Jens Axboe wrote:
<snip>
> @@ -323,13 +324,17 @@ static int __dma_map_cont(struct scatterlist *sg, int start, int stopat,
> {
> unsigned long iommu_start = alloc_iommu(pages);
> unsigned long iommu_page = iommu_start;
> - int i;
> + struct scatterlist *s;
> + int i, nelems;
>
> if (iommu_start == -1)
> return -1;
> +
> + nelems = stopat - start;
> + while (start--)
> + sg = sg_next(sg);
Ouch. This will suck if we merge many times in a long list.
How about keeping and passing start as a struct scatterlist * rather
than an index? (see attached example, (compiles, bu untested though)
>
> - for (i = start; i < stopat; i++) {
> - struct scatterlist *s = &sg[i];
> + for_each_sg(sg, s, nelems, i) {
> unsigned long pages, addr;
> unsigned long phys_addr = s->dma_address;
There seems to be a bug hiding here as now i is in [0, nelems) now,
not [start, stopat) so "if (i == start)" below should turn into "if (i == 0)"
this is fixed by comparing pointers instead way in the attached example.
>
> @@ -360,12 +365,14 @@ static inline int dma_map_cont(struct scatterlist *sg, int start, int stopat,
> struct scatterlist *sout,
> unsigned long pages, int need)
> {
> - if (!need) {
> + if (!need) {
> BUG_ON(stopat - start != 1);
> - *sout = sg[start];
> - sout->dma_length = sg[start].length;
> + while (--start)
> + sg = sg_next(sg);
same efficiency issue as above.
> + *sout = *sg;
> + sout->dma_length = sg->length;
> return 0;
> - }
> + }
> return __dma_map_cont(sg, start, stopat, sout, pages);
> }
>
<snip>
diff --git a/arch/x86_64/kernel/pci-gart.c b/arch/x86_64/kernel/pci-gart.c
index 8bc2ed7..48ce635 100644
--- a/arch/x86_64/kernel/pci-gart.c
+++ b/arch/x86_64/kernel/pci-gart.c
@@ -319,27 +319,23 @@ static int dma_map_sg_nonforce(struct device *dev, struct scatterlist *sg,
}
/* Map multiple scatterlist entries continuous into the first. */
-static int __dma_map_cont(struct scatterlist *sg, int start, int stopat,
+static int __dma_map_cont(struct scatterlist *start, int nelems,
struct scatterlist *sout, unsigned long pages)
{
unsigned long iommu_start = alloc_iommu(pages);
unsigned long iommu_page = iommu_start;
struct scatterlist *s;
- int i, nelems;
+ int i;
if (iommu_start == -1)
return -1;
- nelems = stopat - start;
- while (start--)
- sg = sg_next(sg);
-
- for_each_sg(sg, s, nelems, i) {
+ for_each_sg(start, s, nelems, i) {
unsigned long pages, addr;
unsigned long phys_addr = s->dma_address;
- BUG_ON(i > start && s->offset);
- if (i == start) {
+ BUG_ON(s != start && s->offset);
+ if (s == start) {
*sout = *s;
sout->dma_address = iommu_bus_base;
sout->dma_address += iommu_page*PAGE_SIZE + s->offset;
@@ -361,19 +357,17 @@ static int __dma_map_cont(struct scatterlist *sg, int start, int stopat,
return 0;
}
-static inline int dma_map_cont(struct scatterlist *sg, int start, int stopat,
+static inline int dma_map_cont(struct scatterlist *start, int nelems,
struct scatterlist *sout,
unsigned long pages, int need)
{
if (!need) {
- BUG_ON(stopat - start != 1);
- while (--start)
- sg = sg_next(sg);
- *sout = *sg;
- sout->dma_length = sg->length;
+ BUG_ON(nelems != 1);
+ *sout = *start;
+ sout->dma_length = start->length;
return 0;
}
- return __dma_map_cont(sg, start, stopat, sout, pages);
+ return __dma_map_cont(start, nelems, sout, pages);
}
/*
@@ -387,7 +381,7 @@ int gart_map_sg(struct device *dev, struct scatterlist *sg, int nents, int dir)
int start;
unsigned long pages = 0;
int need = 0, nextneed;
- struct scatterlist *s, *ps;
+ struct scatterlist *s, *ps, *start_sg;
if (nents == 0)
return 0;
@@ -397,6 +391,7 @@ int gart_map_sg(struct device *dev, struct scatterlist *sg, int nents, int dir)
out = 0;
start = 0;
+ start_sg = sg;
ps = NULL; /* shut up gcc */
for_each_sg(sg, s, nents, i) {
dma_addr_t addr = page_to_phys(s->page) + s->offset;
@@ -411,12 +406,13 @@ int gart_map_sg(struct device *dev, struct scatterlist *sg, int nents, int dir)
boundary and the new one doesn't have an offset. */
if (!iommu_merge || !nextneed || !need || s->offset ||
(ps->offset + ps->length) % PAGE_SIZE) {
- if (dma_map_cont(sg, start, i, sg+out, pages,
- need) < 0)
+ if (dma_map_cont(start_sg, i - start, sg+out,
+ pages, need) < 0)
goto error;
out++;
pages = 0;
- start = i;
+ start = i;
+ start_sg = s;
}
}
@@ -424,7 +420,7 @@ int gart_map_sg(struct device *dev, struct scatterlist *sg, int nents, int dir)
pages += to_pages(s->offset, s->length);
ps = s;
}
- if (dma_map_cont(sg, start, i, sg+out, pages, need) < 0)
+ if (dma_map_cont(start_sg, i - start, sg+out, pages, need) < 0)
goto error;
out++;
flush_gart();
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