From: Borislav Petkov <borislav.petkov@xxxxxxx>
Date: Fri, 5 Mar 2010 17:34:46 +0100
Subject: [PATCH 2/2] x86: Add optimized popcnt variants
Add support for the hardware version of the Hamming weight function,
popcnt, present in CPUs which advertize it under CPUID, Function
0x0000_0001_ECX[23]. On CPUs which don't support it, we fallback to the
default lib/hweight.c sw versions.
A synthetic benchmark comparing popcnt with __sw_hweight64 showed almost
a 3x speedup on a F10h machine.
Signed-off-by: Borislav Petkov <borislav.petkov@xxxxxxx>
---
arch/x86/Kconfig | 5 ++
arch/x86/include/asm/alternative.h | 9 +++-
arch/x86/include/asm/arch_hweight.h | 59 +++++++++++++++++++++++++++++
arch/x86/include/asm/bitops.h | 4 +-
include/asm-generic/bitops/arch_hweight.h | 22 +++++++++--
lib/Makefile | 3 +
lib/hweight.c | 20 +++++-----
scripts/Makefile.lib | 4 ++
8 files changed, 108 insertions(+), 18 deletions(-)
create mode 100644 arch/x86/include/asm/arch_hweight.h
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0eacb1f..89d8c54 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -238,6 +238,11 @@ config X86_32_LAZY_GS
def_bool y
depends on X86_32 && !CC_STACKPROTECTOR
+config ARCH_HWEIGHT_CFLAGS
+ string
+ default "-fcall-saved-ecx -fcall-saved-edx" if X86_32
+ default "-fcall-saved-rdi -fcall-saved-rsi -fcall-saved-rdx -fcall-saved-rcx -fcall-saved-r8 -fcall-saved-r9 -fcall-saved-r10 -fcall-saved-r11" if X86_64
+
config KTIME_SCALAR
def_bool X86_32
source "init/Kconfig"
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index b09ec55..67dae51 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -39,9 +39,6 @@
#define LOCK_PREFIX ""
#endif
-/* This must be included *after* the definition of LOCK_PREFIX */
-#include <asm/cpufeature.h>
-
struct alt_instr {
u8 *instr; /* original instruction */
u8 *replacement;
@@ -96,6 +93,12 @@ static inline int alternatives_text_reserved(void *start, void *end)
".previous"
/*
+ * This must be included *after* the definition of ALTERNATIVE due to
+ * <asm/arch_hweight.h>
+ */
+#include <asm/cpufeature.h>
+
+/*
* Alternative instructions for different CPU types or capabilities.
*
* This allows to use optimized instructions even on generic binary
diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
new file mode 100644
index 0000000..d1fc3c2
--- /dev/null
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -0,0 +1,59 @@
+#ifndef _ASM_X86_HWEIGHT_H
+#define _ASM_X86_HWEIGHT_H
+
+#ifdef CONFIG_64BIT
+/* popcnt %rdi, %rax */
+#define POPCNT ".byte 0xf3,0x48,0x0f,0xb8,0xc7"
+#define REG_IN "D"
+#define REG_OUT "a"
+#else
+/* popcnt %eax, %eax */
+#define POPCNT ".byte 0xf3,0x0f,0xb8,0xc0"
+#define REG_IN "a"
+#define REG_OUT "a"
+#endif
+
+/*
+ * __sw_hweightXX are called from within the alternatives below
+ * and callee-clobbered registers need to be taken care of. See
+ * ARCH_HWEIGHT_CFLAGS in <arch/x86/Kconfig> for the respective
+ * compiler switches.
