Subject: [PATCH v2] powerpc: memcpy optimization for 64bit LE

From: Philippe Bergheaud <[email-masked]>
Date: Thu, 07 Nov 2013 14:01:29 +0100

Unaligned stores take alignment exceptions on POWER7 running in little-endian.
This is a dumb little-endian base memcpy that prevents unaligned stores.
Once booted the feature fixup code switches over to the VMX copy loops
(which are already endian safe).

The question is what we do before that switch over. The base 64bit
memcpy takes alignment exceptions on POWER7 so we can't use it as is.
Fixing the causes of alignment exception would slow it down, because
we'd need to ensure all loads and stores are aligned either through
rotate tricks or bytewise loads and stores. Either would be bad for
all other 64bit platforms.

Signed-off-by: Philippe Bergheaud <[email-masked]>
---
  arch/powerpc/include/asm/string.h |    4 ----
  arch/powerpc/kernel/ppc_ksyms.c   |    2 --
  arch/powerpc/lib/Makefile         |    2 --
  arch/powerpc/lib/memcpy_64.S      |   19 +++++++++++++++++++
  4 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h
index 0dffad6..e40010a 100644
--- a/arch/powerpc/include/asm/string.h
+++ b/arch/powerpc/include/asm/string.h
@@ -10,9 +10,7 @@
  #define __HAVE_ARCH_STRNCMP
  #define __HAVE_ARCH_STRCAT
  #define __HAVE_ARCH_MEMSET
-#ifdef __BIG_ENDIAN__
  #define __HAVE_ARCH_MEMCPY
-#endif
  #define __HAVE_ARCH_MEMMOVE
  #define __HAVE_ARCH_MEMCMP
  #define __HAVE_ARCH_MEMCHR
@@ -24,9 +22,7 @@ extern int strcmp(const char *,const char *);
  extern int strncmp(const char *, const char *, __kernel_size_t);
  extern char * strcat(char *, const char *);
  extern void * memset(void *,int,__kernel_size_t);
-#ifdef __BIG_ENDIAN__
  extern void * memcpy(void *,const void *,__kernel_size_t);
-#endif
  extern void * memmove(void *,const void *,__kernel_size_t);
  extern int memcmp(const void *,const void *,__kernel_size_t);
  extern void * memchr(const void *,int,__kernel_size_t);
diff --git a/arch/powerpc/kernel/ppc_ksyms.c b/arch/powerpc/kernel/ppc_ksyms.c
index 526ad5c..0c2dd60 100644
--- a/arch/powerpc/kernel/ppc_ksyms.c
+++ b/arch/powerpc/kernel/ppc_ksyms.c
@@ -147,9 +147,7 @@ EXPORT_SYMBOL(__ucmpdi2);
  #endif
  long long __bswapdi2(long long);
  EXPORT_SYMBOL(__bswapdi2);
-#ifdef __BIG_ENDIAN__
  EXPORT_SYMBOL(memcpy);
-#endif
  EXPORT_SYMBOL(memset);
  EXPORT_SYMBOL(memmove);
  EXPORT_SYMBOL(memcmp);
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 5310132..6670361 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -23,9 +23,7 @@ obj-y			+= checksum_$(CONFIG_WORD_SIZE).o
  obj-$(CONFIG_PPC64)	+= checksum_wrappers_64.o
  endif

-ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),)
  obj-$(CONFIG_PPC64)		+= memcpy_power7.o memcpy_64.o
-endif

  obj-$(CONFIG_PPC_EMULATE_SSTEP)	+= sstep.o ldstfp.o

diff --git a/arch/powerpc/lib/memcpy_64.S b/arch/powerpc/lib/memcpy_64.S
index d2bbbc8..358cf74 100644
--- a/arch/powerpc/lib/memcpy_64.S
+++ b/arch/powerpc/lib/memcpy_64.S
@@ -12,10 +12,28 @@
  	.align	7
  _GLOBAL(memcpy)
  BEGIN_FTR_SECTION
+#ifdef __LITTLE_ENDIAN__
+	cmpdi cr7,r5,0		/* dumb little-endian memcpy */
+#else
  	std	r3,48(r1)	/* save destination pointer for return value */
+#endif
  FTR_SECTION_ELSE
  	b	memcpy_power7
  ALT_FTR_SECTION_END_IFCLR(CPU_FTR_VMX_COPY)
+#ifdef __LITTLE_ENDIAN__
+	addi r5,r5,-1
+	addi r9,r3,-1
+	add r5,r3,r5
+	subf r5,r9,r5
+	addi r4,r4,-1
+	mtctr r5
+	beqlr cr7
+1:
+	lbzu r10,1(r4)
+	stbu r10,1(r9)
+	bdnz 1b
+	blr
+#else
  	PPC_MTOCRF(0x01,r5)
  	cmpldi	cr1,r5,16
  	neg	r6,r3		# LS 3 bits = # bytes to 8-byte dest bdry
@@ -201,3 +219,4 @@ END_FTR_SECTION_IFCLR(CPU_FTR_UNALIGNED_LD_STD)
  	stb	r0,0(r3)
  4:	ld	r3,48(r1)	/* return dest pointer */
  	blr
+#endif
-- 1.7.10.4