf3a5 -r 5486a234923d arch/i386/kernel/pci-dma-xen.c
--- a/arch/i386/kernel/pci-dma-xen.c Fri Mar 28 14:27:38 2008 +0000
+++ b/arch/i386/kernel/pci-dma-xen.c Mon Mar 31 10:32:25 2008 +0100
@@ -76,6 +76,39 @@ do { \
BUG(); \
} \
} while (0)
+
+static int check_pages_physically_contiguous(unsigned long pfn,
+ unsigned int offset,
+ size_t length)
+{
+ unsigned long next_mfn;
+ int i;
+ int nr_pages;
+
+ next_mfn = pfn_to_mfn(pfn);
+ nr_pages = (offset + length + PAGE_SIZE-1) >> PAGE_SHIFT;
+
+ for (i = 1; i < nr_pages; i++) {
+ if (pfn_to_mfn(++pfn) != ++next_mfn)
+ return 0;
+ }
+ return 1;
+}
+
+int range_straddles_page_boundary(paddr_t p, size_t size)
+{
+ extern unsigned long *contiguous_bitmap;
+ unsigned long pfn = p >> PAGE_SHIFT;
+ unsigned int offset = p & ~PAGE_MASK;
+
+ if (offset + size <= PAGE_SIZE)
+ return 0;
+ if (test_bit(pfn, contiguous_bitmap))
+ return 0;
+ if (check_pages_physically_contiguous(pfn, offset, size))
+ return 0;
+ return 1;
+}
int
dma_map_sg(struct device *hwdev, struct scatterlist *sg, int nents,
diff -r 171ffa6bf3a5 -r 5486a234923d include/asm-i386/mach-xen/asm/dma-mapping.h
--- a/include/asm-i386/mach-xen/asm/dma-mapping.h Fri Mar 28 14:27:38
2008 +0000
+++ b/include/asm-i386/mach-xen/asm/dma-mapping.h Mon Mar 31 10:32:25
2008 +0100
@@ -22,13 +22,7 @@ address_needs_mapping(struct device *hwd
return (addr & ~mask) != 0;
}
-static inline int
-range_straddles_page_boundary(paddr_t p, size_t size)
-{
- extern unsigned long *contiguous_bitmap;
- return ((((p & ~PAGE_MASK) + size) > PAGE_SIZE) &&
- !test_bit(p >> PAGE_SHIFT, contiguous_bitmap));
-}
+extern int range_straddles_page_boundary(paddr_t p, size_t size);
#define dma_alloc_noncoherent(d, s, h, f) dma_alloc_coherent(d, s, h, f)
#define dma_free_noncoherent(d, s, v, h) dma_free_coherent(d, s, v, h)
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