In most other targets (x86/tile for an example),
the division in __do_get_tspec is converted into
a simple loop. The main reason for this is
because the result of this division is going
to be either 0 or 1.
This changes the division to the simple loop
and thus speeding up gettimeofday.
On ThunderX, this speeds up gettimeofday by 16.6%.
Signed-off-by: Andrew Pinski <apin...@cavium.com>
---
arch/arm64/kernel/vdso/gettimeofday.S | 27 +++++++++++++++++++--------
1 files changed, 19 insertions(+), 8 deletions(-)
diff --git a/arch/arm64/kernel/vdso/gettimeofday.S
b/arch/arm64/kernel/vdso/gettimeofday.S
index e5caef9..28f4da7 100644
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -246,14 +246,25 @@ ENTRY(__do_get_tspec)
mul x10, x10, x11
/* Use the kernel time to calculate the new timespec. */
- mov x11, #NSEC_PER_SEC_LO16
- movk x11, #NSEC_PER_SEC_HI16, lsl #16
- lsl x11, x11, x12
- add x15, x10, x14
- udiv x14, x15, x11
- add x10, x13, x14
- mul x13, x14, x11
- sub x11, x15, x13
+ mov x15, #NSEC_PER_SEC_LO16
+ movk x15, #NSEC_PER_SEC_HI16, lsl #16
+ lsl x15, x15, x12
+ add x11, x10, x14
+ mov x10, x13
+
+ /*
+ * Use a loop instead of a division as this is most
+ * likely going to be only giving a 1 or 0 and that is faster
+ * than a division.
+ */
+ cmp x11, x15
+ b.lt 1f
+2:
+ sub x11, x11, x15
+ add x10, x10, 1
+ cmp x11, x15
+ b.ge 2b
+1:
ret
.cfi_endproc
--
1.7.2.5
