[PATCH] powerpc/vdso64: inline __get_datapage()
Christophe Leroy
christophe.leroy at c-s.fr
Wed Aug 21 19:46:38 AEST 2019
Le 21/08/2019 à 11:29, Santosh Sivaraj a écrit :
> __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.
>
> clock-gettime-monotonic: syscall: 514 nsec/call 396 nsec/call
> clock-gettime-monotonic: libc: 25 nsec/call 24 nsec/call
> clock-gettime-monotonic: vdso: 20 nsec/call 20 nsec/call
> clock-getres-monotonic: syscall: 347 nsec/call 372 nsec/call
> clock-getres-monotonic: libc: 19 nsec/call 19 nsec/call
> clock-getres-monotonic: vdso: 10 nsec/call 10 nsec/call
> clock-gettime-monotonic-coarse: syscall: 511 nsec/call 396 nsec/call
> clock-gettime-monotonic-coarse: libc: 23 nsec/call 21 nsec/call
> clock-gettime-monotonic-coarse: vdso: 15 nsec/call 13 nsec/call
> clock-gettime-realtime: syscall: 526 nsec/call 405 nsec/call
> clock-gettime-realtime: libc: 24 nsec/call 23 nsec/call
> clock-gettime-realtime: vdso: 18 nsec/call 18 nsec/call
> clock-getres-realtime: syscall: 342 nsec/call 372 nsec/call
> clock-getres-realtime: libc: 19 nsec/call 19 nsec/call
> clock-getres-realtime: vdso: 10 nsec/call 10 nsec/call
> clock-gettime-realtime-coarse: syscall: 515 nsec/call 373 nsec/call
> clock-gettime-realtime-coarse: libc: 23 nsec/call 22 nsec/call
> clock-gettime-realtime-coarse: vdso: 14 nsec/call 13 nsec/call
I think you should only put the measurements on vdso calls, and only the
ones that are impacted by the change. For exemple, getres function
doesn't use __get_datapage so showing it here is pointless.
gettimeofday should be shown there as it uses __get_datapage()
>
> Based on the patch by Christophe Leroy <christophe.leroy at c-s.fr> for vdso32.
>
> Signed-off-by: Santosh Sivaraj <santosh at fossix.org>
> ---
>
> except for a couple of calls (1 or 2 nsec reduction), there are no
> improvements in the call times. Or is 10 nsec the minimum granularity??
Maybe the ones that show no improvements are the ones that don't use
__get_datapage() at all ...
>
> So I don't know if its even worth updating vdso64 except to keep vdso32 and
> vdso64 equal.
2ns on a 15ns call is 13% so it is worth it I think.
Christophe
>
>
> arch/powerpc/kernel/vdso64/cacheflush.S | 10 ++++----
> arch/powerpc/kernel/vdso64/datapage.S | 29 ++++-------------------
> arch/powerpc/kernel/vdso64/datapage.h | 10 ++++++++
> arch/powerpc/kernel/vdso64/gettimeofday.S | 8 ++++---
> 4 files changed, 24 insertions(+), 33 deletions(-)
> create mode 100644 arch/powerpc/kernel/vdso64/datapage.h
>
> diff --git a/arch/powerpc/kernel/vdso64/cacheflush.S b/arch/powerpc/kernel/vdso64/cacheflush.S
> index 3f92561a64c4..30e8b0d29bea 100644
> --- a/arch/powerpc/kernel/vdso64/cacheflush.S
> +++ b/arch/powerpc/kernel/vdso64/cacheflush.S
> @@ -10,6 +10,8 @@
> #include <asm/vdso.h>
> #include <asm/asm-offsets.h>
>
> +#include "datapage.h"
> +
> .text
>
> /*
> @@ -24,14 +26,12 @@ V_FUNCTION_BEGIN(__kernel_sync_dicache)
> .cfi_startproc
> mflr r12
> .cfi_register lr,r12
> - mr r11,r3
> - bl V_LOCAL_FUNC(__get_datapage)
> + get_datapage r11, 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 +48,7 @@ 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/vdso64/datapage.S b/arch/powerpc/kernel/vdso64/datapage.S
> index dc84f5ae3802..8712f57c931c 100644
> --- a/arch/powerpc/kernel/vdso64/datapage.S
> +++ b/arch/powerpc/kernel/vdso64/datapage.S
> @@ -11,34 +11,13 @@
> #include <asm/unistd.h>
> #include <asm/vdso.h>
>
> +#include "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 +32,7 @@ V_FUNCTION_BEGIN(__kernel_get_syscall_map)
> mflr r12
> .cfi_register lr,r12
> mr r4,r3
> - bl V_LOCAL_FUNC(__get_datapage)
> + get_datapage r3, r0
> mtlr r12
> addi r3,r3,CFG_SYSCALL_MAP64
> cmpldi cr0,r4,0
> @@ -75,7 +54,7 @@ V_FUNCTION_BEGIN(__kernel_get_tbfreq)
> .cfi_startproc
> mflr r12
> .cfi_register lr,r12
> - bl V_LOCAL_FUNC(__get_datapage)
> + get_datapage r3, r0
> ld r3,CFG_TB_TICKS_PER_SEC(r3)
> mtlr r12
> crclr cr0*4+so
> diff --git a/arch/powerpc/kernel/vdso64/datapage.h b/arch/powerpc/kernel/vdso64/datapage.h
> new file mode 100644
> index 000000000000..f2f0da0f65f3
> --- /dev/null
> +++ b/arch/powerpc/kernel/vdso64/datapage.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +.macro get_datapage ptr, tmp
> + bcl 20,31,888f
> +888:
> + mflr \ptr
> + addi \ptr, \ptr, __kernel_datapage_offset - 888b
> + lwz \tmp, 0(\ptr)
> + add \ptr, \tmp, \ptr
> +.endm
> diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S b/arch/powerpc/kernel/vdso64/gettimeofday.S
> index 07bfe33fe874..7bcc879392cc 100644
> --- a/arch/powerpc/kernel/vdso64/gettimeofday.S
> +++ b/arch/powerpc/kernel/vdso64/gettimeofday.S
> @@ -12,6 +12,8 @@
> #include <asm/asm-offsets.h>
> #include <asm/unistd.h>
>
> +#include "datapage.h"
> +
> .text
> /*
> * Exact prototype of gettimeofday
> @@ -26,7 +28,7 @@ V_FUNCTION_BEGIN(__kernel_gettimeofday)
>
> mr r11,r3 /* r11 holds tv */
> mr r10,r4 /* r10 holds tz */
> - bl V_LOCAL_FUNC(__get_datapage) /* get data page */
> + get_datapage r3, r0
> cmpldi r11,0 /* check if tv is NULL */
> beq 2f
> lis r7,1000000 at ha /* load up USEC_PER_SEC */
> @@ -71,7 +73,7 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
> mflr r12 /* r12 saves lr */
> .cfi_register lr,r12
> mr r11,r4 /* r11 saves tp */
> - bl V_LOCAL_FUNC(__get_datapage) /* get data page */
> + get_datapage r3, r0 /* get data page */
> lis r7,NSEC_PER_SEC at h /* want nanoseconds */
> ori r7,r7,NSEC_PER_SEC at l
> beq cr5,70f
> @@ -218,7 +220,7 @@ V_FUNCTION_BEGIN(__kernel_time)
> .cfi_register lr,r12
>
> mr r11,r3 /* r11 holds t */
> - bl V_LOCAL_FUNC(__get_datapage)
> + get_datapage r3, r0
>
> ld r4,STAMP_XTIME+TSPC64_TV_SEC(r3)
>
>
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