From: Andrew Pinski apinski@cavium.com
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 --- arch/arm64/kernel/vdso/gettimeofday.S | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S index e5caef9..cd297a7 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