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busdma: better handling of small segment bouncing

Browse source 
Typically, when a DMA transaction requires bouncing, we will break up
the request into segments that are, at maximum, page-sized.

However, in the atypical case of a driver whose maximum segment size is
smaller than PAGE_SIZE, we end up inefficiently assigning each segment
its own bounce page. For example, the dwmmc driver has a maximum segment
size of 2048 (PAGE_SIZE / 2); a 4-page transfer ends up requiring 8
bounce pages in the current scheme.

We should attempt to batch segments into bounce pages more efficiently.
This is achieved by pushing all considerations of the maximum segment
size into the new _bus_dmamap_addsegs() function, which wraps
_bus_dmamap_addseg(). Thus we allocate the minimal number of bounce
pages required to complete the entire transfer, while still performing
the transfer with smaller-sized transactions.

For most drivers with a segment size >= PAGE_SIZE, this will have no
impact. For drivers like dwmmc mentioned above, this improves the memory
and performance efficiency when bouncing a large transfer.

Co-authored-by:	jhb
Reviewed by:	jhb
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D45048
This commit is contained in:
Mitchell Horne 2024-02-14 12:56:13 -04:00
parent 5604069824
commit a77e1f0f81
6 changed files with 75 additions and 91 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

21
sys/arm/arm/busdma_machdep.c
View file

@ -796,7 +796,7 @@ _bus_dmamap_count_phys(bus_dma_tag_t dmat, bus_dmamap_t map, vm_paddr_t buf,
*/
curaddr = buf;
while (buflen != 0) {
sgsize = MIN(buflen, dmat->maxsegsz);
sgsize = buflen;
if (must_bounce(dmat, map, curaddr, sgsize) != 0) {
sgsize = MIN(sgsize,
PAGE_SIZE - (curaddr & PAGE_MASK));
@ -833,7 +833,6 @@ _bus_dmamap_count_pages(bus_dma_tag_t dmat, pmap_t pmap, bus_dmamap_t map,
while (vaddr < vendaddr) {
sg_len = MIN(vendaddr - vaddr,
(PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK)));
sg_len = MIN(sg_len, dmat->maxsegsz);
if (__predict_true(pmap == kernel_pmap))
paddr = pmap_kextract(vaddr);
else
@ -884,7 +883,7 @@ _bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map, vm_paddr_t buf,
while (buflen > 0) {
curaddr = buf;
sgsize = MIN(buflen, dmat->maxsegsz);
sgsize = buflen;
if (map->pagesneeded != 0 && must_bounce(dmat, map, curaddr,
sgsize)) {
sgsize = MIN(sgsize, PAGE_SIZE - (curaddr & PAGE_MASK));
@ -908,9 +907,8 @@ _bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map, vm_paddr_t buf,
} else
sl->datacount += sgsize;
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
buf += sgsize;
buflen -= sgsize;
@ -1000,11 +998,7 @@ _bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
/*
* Compute the segment size, and adjust counts.
*/
sgsize = PAGE_SIZE - (curaddr & PAGE_MASK);
if (sgsize > dmat->maxsegsz)
sgsize = dmat->maxsegsz;
if (buflen < sgsize)
sgsize = buflen;
sgsize = MIN(buflen, PAGE_SIZE - (curaddr & PAGE_MASK));
if (map->pagesneeded != 0 && must_bounce(dmat, map, curaddr,
sgsize)) {
@ -1037,9 +1031,8 @@ _bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
} else
sl->datacount += sgsize;
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
vaddr += sgsize;
buflen -= sgsize;

