drivers/dma-buf/heaps/system_heap.c | 33 +++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 9 deletions(-)
From: Barry Song <v-songbaohua@oppo.com>
We can allocate high-order pages, but mapping them one by
one is inefficient. This patch changes the code to map
as large a chunk as possible. The code looks somewhat
complicated mainly because supporting mmap with a
non-zero offset is a bit tricky.
Using the micro-benchmark below, we see that mmap becomes
3.5X faster:
#include <stdio.h>
#include <fcntl.h>
#include <linux/dma-heap.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include <stdlib.h>
#define SIZE (512UL * 1024 * 1024)
#define PAGE 4096
#define STRIDE (PAGE/sizeof(int))
#define PAGES (SIZE/PAGE)
int main(void) {
int heap = open("/dev/dma_heap/system", O_RDONLY);
struct dma_heap_allocation_data d =
{ .len = SIZE, .fd_flags = O_RDWR|O_CLOEXEC };
ioctl(heap, DMA_HEAP_IOCTL_ALLOC, &d);
struct timespec t0, t1;
clock_gettime(CLOCK_MONOTONIC, &t0);
int *p = mmap(NULL, SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, d.fd, 0);
clock_gettime(CLOCK_MONOTONIC, &t1);
for (int i = 0; i < PAGES; i++) p[i*STRIDE] = i;
for (int i = 0; i < PAGES; i++)
if (p[i*STRIDE] != i) {
fprintf(stderr, "mismatch at page %d\n", i);
exit(1);
}
long ns = (t1.tv_sec-t0.tv_sec)*1000000000L +
(t1.tv_nsec-t0.tv_nsec);
printf("mmap 512MB took %.3f us, verify OK\n", ns/1000.0);
return 0;
}
W/ patch:
~ # ./a.out
mmap 512MB took 200266.000 us, verify OK
~ # ./a.out
mmap 512MB took 198151.000 us, verify OK
~ # ./a.out
mmap 512MB took 197069.000 us, verify OK
~ # ./a.out
mmap 512MB took 196781.000 us, verify OK
~ # ./a.out
mmap 512MB took 198102.000 us, verify OK
~ # ./a.out
mmap 512MB took 195552.000 us, verify OK
W/o patch:
~ # ./a.out
mmap 512MB took 6987470.000 us, verify OK
~ # ./a.out
mmap 512MB took 6970739.000 us, verify OK
~ # ./a.out
mmap 512MB took 6984383.000 us, verify OK
~ # ./a.out
mmap 512MB took 6971311.000 us, verify OK
~ # ./a.out
mmap 512MB took 6991680.000 us, verify OK
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: John Stultz <jstultz@google.com>
---
-v2: collect John's ack. thanks!
drivers/dma-buf/heaps/system_heap.c | 33 +++++++++++++++++++++--------
1 file changed, 24 insertions(+), 9 deletions(-)
diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index bbe7881f1360..4c782fe33fd4 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -186,20 +186,35 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
struct system_heap_buffer *buffer = dmabuf->priv;
struct sg_table *table = &buffer->sg_table;
unsigned long addr = vma->vm_start;
- struct sg_page_iter piter;
- int ret;
+ unsigned long pgoff = vma->vm_pgoff;
+ struct scatterlist *sg;
+ int i, ret;
+
+ for_each_sgtable_sg(table, sg, i) {
+ unsigned long n = sg->length >> PAGE_SHIFT;
- for_each_sgtable_page(table, &piter, vma->vm_pgoff) {
- struct page *page = sg_page_iter_page(&piter);
+ if (pgoff < n)
+ break;
+ pgoff -= n;
+ }
+
+ for (; sg && addr < vma->vm_end; sg = sg_next(sg)) {
+ unsigned long n = (sg->length >> PAGE_SHIFT) - pgoff;
+ struct page *page = sg_page(sg) + pgoff;
+ unsigned long size = n << PAGE_SHIFT;
+
+ if (addr + size > vma->vm_end)
+ size = vma->vm_end - addr;
- ret = remap_pfn_range(vma, addr, page_to_pfn(page), PAGE_SIZE,
- vma->vm_page_prot);
+ ret = remap_pfn_range(vma, addr, page_to_pfn(page),
+ size, vma->vm_page_prot);
if (ret)
return ret;
- addr += PAGE_SIZE;
- if (addr >= vma->vm_end)
- return 0;
+
+ addr += size;
+ pgoff = 0;
}
+
return 0;
}
--
2.39.3 (Apple Git-146)Hi Sumit, > > Using the micro-benchmark below, we see that mmap becomes > 3.5X faster: Marcin pointed out to me off-tree that it is actually 35x faster, not 3.5x faster. Sorry for my poor math. I assume you can fix this when merging it? > > W/ patch: > > ~ # ./a.out > mmap 512MB took 200266.000 us, verify OK > ~ # ./a.out > mmap 512MB took 198151.000 us, verify OK > ~ # ./a.out > mmap 512MB took 197069.000 us, verify OK > ~ # ./a.out > mmap 512MB took 196781.000 us, verify OK > ~ # ./a.out > mmap 512MB took 198102.000 us, verify OK > ~ # ./a.out > mmap 512MB took 195552.000 us, verify OK > > W/o patch: > > ~ # ./a.out > mmap 512MB took 6987470.000 us, verify OK > ~ # ./a.out > mmap 512MB took 6970739.000 us, verify OK > ~ # ./a.out > mmap 512MB took 6984383.000 us, verify OK > ~ # ./a.out > mmap 512MB took 6971311.000 us, verify OK > ~ # ./a.out > mmap 512MB took 6991680.000 us, verify OK Thanks Barry
Hi Barry, On Fri, 21 Nov 2025 at 06:54, Barry Song <21cnbao@gmail.com> wrote: > > Hi Sumit, > > > > > Using the micro-benchmark below, we see that mmap becomes > > 3.5X faster: > > > Marcin pointed out to me off-tree that it is actually 35x faster, > not 3.5x faster. Sorry for my poor math. I assume you can fix this > when merging it? Sure, I corrected this, and is merged to drm-misc-next Thanks, Sumit. > > > > > W/ patch: > > > > ~ # ./a.out > > mmap 512MB took 200266.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 198151.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 197069.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 196781.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 198102.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 195552.000 us, verify OK > > > > W/o patch: > > > > ~ # ./a.out > > mmap 512MB took 6987470.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 6970739.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 6984383.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 6971311.000 us, verify OK > > ~ # ./a.out > > mmap 512MB took 6991680.000 us, verify OK > > > Thanks > Barry
On Tue, 21 Oct 2025 17:20:22 +1300, Barry Song wrote: > From: Barry Song <v-songbaohua@oppo.com> > > We can allocate high-order pages, but mapping them one by > one is inefficient. This patch changes the code to map > as large a chunk as possible. The code looks somewhat > > [ ... ] Reviewed-by: Maxime Ripard <mripard@kernel.org> Thanks! Maxime
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