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Subject[PATCH 4/5] x86_64, -march=native: REP STOSB support
Date
Use REP STOSB everywhere if CPU advertises fast REP STOSB.

Gcc LOVES to unroll memset(), using -mmemset-strategy saves terabytes of
.text.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
Makefile | 3 +++
arch/x86/boot/compressed/head_64.S | 4 ++++
arch/x86/crypto/sha1_ssse3_asm.S | 7 ++++++-
arch/x86/include/asm/page_64.h | 13 +++++++++++++
arch/x86/kernel/verify_cpu.S | 2 +-
arch/x86/lib/Makefile | 2 ++
arch/x86/lib/memset_64.S | 15 +++++++++++++++
arch/x86/lib/usercopy_64.c | 16 +++++++++++++++-
scripts/kconfig/cpuid.c | 6 +++++-
scripts/march-native.sh | 1 +
10 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index aa194c96d27c..31a6375d0e31 100644
--- a/Makefile
+++ b/Makefile
@@ -612,6 +612,9 @@ endif
ifdef CONFIG_MARCH_NATIVE_REP_MOVSB
KBUILD_CFLAGS += -mmemcpy-strategy=rep_byte:-1:align,rep_byte:-1:noalign
endif
+ifdef CONFIG_MARCH_NATIVE_REP_STOSB
+KBUILD_CFLAGS += -mmemset-strategy=rep_byte:-1:align,rep_byte:-1:noalign
+endif

ifeq ($(KBUILD_EXTMOD),)
# Objects we will link into vmlinux / subdirs we need to visit
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 6233ae35d0d9..a350d265e8af 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -520,8 +520,12 @@ relocated:
leaq _bss(%rip), %rdi
leaq _ebss(%rip), %rcx
subq %rdi, %rcx
+#ifdef CONFIG_MARCH_NATIVE_REP_STOSB
+ rep stosb
+#else
shrq $3, %rcx
rep stosq
+#endif

/*
* Do the extraction, and jump to the new kernel..
diff --git a/arch/x86/crypto/sha1_ssse3_asm.S b/arch/x86/crypto/sha1_ssse3_asm.S
index 99c5b8c4dc38..c98f8f2aead6 100644
--- a/arch/x86/crypto/sha1_ssse3_asm.S
+++ b/arch/x86/crypto/sha1_ssse3_asm.S
@@ -90,10 +90,15 @@
SHA1_PIPELINED_MAIN_BODY

# cleanup workspace
- mov $8, %ecx
mov %rsp, %rdi
xor %eax, %eax
+#ifdef CONFIG_MARCH_NATIVE_REP_STOSB
+ mov $64, %ecx
+ rep stosb
+#else
+ mov $8, %ecx
rep stosq
+#endif

mov %rbp, %rsp # deallocate workspace
pop %rbp
diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index 051da768273d..7654d5544e0b 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -40,6 +40,18 @@ extern unsigned long __phys_addr_symbol(unsigned long);
#define pfn_valid(pfn) ((pfn) < max_pfn)
#endif

+#ifdef CONFIG_MARCH_NATIVE_REP_STOSB
+static __always_inline void clear_page(void *page)
+{
+ uint32_t len = PAGE_SIZE;
+ asm volatile (
+ "rep stosb"
+ : "+D" (page), "+c" (len)
+ : "a" (0)
+ : "memory"
+ );
+}
+#else
void clear_page_orig(void *page);
void clear_page_rep(void *page);
void clear_page_erms(void *page);
@@ -53,6 +65,7 @@ static inline void clear_page(void *page)
"0" (page)
: "cc", "memory", "rax", "rcx");
}
+#endif

#ifdef CONFIG_MARCH_NATIVE_REP_MOVSB
static __always_inline void copy_page(void *to, void *from)
diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S
index 57b41dafc592..d3f3370e7dab 100644
--- a/arch/x86/kernel/verify_cpu.S
+++ b/arch/x86/kernel/verify_cpu.S
@@ -142,7 +142,7 @@ ENTRY(verify_cpu)
jnc .Lverify_cpu_no_longmode
#endif

