[PATCH] ARM: DMA-mapping: mark all !DMA_TO_DEVICE pages in unmapping as clean

[Ming Lei]

It is common for one sg to include many pages, so mark all these
pages as clean to avoid unnecessary flushing on them in
set_pte_at() or update_mmu_cache().

The patch might improve loading performance of applciation code a bit.

On the below test code to read file(~1GByte size) from usb mass storage
disk to buffer created with mmap(PROT_READ | PROT_EXEC) on
Pandaboard, average ~1% improvement can be observed with the patch on
10 times test.


#define _GNU_SOURCE

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <string.h>
#include <assert.h>

unsigned int sum = 0;

static unsigned long tv_diff(struct timeval *tv1, struct timeval *tv2)
{
	return (tv2->tv_sec - tv1->tv_sec) * 1000000 +
		(tv2->tv_usec - tv1->tv_usec);
}

int main(int argc, char *argv[])
{
	char *mbuffer;
	int fd;
	int i;
	unsigned long page_size, size;
	struct stat stat;
	struct timeval t1, t2;

	page_size = getpagesize();
	fd = open(argv[1], O_RDONLY);
	assert(fd >= 0);

	fstat(fd, &stat);
	size = stat.st_size;
	printf("%s: file %s, file size %lu, page size %lu\n", argv[0],
		read_filename, size, page_size);

	gettimeofday(&t1, NULL);
	mbuffer = mmap(NULL, size, PROT_READ | PROT_EXEC, MAP_SHARED, fd, 0);
	for (i = 0 ; i < size ; i += page_size)
		sum += mbuffer[i];
	munmap(mbuffer, page_size);
	gettimeofday(&t2, NULL);
	printf("\tread mmaped time: %luus\n", tv_diff(&t1, &t2));

	close(fd);
}

Cc: Nicolas Pitre <nicolas.pitre at linaro.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Marek Szyprowski <m.szyprowski at samsung.com>
Cc: Russell King <linux at arm.linux.org.uk>
Signed-off-by: Ming Lei <ming.lei at canonical.com>
---
 arch/arm/mm/dma-mapping.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index e9db6b4..e63124a 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -879,10 +879,23 @@ static void __dma_page_dev_to_cpu(struct page *page, unsigned long off,
 	dma_cache_maint_page(page, off, size, dir, dmac_unmap_area);
 
 	/*
-	 * Mark the D-cache clean for this page to avoid extra flushing.
+	 * Mark the D-cache clean for these pages to avoid extra flushing.
 	 */
-	if (dir != DMA_TO_DEVICE && off == 0 && size >= PAGE_SIZE)
-		set_bit(PG_dcache_clean, &page->flags);
+	if (dir != DMA_TO_DEVICE && size >= PAGE_SIZE) {
+		unsigned long pfn;
+		size_t left = size;
+
+		pfn = page_to_pfn(page);
+		if (off) {
+			pfn++;
+			left -= PAGE_SIZE - off % PAGE_SIZE;
+		}
+		while (left >= PAGE_SIZE) {
+			page = pfn_to_page(pfn++);
+			set_bit(PG_dcache_clean, &page->flags);
+			left -= PAGE_SIZE;
+		}
+	}
 }
 
 /**
-- 
1.7.9.5