24
sys/arm64/arm64/busdma_bounce.c
View file

@ -643,7 +643,7 @@ _bus_dmamap_pagesneeded(bus_dma_tag_t dmat, bus_dmamap_t map, vm_paddr_t buf,
count = 0;
curaddr = buf;
while (buflen != 0) {
sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = buflen;
if (must_bounce(dmat, map, curaddr, sgsize)) {
sgsize = MIN(sgsize,
PAGE_SIZE - (curaddr & PAGE_MASK));
@ -696,15 +696,13 @@ _bus_dmamap_count_pages(bus_dma_tag_t dmat, bus_dmamap_t map, pmap_t pmap,
vendaddr = (vm_offset_t)buf + buflen;
while (vaddr < vendaddr) {
sg_len = PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK);
sg_len = MIN(sg_len, dmat->common.maxsegsz);
sg_len = MIN(vendaddr - vaddr,
PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK));
if (pmap == kernel_pmap)
paddr = pmap_kextract(vaddr);
else
paddr = pmap_extract(pmap, vaddr);
if (must_bounce(dmat, map, paddr,
min(vendaddr - vaddr, (PAGE_SIZE - ((vm_offset_t)vaddr &
PAGE_MASK)))) != 0) {
if (must_bounce(dmat, map, paddr, sg_len) != 0) {
sg_len = roundup2(sg_len,
dmat->common.alignment);
map->pagesneeded++;
@ -746,7 +744,7 @@ bounce_bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map,
while (buflen > 0) {
curaddr = buf;
sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = buflen;
if (map->pagesneeded != 0 &&
must_bounce(dmat, map, curaddr, sgsize)) {
/*
@ -780,9 +778,8 @@ bounce_bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map,
} else
sl->datacount += sgsize;
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
buf += sgsize;
buflen -= sgsize;
@ -858,7 +855,7 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
/*
* Compute the segment size, and adjust counts.
*/
sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = buflen;
if ((map->flags & DMAMAP_FROM_DMAMEM) == 0)
sgsize = MIN(sgsize, PAGE_SIZE - (curaddr & PAGE_MASK));
@ -897,9 +894,8 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
} else
sl->datacount += sgsize;
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
vaddr += sgsize;
buflen -= sgsize;

22
sys/kern/subr_busdma_bounce.c
View file

@ -499,6 +499,28 @@ _bus_dmamap_addseg(bus_dma_tag_t dmat, bus_dmamap_t map, bus_addr_t curaddr,
return (sgsize);
}
/*
* Add a contiguous physical range to the segment list, respecting the tag's
* maximum segment size and splitting it into multiple segments as necessary.
*/
static bool
_bus_dmamap_addsegs(bus_dma_tag_t dmat, bus_dmamap_t map, bus_addr_t curaddr,
bus_size_t sgsize, bus_dma_segment_t *segs, int *segp)
{
bus_size_t done, todo;
while (sgsize > 0) {
todo = MIN(sgsize, dmat_maxsegsz(dmat));
done = _bus_dmamap_addseg(dmat, map, curaddr, todo, segs,
segp);
if (done == 0)
return (false);
curaddr += done;
sgsize -= done;
}
return (true);
}
static void
busdma_thread(void *dummy __unused)
{

26
sys/powerpc/powerpc/busdma_machdep.c
View file

@ -487,7 +487,7 @@ _bus_dmamap_count_phys(bus_dma_tag_t dmat, bus_dmamap_t map, vm_paddr_t buf,
*/
curaddr = buf;
while (buflen != 0) {
sgsize = MIN(buflen, dmat->maxsegsz);
sgsize = buflen;
if (must_bounce(dmat, curaddr)) {
sgsize = MIN(sgsize,
PAGE_SIZE - (curaddr & PAGE_MASK));
@ -523,8 +523,8 @@ _bus_dmamap_count_pages(bus_dma_tag_t dmat, bus_dmamap_t map, pmap_t pmap,
while (vaddr < vendaddr) {
bus_size_t sg_len;
sg_len = PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK);
sg_len = MIN(sg_len, dmat->maxsegsz);
sg_len = MIN(vendaddr - vaddr,
PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK));
if (pmap == kernel_pmap)
paddr = pmap_kextract(vaddr);
else
@ -569,15 +569,14 @@ _bus_dmamap_load_phys(bus_dma_tag_t dmat,
while (buflen > 0) {
curaddr = buf;
sgsize = MIN(buflen, dmat->maxsegsz);
sgsize = buflen;
if (map->pagesneeded != 0 && must_bounce(dmat, curaddr)) {
sgsize = MIN(sgsize, PAGE_SIZE - (curaddr & PAGE_MASK));
curaddr = add_bounce_page(dmat, map, 0, curaddr,
sgsize);
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
buf += sgsize;
buflen -= sgsize;
@ -632,8 +631,6 @@ _bus_dmamap_load_buffer(bus_dma_tag_t dmat,
vaddr = (vm_offset_t)buf;
while (buflen > 0) {
bus_size_t max_sgsize;
/*
* Get the physical address for this segment.
*/
@ -648,20 +645,15 @@ _bus_dmamap_load_buffer(bus_dma_tag_t dmat,
/*
* Compute the segment size, and adjust counts.
*/
max_sgsize = MIN(buflen, dmat->maxsegsz);
sgsize = PAGE_SIZE - (curaddr & PAGE_MASK);
sgsize = MIN(buflen, PAGE_SIZE - (curaddr & PAGE_MASK));
if (map->pagesneeded != 0 && must_bounce(dmat, curaddr)) {
sgsize = roundup2(sgsize, dmat->alignment);
sgsize = MIN(sgsize, max_sgsize);
curaddr = add_bounce_page(dmat, map, kvaddr, curaddr,
sgsize);
} else {
sgsize = MIN(sgsize, max_sgsize);
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
vaddr += sgsize;
buflen -= sgsize;

