powerpc: Add VDSO version of time

On 04/18/2013 07:38 PM, Anton Blanchard wrote:
> Since you are only reading one long you shouldn't need to check the
> update count and loop, you will always see a consistent value. The
> system call version of time() just does an unprotected load for example.

Fixed.

> With the above change and with Michael's comments covered (decent
> changelog entry and Signed-off-by):
>
> Acked-by: Anton Blanchard <anton@samba.org>

Thanks for the review, below the updated patch:

From: Adhemerval Zanella <azanella@linux.vnet.ibm.com>

This patch implement the time syscall as vDSO. The performance speedups
are:

Baseline PPC32: 380 nsec
Baseline PPC64: 350 nsec
vdso PPC32:      20 nsec
vsdo PPC64:      20 nsec

Tested on 64 bit build with both 32 bit and 64 bit userland.

Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Adhemerval Zanella <azanella@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S b/arch/powerpc/kernel/vdso32/gettimeofday.S
index 4ee09ee2e836..27e2f623210b 100644
--- a/arch/powerpc/kernel/vdso32/gettimeofday.S
+++ b/arch/powerpc/kernel/vdso32/gettimeofday.S
@@ -181,6 +181,32 @@ V_FUNCTION_END(__kernel_clock_getres)
 
 
 /*
+ * Exact prototype of time()
+ *
+ * time_t time(time *t);
+ *
+ */
+V_FUNCTION_BEGIN(__kernel_time)
+  .cfi_startproc
+        mflr    r12
+  .cfi_register lr,r12
+
+        mr      r11,r3                  /* r11 holds t */
+        bl      __get_datapage@local
+        mr      r9, r3                  /* datapage ptr in r9 */
+
+        lwz     r3,STAMP_XTIME+TSPEC_TV_SEC(r9)
+
+        cmplwi  r11,0                   /* check if t is NULL */
+        beq     2f
+        stw     r3,0(r11)               /* store result at *t */
+2:      mtlr    r12
+        crclr   cr0*4+so
+        blr
+  .cfi_endproc
+V_FUNCTION_END(__kernel_time)
+
+/*
  * This is the core of clock_gettime() and gettimeofday(),
  * it returns the current time in r3 (seconds) and r4.
  * On entry, r7 gives the resolution of r4, either USEC_PER_SEC