-#ifdef CONFIG_MARCH_NATIVE_REP_MOVSB
+#if defined(CONFIG_MARCH_NATIVE_REP_MOVSB) || defined(CONFIG_MARCH_NATIVE_REP_STOSB)
xor %eax, %eax
cpuid
cmp $7, %eax
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index fa24cc717fb1..ed71e88cb859 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -59,7 +59,9 @@ endif
else
obj-y += iomap_copy_64.o
lib-y += csum-partial_64.o csum-copy_64.o csum-wrappers_64.o
+ifneq ($(CONFIG_MARCH_NATIVE_REP_STOSB),y)
lib-y += clear_page_64.o
+endif
ifneq ($(CONFIG_MARCH_NATIVE_REP_MOVSB),y)
lib-y += copy_page_64.o
endif
diff --git a/arch/x86/lib/memset_64.S b/arch/x86/lib/memset_64.S
index 9bc861c71e75..7786d1a65423 100644
--- a/arch/x86/lib/memset_64.S
+++ b/arch/x86/lib/memset_64.S
@@ -8,6 +8,20 @@

.weak memset

+#ifdef CONFIG_MARCH_NATIVE_REP_STOSB
+ENTRY(memset)
+ENTRY(__memset)
+ mov %esi, %eax
+ mov %rdi, %rsi
+ mov %rdx, %rcx
+ rep stosb
+ mov %rsi, %rax
+ ret
+ENDPROC(memset)
+ENDPROC(__memset)
+EXPORT_SYMBOL(memset)
+EXPORT_SYMBOL(__memset)
+#else
/*
* ISO C memset - set a memory block to a byte value. This function uses fast
* string to get better performance than the original function. The code is
@@ -140,3 +154,4 @@ ENTRY(memset_orig)
jmp .Lafter_bad_alignment
.Lfinal:
ENDPROC(memset_orig)
+#endif
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index fff28c6f73a2..a90779b12d89 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -16,11 +16,23 @@

unsigned long __clear_user(void __user *addr, unsigned long size)
{
- long __d0;
might_fault();
/* no memory constraint because it doesn't change any memory gcc knows
about */
stac();
+
+#ifdef CONFIG_MARCH_NATIVE_REP_STOSB
+ asm volatile (
+ "0: rep stosb\n"
+ "1:\n"
+ _ASM_EXTABLE(0b,1b)
+ : "+D" (addr), "+c" (size)
+ : "a" (0)
+ : "memory"
+ );
+#else
+ {
+ long __d0;
asm volatile(
" testq %[size8],%[size8]\n"
" jz 4f\n"
@@ -42,6 +54,8 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
_ASM_EXTABLE_UA(1b, 2b)
: [size8] "=&c"(size), [dst] "=&D" (__d0)
: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
+ }
+#endif
clac();
return size;
}
diff --git a/scripts/kconfig/cpuid.c b/scripts/kconfig/cpuid.c
index 2d78fba1dcc7..58d09bda61e5 100644
--- a/scripts/kconfig/cpuid.c
+++ b/scripts/kconfig/cpuid.c
@@ -45,6 +45,7 @@ static inline void cpuid2(uint32_t eax0, uint32_t ecx0, uint32_t *eax, uint32_t

static bool popcnt = false;
static bool rep_movsb = false;
+static bool rep_stosb = false;

static uint32_t eax0_max;

@@ -64,8 +65,10 @@ static void intel(void)
cpuid2(7, 0, &eax, &ecx, &edx, &ebx);
// printf("%08x %08x %08x %08x\n", eax, ecx, edx, ebx);

- if (ebx & (1 << 9))
+ if (ebx & (1 << 9)) {
rep_movsb = true;
+ rep_stosb = true;
+ }
}
}

@@ -88,6 +91,7 @@ int main(int argc, char *argv[])
#define _(x) if (streq(opt, #x)) return x ? EXIT_SUCCESS : EXIT_FAILURE
_(popcnt);
_(rep_movsb);
+ _(rep_stosb);
#undef _

return EXIT_FAILURE;
diff --git a/scripts/march-native.sh b/scripts/march-native.sh
index 87f00cdb8e10..a41a15a64df4 100755
--- a/scripts/march-native.sh
+++ b/scripts/march-native.sh
@@ -43,6 +43,7 @@ echo "-march=native: $COLLECT_GCC_OPTIONS"

"$CPUID" popcnt && option "CONFIG_MARCH_NATIVE_POPCNT"
"$CPUID" rep_movsb && option "CONFIG_MARCH_NATIVE_REP_MOVSB"
+"$CPUID" rep_stosb && option "CONFIG_MARCH_NATIVE_REP_STOSB"

for i in $COLLECT_GCC_OPTIONS; do
case $i in
--
2.21.0
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