27
sys/riscv/riscv/busdma_bounce.c
View file

@ -497,7 +497,7 @@ _bus_dmamap_count_phys(bus_dma_tag_t dmat, bus_dmamap_t map, vm_paddr_t buf,
*/
curaddr = buf;
while (buflen != 0) {
sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = buflen;
if (addr_needs_bounce(dmat, curaddr)) {
sgsize = MIN(sgsize,
PAGE_SIZE - (curaddr & PAGE_MASK));
@ -534,8 +534,8 @@ _bus_dmamap_count_pages(bus_dma_tag_t dmat, bus_dmamap_t map, pmap_t pmap,
vendaddr = (vm_offset_t)buf + buflen;
while (vaddr < vendaddr) {
sg_len = PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK);
sg_len = MIN(sg_len, dmat->common.maxsegsz);
sg_len = MIN(vendaddr - vaddr,
PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK));
if (pmap == kernel_pmap)
paddr = pmap_kextract(vaddr);
else
@ -582,7 +582,7 @@ bounce_bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map,
while (buflen > 0) {
curaddr = buf;
sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = buflen;
if (((dmat->bounce_flags & BF_COULD_BOUNCE) != 0) &&
map->pagesneeded != 0 &&
addr_needs_bounce(dmat, curaddr)) {
@ -607,9 +607,8 @@ bounce_bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map,
} else
sl->datacount += sgsize;
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
buf += sgsize;
buflen -= sgsize;
@ -631,7 +630,7 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
int *segp)
{
struct sync_list *sl;
bus_size_t sgsize, max_sgsize;
bus_size_t sgsize;
bus_addr_t curaddr, sl_pend;
vm_offset_t kvaddr, vaddr, sl_vend;
int error;
@ -668,17 +667,14 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
/*
* Compute the segment size, and adjust counts.
*/
max_sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = PAGE_SIZE - (curaddr & PAGE_MASK);
sgsize = MIN(buflen, PAGE_SIZE - (curaddr & PAGE_MASK));
if (((dmat->bounce_flags & BF_COULD_BOUNCE) != 0) &&
map->pagesneeded != 0 &&
addr_needs_bounce(dmat, curaddr)) {
sgsize = roundup2(sgsize, dmat->common.alignment);
sgsize = MIN(sgsize, max_sgsize);
curaddr = add_bounce_page(dmat, map, kvaddr, curaddr,
sgsize);
} else if ((dmat->bounce_flags & BF_COHERENT) == 0) {
sgsize = MIN(sgsize, max_sgsize);
if (map->sync_count > 0) {
sl_pend = sl->paddr + sl->datacount;
sl_vend = sl->vaddr + sl->datacount;
@ -704,12 +700,9 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
sl->datacount = sgsize;
} else
sl->datacount += sgsize;
} else {
sgsize = MIN(sgsize, max_sgsize);
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
vaddr += sgsize;
buflen -= sgsize;

