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Subject[RFC PATCH v3 09/12] powerpc/vdso: provide inline alternative to __get_datapage()
Date
__get_datapage() is only a few instructions to retrieve the
address of the page where the kernel stores data to the VDSO.

By inlining this function into its users, a bl/blr pair and
a mflr/mtlr pair is avoided, plus a few reg moves.

The improvement is noticeable (about 55 nsec/call on an 8xx)

With current __get_datapage() function:
gettimeofday: vdso: 731 nsec/call
clock-gettime-realtime-coarse: vdso: 668 nsec/call
clock-gettime-monotonic-coarse: vdso: 745 nsec/call

Using the __get_datapage macro provided by this patch:
gettimeofday: vdso: 677 nsec/call
clock-gettime-realtime-coarse: vdso: 613 nsec/call
clock-gettime-monotonic-coarse: vdso: 690 nsec/call

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/include/asm/vdso_datapage.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
index 4d7965bf369e..7342cc0c1ae4 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -105,6 +105,17 @@ struct vdso_arch_data {

extern struct vdso_arch_data *vdso_data;

+#else /* __ASSEMBLY__ */
+
+.macro get_datapage ptr, offset=0
+ bcl 20, 31, .+4
+ mflr \ptr
+#if CONFIG_PPC_PAGE_SHIFT > 14
+ addis \ptr, \ptr, (_vdso_datapage + \offset - (.-4))@ha
+#endif
+ addi \ptr, \ptr, (_vdso_datapage + \offset - (.-4))@l
+.endm
+
#endif /* __ASSEMBLY__ */

#endif /* __KERNEL__ */
--
2.13.3
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