A profile of a network benchmark showed iommu_num_pages rather high up:
0.52% iommu_num_pages
Looking at the profile, an integer divide is taking almost all of the time:
%
: c000000000376ea4 <.iommu_num_pages>:
1.93 : c000000000376ea4: fb e1 ff f8 std r31,-8(r1)
0.00 : c000000000376ea8: f8 21 ff c1 stdu r1,-64(r1)
0.00 : c000000000376eac: 7c 3f 0b 78 mr r31,r1
3.86 : c000000000376eb0: 38 84 ff ff addi r4,r4,-1
0.00 : c000000000376eb4: 38 05 ff ff addi r0,r5,-1
0.00 : c000000000376eb8: 7c 84 2a 14 add r4,r4,r5
46.95 : c000000000376ebc: 7c 00 18 38 and r0,r0,r3
45.66 : c000000000376ec0: 7c 84 02 14 add r4,r4,r0
0.00 : c000000000376ec4: 7c 64 2b 92 divdu r3,r4,r5
0.00 : c000000000376ec8: 38 3f 00 40 addi r1,r31,64
0.00 : c000000000376ecc: eb e1 ff f8 ld r31,-8(r1)
1.61 : c000000000376ed0: 4e 80 00 20 blr
Since every caller of iommu_num_pages passes in a constant power of two
we can inline this such that the divide is replaced by a shift. The
entire function is only a few instructions once optimised, so it is
a good candidate for inlining overall.
Signed-off-by: Anton Blanchard <[email protected]>
--
Index: powerpc.git/include/linux/iommu-helper.h
===================================================================
--- powerpc.git.orig/include/linux/iommu-helper.h 2010-07-30 11:51:49.900741505 +1000
+++ powerpc.git/include/linux/iommu-helper.h 2010-07-30 11:53:49.310741623 +1000
@@ -1,6 +1,8 @@
#ifndef _LINUX_IOMMU_HELPER_H
#define _LINUX_IOMMU_HELPER_H
+#include <linux/kernel.h>
+
static inline unsigned long iommu_device_max_index(unsigned long size,
unsigned long offset,
u64 dma_mask)
@@ -20,7 +22,13 @@ extern unsigned long iommu_area_alloc(un
unsigned long boundary_size,
unsigned long align_mask);
-extern unsigned long iommu_num_pages(unsigned long addr, unsigned long len,
- unsigned long io_page_size);
+static inline unsigned long iommu_num_pages(unsigned long addr,
+ unsigned long len,
+ unsigned long io_page_size)
+{
+ unsigned long size = (addr & (io_page_size - 1)) + len;
+
+ return DIV_ROUND_UP(size, io_page_size);
+}
#endif
Index: powerpc.git/lib/iommu-helper.c
===================================================================
--- powerpc.git.orig/lib/iommu-helper.c 2010-07-30 11:45:10.860741495 +1000
+++ powerpc.git/lib/iommu-helper.c 2010-07-30 11:52:20.732001414 +1000
@@ -38,12 +38,3 @@ again:
return -1;
}
EXPORT_SYMBOL(iommu_area_alloc);
-
-unsigned long iommu_num_pages(unsigned long addr, unsigned long len,
- unsigned long io_page_size)
-{
- unsigned long size = (addr & (io_page_size - 1)) + len;
-
- return DIV_ROUND_UP(size, io_page_size);
-}
-EXPORT_SYMBOL(iommu_num_pages);