+ */
+static inline unsigned int __arch_hweight32(unsigned int w)
+{
+ unsigned int res = 0;
+
+ asm (ALTERNATIVE("call __sw_hweight32", POPCNT, X86_FEATURE_POPCNT)
+ : "="REG_OUT (res)
+ : REG_IN (w));
+
+ return res;
+}
+
+static inline unsigned int __arch_hweight16(unsigned int w)
+{
+ return __arch_hweight32(w & 0xffff);
+}
+
+static inline unsigned int __arch_hweight8(unsigned int w)
+{
+ return __arch_hweight32(w & 0xff);
+}
+
+static inline unsigned long __arch_hweight64(__u64 w)
+{
+ unsigned long res = 0;
+
+#ifdef CONFIG_X86_32
+ return __arch_hweight32((u32)w) +
+ __arch_hweight32((u32)(w >> 32));
+#else
+ asm (ALTERNATIVE("call __sw_hweight64", POPCNT, X86_FEATURE_POPCNT)
+ : "="REG_OUT (res)
+ : REG_IN (w));
+#endif /* CONFIG_X86_32 */
+
+ return res;
+}
+
+#endif
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 02b47a6..545776e 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -444,7 +444,9 @@ static inline int fls(int x)
#define ARCH_HAS_FAST_MULTIPLIER 1
-#include <asm-generic/bitops/hweight.h>
+#include <asm/arch_hweight.h>
+
+#include <asm-generic/bitops/const_hweight.h>
#endif /* __KERNEL__ */
diff --git a/include/asm-generic/bitops/arch_hweight.h b/include/asm-generic/bitops/arch_hweight.h
index 3a7be84..9a81c1e 100644
--- a/include/asm-generic/bitops/arch_hweight.h
+++ b/include/asm-generic/bitops/arch_hweight.h
@@ -3,9 +3,23 @@
#include <asm/types.h>
-extern unsigned int __arch_hweight32(unsigned int w);
-extern unsigned int __arch_hweight16(unsigned int w);
-extern unsigned int __arch_hweight8(unsigned int w);
-extern unsigned long __arch_hweight64(__u64 w);
+inline unsigned int __arch_hweight32(unsigned int w)
+{
+ return __sw_hweight32(w);
+}
+inline unsigned int __arch_hweight16(unsigned int w)
+{
+ return __sw_hweight16(w);
+}
+
+inline unsigned int __arch_hweight8(unsigned int w)
+{
+ return __sw_hweight8(w);
+}
+
+inline unsigned long __arch_hweight64(__u64 w)
+{
+ return __sw_hweight64(w);
+}
#endif /* _ASM_GENERIC_BITOPS_HWEIGHT_H_ */
diff --git a/lib/Makefile b/lib/Makefile
index 2e152ae..abe63a8 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -39,7 +39,10 @@ lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
lib-$(CONFIG_GENERIC_FIND_FIRST_BIT) += find_next_bit.o
lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
obj-$(CONFIG_GENERIC_FIND_LAST_BIT) += find_last_bit.o
+
+CFLAGS_hweight.o = $(subst $(quote),,$(CONFIG_ARCH_HWEIGHT_CFLAGS))
obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
+
obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
obj-$(CONFIG_BTREE) += btree.o
obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
diff --git a/lib/hweight.c b/lib/hweight.c
index a6927e7..3c79d50 100644
--- a/lib/hweight.c
+++ b/lib/hweight.c
@@ -9,7 +9,7 @@
* The Hamming Weight of a number is the total number of bits set in it.
*/
-unsigned int __arch_hweight32(unsigned int w)
+unsigned int __sw_hweight32(unsigned int w)
{
#ifdef ARCH_HAS_FAST_MULTIPLIER
w -= (w >> 1) & 0x55555555;
@@ -24,30 +24,30 @@ unsigned int __arch_hweight32(unsigned int w)
return (res + (res >> 16)) & 0x000000FF;
#endif
}
-EXPORT_SYMBOL(__arch_hweight32);
+EXPORT_SYMBOL(__sw_hweight32);
-unsigned int __arch_hweight16(unsigned int w)
+unsigned int __sw_hweight16(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x5555);
res = (res & 0x3333) + ((res >> 2) & 0x3333);
res = (res + (res >> 4)) & 0x0F0F;
return (res + (res >> 8)) & 0x00FF;
}
-EXPORT_SYMBOL(__arch_hweight16);
+EXPORT_SYMBOL(__sw_hweight16);
-unsigned int __arch_hweight8(unsigned int w)
+unsigned int __sw_hweight8(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x55);
res = (res & 0x33) + ((res >> 2) & 0x33);
return (res + (res >> 4)) & 0x0F;
}
-EXPORT_SYMBOL(__arch_hweight8);
+EXPORT_SYMBOL(__sw_hweight8);
-unsigned long __arch_hweight64(__u64 w)
+unsigned long __sw_hweight64(__u64 w)
{
#if BITS_PER_LONG == 32
- return __arch_hweight32((unsigned int)(w >> 32)) +
- __arch_hweight32((unsigned int)w);
+ return __sw_hweight32((unsigned int)(w >> 32)) +
+ __sw_hweight32((unsigned int)w);
#elif BITS_PER_LONG == 64
#ifdef ARCH_HAS_FAST_MULTIPLIER
w -= (w >> 1) & 0x5555555555555555ul;
@@ -64,4 +64,4 @@ unsigned long __arch_hweight64(__u64 w)
#endif
#endif
}
-EXPORT_SYMBOL(__arch_hweight64);
+EXPORT_SYMBOL(__sw_hweight64);
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index f9bdf26..cbcd654 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -245,3 +245,7 @@ quiet_cmd_lzo = LZO $@
cmd_lzo = (cat $(filter-out FORCE,$^) | \
lzop -9 && $(call size_append, $(filter-out FORCE,$^))) > $@ || \
(rm -f $@ ; false)
+
+# misc stuff
+# ---------------------------------------------------------------------------
+quote:="
--
1.7.0.2
--
Regards/Gruss,
Boris.
--
Advanced Micro Devices, Inc.
Operating Systems Research Center
--
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