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Subject[PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions
Date
If we're running on a v7 ARM CPU, detect if the CPU supports the
sdiv/udiv instructions and replace the signed and unsigned
division library functions with an sdiv/udiv instruction.

Running the perf messaging benchmark in pipe mode

$ perf bench sched messaging -p

shows a modest improvement on my v7 CPU.

before:
(5.060 + 5.960 + 5.971 + 5.643 + 6.029 + 5.665 + 6.050 + 5.870 + 6.117 + 5.683) / 10 = 5.805

after:
(4.884 + 5.549 + 5.749 + 6.001 + 5.460 + 5.103 + 5.956 + 6.112 + 5.468 + 5.093) / 10 = 5.538

(5.805 - 5.538) / 5.805 = 4.6%

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---

Changes since v1:
* Replace signed with unsigned in unsigned divide function
* drop & in inline assembly
* Use IS_ENABLED() instead of #ifdef
* Pass DIV_V7 into lib1funcs.S instead of depending on ZIMAGE or CPU_V7

arch/arm/kernel/setup.c | 13 ++++++++++-
arch/arm/lib/Makefile | 6 +++++
arch/arm/lib/div-v7.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++
arch/arm/lib/lib1funcs.S | 16 +++++++++++++
4 files changed, 92 insertions(+), 1 deletion(-)
create mode 100644 arch/arm/lib/div-v7.c

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 0e1e2b3..f9e577a 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -30,6 +30,7 @@
#include <linux/bug.h>
#include <linux/compiler.h>
#include <linux/sort.h>
+#include <linux/static_key.h>

#include <asm/unified.h>
#include <asm/cp15.h>
@@ -365,9 +366,11 @@ void __init early_print(const char *str, ...)
printk("%s", buf);
}

+struct static_key cpu_has_idiv = STATIC_KEY_INIT_FALSE;
+
static void __init cpuid_init_hwcaps(void)
{
- unsigned int divide_instrs, vmsa;
+ unsigned int divide_instrs, vmsa, idiv_mask;

if (cpu_architecture() < CPU_ARCH_ARMv7)
return;
@@ -381,6 +384,14 @@ static void __init cpuid_init_hwcaps(void)
elf_hwcap |= HWCAP_IDIVT;
}

+ if (IS_ENABLED(CONFIG_THUMB2_KERNEL))
+ idiv_mask = HWCAP_IDIVT;
+ else
+ idiv_mask = HWCAP_IDIVA;
+
+ if (elf_hwcap & idiv_mask)
+ static_key_slow_inc(&cpu_has_idiv);
+
/* LPAE implies atomic ldrd/strd instructions */
vmsa = (read_cpuid_ext(CPUID_EXT_MMFR0) & 0xf) >> 0;
if (vmsa >= 5)
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index bd454b0..38621729 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -15,6 +15,12 @@ lib-y := backtrace.o changebit.o csumipv6.o csumpartial.o \
io-readsb.o io-writesb.o io-readsl.o io-writesl.o \
call_with_stack.o

+lib-$(CONFIG_CPU_V7) += div-v7.o
+CFLAGS_div-v7.o := -march=armv7-a
+ifeq ($(CONFIG_CPU_V7),y)
+ AFLAGS_lib1funcs.o := -DDIV_V7
+endif
+
mmu-y := clear_user.o copy_page.o getuser.o putuser.o

# the code in uaccess.S is not preemption safe and
diff --git a/arch/arm/lib/div-v7.c b/arch/arm/lib/div-v7.c
new file mode 100644
index 0000000..e20945a
--- /dev/null
+++ b/arch/arm/lib/div-v7.c
@@ -0,0 +1,58 @@
+/* Copyright (c) 2013, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/static_key.h>
+
+extern int ___aeabi_idiv(int, int);
+extern unsigned ___aeabi_uidiv(int, int);
+
+extern struct static_key cpu_has_idiv;
+
+int __aeabi_idiv(int numerator, int denominator)
+{
+ if (static_key_false(&cpu_has_idiv)) {
+ int ret;
+
+ asm volatile (
+ ".arch_extension idiv\n"
+ "sdiv %0, %1, %2"
+ : "=r" (ret)
+ : "r" (numerator), "r" (denominator));
+
+ return ret;
+ }
+
+ return ___aeabi_idiv(numerator, denominator);
+}
+
+int __divsi3(int numerator, int denominator)
+ __attribute__((alias("__aeabi_idiv")));
+
+unsigned __aeabi_uidiv(unsigned numerator, unsigned denominator)
+{
+ if (static_key_false(&cpu_has_idiv)) {
+ unsigned ret;
+
+ asm volatile (
+ ".arch_extension idiv\n"
+ "udiv %0, %1, %2"
+ : "=r" (ret)
+ : "r" (numerator), "r" (denominator));
+
+ return ret;
+ }
+
+ return ___aeabi_uidiv(numerator, denominator);
+}
+
+unsigned __udivsi3(unsigned numerator, unsigned denominator)
+ __attribute__((alias("__aeabi_uidiv")));
diff --git a/arch/arm/lib/lib1funcs.S b/arch/arm/lib/lib1funcs.S
index c562f64..82bbcc7 100644
--- a/arch/arm/lib/lib1funcs.S
+++ b/arch/arm/lib/lib1funcs.S
@@ -205,8 +205,12 @@ Boston, MA 02111-1307, USA. */
.endm


+#ifdef DIV_V7
+ENTRY(___aeabi_uidiv)
+#else
ENTRY(__udivsi3)
ENTRY(__aeabi_uidiv)
+#endif
UNWIND(.fnstart)

subs r2, r1, #1
@@ -232,8 +236,12 @@ UNWIND(.fnstart)
mov pc, lr

UNWIND(.fnend)
+#ifdef DIV_V7
+ENDPROC(___aeabi_uidiv)
+#else
ENDPROC(__udivsi3)
ENDPROC(__aeabi_uidiv)
+#endif

ENTRY(__umodsi3)
UNWIND(.fnstart)
@@ -253,8 +261,12 @@ UNWIND(.fnstart)
UNWIND(.fnend)
ENDPROC(__umodsi3)

+#ifdef DIV_V7
+ENTRY(___aeabi_idiv)
+#else
ENTRY(__divsi3)
ENTRY(__aeabi_idiv)
+#endif
UNWIND(.fnstart)

cmp r1, #0
@@ -293,8 +305,12 @@ UNWIND(.fnstart)
mov pc, lr

UNWIND(.fnend)
+#ifdef DIV_V7
+ENDPROC(___aeabi_idiv)
+#else
ENDPROC(__divsi3)
ENDPROC(__aeabi_idiv)
+#endif

ENTRY(__modsi3)
UNWIND(.fnstart)
--
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