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    Subject[RFC PATCH v3 09/12] powerpc/vdso: provide inline alternative to __get_datapage()
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    __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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