Re: [PATCH v3 4/8] powerpc/vdso32: inline __get_datapage()

From: Michael Ellerman
Date: Thu Nov 21 2019 - 20:58:37 EST

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Christophe Leroy <christophe.leroy@xxxxxx> writes:
> __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)
>
> vdsotest before the patch:
> gettimeofday: vdso: 731 nsec/call
> clock-gettime-realtime-coarse: vdso: 668 nsec/call
> clock-gettime-monotonic-coarse: vdso: 745 nsec/call
>
> vdsotest after the 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@xxxxxx>

This doesn't build with gcc 4.6.3:

/linux/arch/powerpc/kernel/vdso32/gettimeofday.S: Assembler messages:
/linux/arch/powerpc/kernel/vdso32/gettimeofday.S:41: Error: unsupported relocation against __kernel_datapage_offset
/linux/arch/powerpc/kernel/vdso32/gettimeofday.S:86: Error: unsupported relocation against __kernel_datapage_offset
/linux/arch/powerpc/kernel/vdso32/gettimeofday.S:213: Error: unsupported relocation against __kernel_datapage_offset
/linux/arch/powerpc/kernel/vdso32/gettimeofday.S:247: Error: unsupported relocation against __kernel_datapage_offset
make[4]: *** [arch/powerpc/kernel/vdso32/gettimeofday.o] Error 1

