Messages in this thread Patch in this message | | | From | Christophe Leroy <> | Subject | [PATCH v4 3/4] powerpc/lib: implement strlen() in assembly | Date | Fri, 8 Jun 2018 10:20:41 +0000 (UTC) |
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The generic implementation of strlen() reads strings byte per byte.
This patch implements strlen() in assembly based on a read of entire words, in the same spirit as what some other arches and glibc do.
On a 8xx the time spent in strlen is reduced by 2/3 for long strings.
strlen() selftest on an 8xx provides the following values:
Before the patch (ie with the generic strlen() in lib/string.c):
len 256 : time = 0.803648 len 16 : time = 0.062989 len 4 : time = 0.026269
After the patch:
len 256 : time = 0.267791 ==> 66% improvment len 16 : time = 0.037902 ==> 41% improvment len 4 : time = 0.026124 ==> no degradation
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> --- Not tested on PPC64.
Changes in v4: - Added alignment of the loop - doing the andc only if still not 0 as it happends only for bytes above 0x7f which is pretty rare in a string
Changes in v3: - Made it common to PPC32 and PPC64
Changes in v2: - Moved handling of unaligned strings outside of the main path as it is very unlikely. - Removed the verification of the fourth byte in case none of the three first ones are NUL.
arch/powerpc/include/asm/asm-compat.h | 4 +++ arch/powerpc/include/asm/string.h | 1 + arch/powerpc/lib/string.S | 57 +++++++++++++++++++++++++++++++++++ 3 files changed, 62 insertions(+)
diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h index 7f2a7702596c..0e99fe7570c0 100644 --- a/arch/powerpc/include/asm/asm-compat.h +++ b/arch/powerpc/include/asm/asm-compat.h @@ -20,8 +20,10 @@ /* operations for longs and pointers */ #define PPC_LL stringify_in_c(ld) +#define PPC_LLU stringify_in_c(ldu) #define PPC_STL stringify_in_c(std) #define PPC_STLU stringify_in_c(stdu) +#define PPC_ROTLI stringify_in_c(rotldi) #define PPC_LCMPI stringify_in_c(cmpdi) #define PPC_LCMPLI stringify_in_c(cmpldi) #define PPC_LCMP stringify_in_c(cmpd) @@ -53,8 +55,10 @@ /* operations for longs and pointers */ #define PPC_LL stringify_in_c(lwz) +#define PPC_LLU stringify_in_c(lwzu) #define PPC_STL stringify_in_c(stw) #define PPC_STLU stringify_in_c(stwu) +#define PPC_ROTLI stringify_in_c(rotlwi) #define PPC_LCMPI stringify_in_c(cmpwi) #define PPC_LCMPLI stringify_in_c(cmplwi) #define PPC_LCMP stringify_in_c(cmpw) diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h index 9b8cedf618f4..8fdcb532de72 100644 --- a/arch/powerpc/include/asm/string.h +++ b/arch/powerpc/include/asm/string.h @@ -13,6 +13,7 @@ #define __HAVE_ARCH_MEMCHR #define __HAVE_ARCH_MEMSET16 #define __HAVE_ARCH_MEMCPY_FLUSHCACHE +#define __HAVE_ARCH_STRLEN extern char * strcpy(char *,const char *); extern char * strncpy(char *,const char *, __kernel_size_t); diff --git a/arch/powerpc/lib/string.S b/arch/powerpc/lib/string.S index 4b41970e9ed8..238f61e2024f 100644 --- a/arch/powerpc/lib/string.S +++ b/arch/powerpc/lib/string.S @@ -67,3 +67,60 @@ _GLOBAL(memchr) 2: li r3,0 blr EXPORT_SYMBOL(memchr) + +_GLOBAL(strlen) + andi. r9, r3, (SZL - 1) + addi r10, r3, -SZL + bne- 1f +2: lis r6, 0x8080 + ori r6, r6, 0x8080 /* r6 = 0x80808080 (himagic) */ +#ifdef CONFIG_PPC64 + rldimi r6, r6, 32, 0 /* r6 = 0x8080808080808080 (himagic) */ +#endif + PPC_ROTLI r7, r6, 1 /* r7 = 0x01010101(01010101) (lomagic)*/ + .balign IFETCH_ALIGN_BYTES +3: PPC_LLU r9, SZL(r10) + /* ((x - lomagic) & ~x & himagic) == 0 means no byte in x is NUL */ + subf r8, r7, r9 + and. r8, r8, r6 + beq+ 3b + andc. r8, r8, r9 + beq+ 3b +#ifdef CONFIG_PPC64 + rldicl. r8, r9, 8, 56 + beq 20f + rldicl. r8, r9, 16, 56 + beq 21f + rldicl. r8, r9, 24, 56 + beq 22f + rldicl. r8, r9, 32, 56 + beq 23f + addi r10, r10, 4 +#endif + rlwinm. r8, r9, 0, 0xff000000 + beq 20f + rlwinm. r8, r9, 0, 0x00ff0000 + beq 21f + rlwinm. r8, r9, 0, 0x0000ff00 + beq 22f +23: subf r3, r3, r10 + addi r3, r3, 3 + blr +22: subf r3, r3, r10 + addi r3, r3, 2 + blr +21: subf r3, r3, r10 + addi r3, r3, 1 + blr +19: addi r10, r10, (SZL - 1) +20: subf r3, r3, r10 + blr + +1: lbz r9, SZL(r10) + addi r10, r10, 1 + cmpwi cr1, r9, 0 + andi. r9, r10, (SZL - 1) + beq cr1, 19b + bne 1b + b 2b +EXPORT_SYMBOL(strlen) -- 2.13.3
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