mirror of
https://github.com/torvalds/linux.git
synced 2025-12-07 20:06:24 +00:00
04c7adb587
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
35X 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>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
[sumits: correct from 3.5x to 35x]
Link: https://patch.msgid.link/20251021042022.47919-1-21cnbao@gmail.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.