https://travis-ci.org/linuxppc/linux/jobs/614904530

cheers

> ---
> v3: define get_datapage macro in asm/vdso_datapage.h
> ---
> arch/powerpc/include/asm/vdso_datapage.h | 10 ++++++++++
> arch/powerpc/kernel/vdso32/cacheflush.S | 9 ++++-----
> arch/powerpc/kernel/vdso32/datapage.S | 28 +++-------------------------
> arch/powerpc/kernel/vdso32/gettimeofday.S | 12 +++++-------
> 4 files changed, 22 insertions(+), 37 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
> index 2ccb938d8544..da3d2de817f6 100644
> --- a/arch/powerpc/include/asm/vdso_datapage.h
> +++ b/arch/powerpc/include/asm/vdso_datapage.h
> @@ -116,6 +116,16 @@ struct vdso_data {
>
> extern struct vdso_data *vdso_data;
>
> +#else /* __ASSEMBLY__ */
> +
> +.macro get_datapage ptr, tmp
> + bcl 20, 31, .+4
> + mflr \ptr
> + addi \ptr, \ptr, __kernel_datapage_offset - (.-4)
> + lwz \tmp, 0(\ptr)
> + add \ptr, \tmp, \ptr
> +.endm
> +
> #endif /* __ASSEMBLY__ */
>
> #endif /* __KERNEL__ */
> diff --git a/arch/powerpc/kernel/vdso32/cacheflush.S b/arch/powerpc/kernel/vdso32/cacheflush.S
> index 7f882e7b9f43..d178ec8c279d 100644
> --- a/arch/powerpc/kernel/vdso32/cacheflush.S
> +++ b/arch/powerpc/kernel/vdso32/cacheflush.S
> @@ -8,6 +8,7 @@
> #include <asm/processor.h>
> #include <asm/ppc_asm.h>
> #include <asm/vdso.h>
> +#include <asm/vdso_datapage.h>
> #include <asm/asm-offsets.h>
>
> .text
> @@ -24,14 +25,12 @@ V_FUNCTION_BEGIN(__kernel_sync_dicache)
> .cfi_startproc
> mflr r12
> .cfi_register lr,r12
> - mr r11,r3
> - bl __get_datapage@local
> + get_datapage r10, r0
> mtlr r12
> - mr r10,r3
>
> lwz r7,CFG_DCACHE_BLOCKSZ(r10)
> addi r5,r7,-1
> - andc r6,r11,r5 /* round low to line bdy */
> + andc r6,r3,r5 /* round low to line bdy */
> subf r8,r6,r4 /* compute length */
> add r8,r8,r5 /* ensure we get enough */
> lwz r9,CFG_DCACHE_LOGBLOCKSZ(r10)
> @@ -48,7 +47,7 @@ V_FUNCTION_BEGIN(__kernel_sync_dicache)
>
> lwz r7,CFG_ICACHE_BLOCKSZ(r10)
> addi r5,r7,-1
> - andc r6,r11,r5 /* round low to line bdy */
> + andc r6,r3,r5 /* round low to line bdy */
> subf r8,r6,r4 /* compute length */
> add r8,r8,r5
> lwz r9,CFG_ICACHE_LOGBLOCKSZ(r10)
> diff --git a/arch/powerpc/kernel/vdso32/datapage.S b/arch/powerpc/kernel/vdso32/datapage.S
> index 6c7401bd284e..1095d818f94a 100644
> --- a/arch/powerpc/kernel/vdso32/datapage.S
> +++ b/arch/powerpc/kernel/vdso32/datapage.S
> @@ -10,35 +10,13 @@
> #include <asm/asm-offsets.h>
> #include <asm/unistd.h>
> #include <asm/vdso.h>
> +#include <asm/vdso_datapage.h>
>
> .text
> .global __kernel_datapage_offset;
> __kernel_datapage_offset:
> .long 0
>
> -V_FUNCTION_BEGIN(__get_datapage)
> - .cfi_startproc
> - /* We don't want that exposed or overridable as we want other objects
> - * to be able to bl directly to here
> - */
> - .protected __get_datapage
> - .hidden __get_datapage
> -
> - mflr r0
> - .cfi_register lr,r0
> -
> - bcl 20,31,data_page_branch
> -data_page_branch:
> - mflr r3
> - mtlr r0
> - addi r3, r3, __kernel_datapage_offset-data_page_branch
> - lwz r0,0(r3)
> - .cfi_restore lr
> - add r3,r0,r3
> - blr
> - .cfi_endproc
> -V_FUNCTION_END(__get_datapage)
> -
> /*
> * void *__kernel_get_syscall_map(unsigned int *syscall_count) ;
> *
> @@ -53,7 +31,7 @@ V_FUNCTION_BEGIN(__kernel_get_syscall_map)
> mflr r12
> .cfi_register lr,r12
> mr r4,r3
> - bl __get_datapage@local
> + get_datapage r3, r0
> mtlr r12
> addi r3,r3,CFG_SYSCALL_MAP32
> cmpli cr0,r4,0
> @@ -75,7 +53,7 @@ V_FUNCTION_BEGIN(__kernel_get_tbfreq)
> .cfi_startproc
> mflr r12
> .cfi_register lr,r12
> - bl __get_datapage@local
> + get_datapage r3, r0
> lwz r4,(CFG_TB_TICKS_PER_SEC + 4)(r3)
> lwz r3,CFG_TB_TICKS_PER_SEC(r3)
> mtlr r12
> diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S b/arch/powerpc/kernel/vdso32/gettimeofday.S
> index 355b537d327a..9867c7b9a25a 100644
> --- a/arch/powerpc/kernel/vdso32/gettimeofday.S
> +++ b/arch/powerpc/kernel/vdso32/gettimeofday.S
> @@ -9,6 +9,7 @@
> #include <asm/processor.h>
> #include <asm/ppc_asm.h>
> #include <asm/vdso.h>
> +#include <asm/vdso_datapage.h>
> #include <asm/asm-offsets.h>
> #include <asm/unistd.h>
>
> @@ -35,8 +36,7 @@ V_FUNCTION_BEGIN(__kernel_gettimeofday)
>
> mr r10,r3 /* r10 saves tv */
> mr r11,r4 /* r11 saves tz */
> - bl __get_datapage@local /* get data page */
> - mr r9, r3 /* datapage ptr in r9 */
> + get_datapage r9, r0
> cmplwi r10,0 /* check if tv is NULL */
> beq 3f
> lis r7,1000000@ha /* load up USEC_PER_SEC */
> @@ -82,8 +82,7 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
> mflr r12 /* r12 saves lr */
> .cfi_register lr,r12
> mr r11,r4 /* r11 saves tp */
> - bl __get_datapage@local /* get data page */
> - mr r9,r3 /* datapage ptr in r9 */
> + get_datapage r9, r0
> lis r7,NSEC_PER_SEC@h /* want nanoseconds */
> ori r7,r7,NSEC_PER_SEC@l
> beq cr5, .Lcoarse_clocks
> @@ -208,7 +207,7 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
>
> mflr r12
> .cfi_register lr,r12
> - bl __get_datapage@local /* get data page */
> + get_datapage r3, r0
> lwz r5, CLOCK_HRTIMER_RES(r3)
> mtlr r12
> li r3,0
> @@ -242,8 +241,7 @@ V_FUNCTION_BEGIN(__kernel_time)
> .cfi_register lr,r12
>
> mr r11,r3 /* r11 holds t */
> - bl __get_datapage@local
> - mr r9, r3 /* datapage ptr in r9 */
> + get_datapage r9, r0
>
> lwz r3,STAMP_XTIME+TSPEC_TV_SEC(r9)
>
> --
> 2.13.3

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