ARM64:VDSO: Improve __do_get_tspec, don't use udiv

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.

Signed-off-by: Andrew Pinski <apinski@cavium.com>
Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev@caviumnetworks.com>

diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index e5caef9e0ec810dce34bd404727f040e55c6f3ae..cd297a72c1a81ca8b63f7715dc02d204cb3840cf 100644 (file)
--- 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