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>

arch/powerpc/kernel/vdso.c

@@ -113,6 +113,10 @@ static struct vdso_patch_def vdso_patches[] = {
 		CPU_FTR_USE_TB, 0,
 		"__kernel_get_tbfreq", NULL
 	},
+	{
+		CPU_FTR_USE_TB, 0,
+		"__kernel_time", NULL
+	},
 };
 
 /*

arch/powerpc/kernel/vdso32/gettimeofday.S

@@ -180,6 +180,32 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
 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.

arch/powerpc/kernel/vdso32/vdso32.lds.S

@@ -150,6 +150,7 @@ VERSION
 #ifdef CONFIG_PPC64
 		__kernel_getcpu;
 #endif
+		__kernel_time;
 
 	local: *;
 	};

arch/powerpc/kernel/vdso64/gettimeofday.S

@@ -164,6 +164,32 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
   .cfi_endproc
 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	V_LOCAL_FUNC(__get_datapage)
+
+	ld	r4,STAMP_XTIME+TSPC64_TV_SEC(r3)
+
+	cmpldi	r11,0			/* check if t is NULL */
+	beq	2f
+	std	r4,0(r11)		/* store result at *t */
+2:	mtlr	r12
+	crclr	cr0*4+so
+	mr	r3,r4
+	blr
+  .cfi_endproc
+V_FUNCTION_END(__kernel_time)
+
 
 /*
  * This is the core of clock_gettime() and gettimeofday(),

arch/powerpc/kernel/vdso64/vdso64.lds.S

@@ -147,6 +147,7 @@ VERSION
 		__kernel_sync_dicache_p5;
 		__kernel_sigtramp_rt64;
 		__kernel_getcpu;
+		__kernel_time;
 
 	local: *;
 	};