46
sys/x86/x86/busdma_bounce.c
View file

@ -511,7 +511,7 @@ _bus_dmamap_pagesneeded(bus_dma_tag_t dmat, vm_paddr_t buf, bus_size_t buflen,
count = 0;
curaddr = buf;
while (buflen != 0) {
sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = buflen;
if (must_bounce(dmat, curaddr)) {
sgsize = MIN(sgsize,
PAGE_SIZE - (curaddr & PAGE_MASK));
@ -563,8 +563,8 @@ _bus_dmamap_count_pages(bus_dma_tag_t dmat, bus_dmamap_t map, pmap_t pmap,
vendaddr = (vm_offset_t)buf + buflen;
while (vaddr < vendaddr) {
sg_len = PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK);
sg_len = MIN(sg_len, dmat->common.maxsegsz);
sg_len = MIN(vendaddr - vaddr,
PAGE_SIZE - ((vm_offset_t)vaddr & PAGE_MASK));
if (pmap == kernel_pmap)
paddr = pmap_kextract(vaddr);
else
@ -584,7 +584,7 @@ static void
_bus_dmamap_count_ma(bus_dma_tag_t dmat, bus_dmamap_t map, struct vm_page **ma,
int ma_offs, bus_size_t buflen, int flags)
{
bus_size_t sg_len, max_sgsize;
bus_size_t sg_len;
int page_index;
vm_paddr_t paddr;
@ -604,12 +604,10 @@ _bus_dmamap_count_ma(bus_dma_tag_t dmat, bus_dmamap_t map, struct vm_page **ma,
while (buflen > 0) {
paddr = VM_PAGE_TO_PHYS(ma[page_index]) + ma_offs;
sg_len = PAGE_SIZE - ma_offs;
max_sgsize = MIN(buflen, dmat->common.maxsegsz);
sg_len = MIN(sg_len, max_sgsize);
sg_len = MIN(sg_len, buflen);
if (must_bounce(dmat, paddr)) {
sg_len = roundup2(sg_len,
dmat->common.alignment);
sg_len = MIN(sg_len, max_sgsize);
KASSERT(vm_addr_align_ok(sg_len,
dmat->common.alignment),
("Segment size is not aligned"));
@ -656,7 +654,7 @@ bounce_bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map,
while (buflen > 0) {
curaddr = buf;
sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = buflen;
if ((dmat->bounce_flags & BUS_DMA_COULD_BOUNCE) != 0 &&
map->pagesneeded != 0 &&
must_bounce(dmat, curaddr)) {
@ -664,9 +662,9 @@ bounce_bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map,
curaddr = add_bounce_page(dmat, map, 0, curaddr, 0,
sgsize);
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
buf += sgsize;
buflen -= sgsize;
@ -687,7 +685,7 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
bus_size_t buflen, pmap_t pmap, int flags, bus_dma_segment_t *segs,
int *segp)
{
bus_size_t sgsize, max_sgsize;
bus_size_t sgsize;
vm_paddr_t curaddr;
vm_offset_t kvaddr, vaddr;
int error;
@ -723,21 +721,16 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
/*
* Compute the segment size, and adjust counts.
*/
max_sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = PAGE_SIZE - (curaddr & PAGE_MASK);
sgsize = MIN(buflen, PAGE_SIZE - (curaddr & PAGE_MASK));
if ((dmat->bounce_flags & BUS_DMA_COULD_BOUNCE) != 0 &&
map->pagesneeded != 0 &&
must_bounce(dmat, curaddr)) {
sgsize = roundup2(sgsize, dmat->common.alignment);
sgsize = MIN(sgsize, max_sgsize);
curaddr = add_bounce_page(dmat, map, kvaddr, curaddr, 0,
sgsize);
} else {
sgsize = MIN(sgsize, max_sgsize);
}
sgsize = _bus_dmamap_addseg(dmat, map, curaddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, curaddr, sgsize, segs,
segp))
break;
vaddr += sgsize;
buflen -= sgsize;
@ -756,7 +749,7 @@ bounce_bus_dmamap_load_ma(bus_dma_tag_t dmat, bus_dmamap_t map,
{
vm_paddr_t paddr, next_paddr;
int error, page_index;
bus_size_t sgsize, max_sgsize;
bus_size_t sgsize;
if (dmat->common.flags & BUS_DMA_KEEP_PG_OFFSET) {
/*
@ -790,13 +783,11 @@ bounce_bus_dmamap_load_ma(bus_dma_tag_t dmat, bus_dmamap_t map,
* Compute the segment size, and adjust counts.
*/
paddr = VM_PAGE_TO_PHYS(ma[page_index]) + ma_offs;
max_sgsize = MIN(buflen, dmat->common.maxsegsz);
sgsize = PAGE_SIZE - ma_offs;
sgsize = MIN(buflen, PAGE_SIZE - ma_offs);
if ((dmat->bounce_flags & BUS_DMA_COULD_BOUNCE) != 0 &&
map->pagesneeded != 0 &&
must_bounce(dmat, paddr)) {
sgsize = roundup2(sgsize, dmat->common.alignment);
sgsize = MIN(sgsize, max_sgsize);
KASSERT(vm_addr_align_ok(sgsize,
dmat->common.alignment),
("Segment size is not aligned"));
@ -811,12 +802,9 @@ bounce_bus_dmamap_load_ma(bus_dma_tag_t dmat, bus_dmamap_t map,
next_paddr = 0;
paddr = add_bounce_page(dmat, map, 0, paddr,
next_paddr, sgsize);
} else {
sgsize = MIN(sgsize, max_sgsize);
}
sgsize = _bus_dmamap_addseg(dmat, map, paddr, sgsize, segs,
segp);
if (sgsize == 0)
if (!_bus_dmamap_addsegs(dmat, map, paddr, sgsize, segs,
segp))
break;
KASSERT(buflen >= sgsize,
("Segment length overruns original buffer"));