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csky: Optimize atomic_ops & cmpxchg

PATCH New [email protected] 1 participant 4 messages Apr 24, 2022

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v4 cover csky: Optimize atomic_ops & cmpxchg

From: Guo Ren <[email protected]>

Optimize arch_xchg|cmpxchg|cmpxchg_local with ASM acquire|release instructions instead of previous C based.

The generic atomic.h used cmpxchg to implement the atomic operations, it will cause daul loop to reduce the forward guarantee. The patch implement csky custom atomic operations with ldex/stex instructions for the best performance.

Changes in V4:
- Remove RELEASE_FENCE in ldex/stex loop by Buoqun's advice

Changes in V3:
- Add arch_atomic_(fetch_add_unless, inc_unless_negative, dec_unless_positive, dec_if_positive)

Changes in V2:
- Fixup use of acquire + release for barrier semantics by Rutland.

Guo Ren (3):
csky: atomic: Optimize cmpxchg with acquire & release
csky: atomic: Add custom atomic.h implementation
csky: atomic: Add conditional atomic operations' optimization

 arch/csky/include/asm/atomic.h  | 237 ++++++++++++++++++++++++++++++++
 arch/csky/include/asm/barrier.h |  11 +-
 arch/csky/include/asm/cmpxchg.h |  64 ++++++++-
 3 files changed, 304 insertions(+), 8 deletions(-)
 create mode 100644 arch/csky/include/asm/atomic.h
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2.25.1
author maintainer
#1 lore raw

PATCH v4 1/3 csky: atomic: Optimize cmpxchg with acquire & release

From: Guo Ren <[email protected]>

Optimize cmpxchg with ASM acquire/release fence ASM instructions instead of previous generic based. Prevent a fence when cmxchg's first load != old.

Comments by Rutland:

8e86f0b409a4 ("arm64: atomics: fix use of acquire + release for full barrier semantics")

Comments by Boqun:

FWIW, you probably need to make sure that a barrier instruction inside an lr/sc loop is a good thing. IIUC, the execution time of a barrier instruction is determined by the status of store buffers and invalidate queues (and probably other stuffs), so it may increase the execution time of the lr/sc loop, and make it unlikely to succeed. But this really depends on how the arch executes these instructions.

Link https://lore.kernel.org/linux-riscv/CAJF2gTSAxpAi=LbAdu7jntZRUa=-dJwL0VfmDfBV5MHB=rcZ-w@mail.gmail.com/T/#m27a0f1342995deae49ce1d0e1f2683f8a181d6c3 open here
Signed-off-by Guo Ren <[email protected]>
Signed-off-by Guo Ren <[email protected]>
Cc Mark Rutland <[email protected]>
---
 arch/csky/include/asm/barrier.h | 11 +++---
 arch/csky/include/asm/cmpxchg.h | 64 ++++++++++++++++++++++++++++++---
 2 files changed, 67 insertions(+), 8 deletions(-)
arch/csky/include/asm/barrier.h +7 -4
index f4045dd53e17..15de58b10aec 100644
@@ -37,17 +37,21 @@
  * bar.brar
  * bar.bwaw
  */
+#define FULL_FENCE		".long 0x842fc000\n"
+#define ACQUIRE_FENCE		".long 0x8427c000\n"
+#define RELEASE_FENCE		".long 0x842ec000\n"
+
 #define __bar_brw()	asm volatile (".long 0x842cc000\n":::"memory")
 #define __bar_br()	asm volatile (".long 0x8424c000\n":::"memory")
 #define __bar_bw()	asm volatile (".long 0x8428c000\n":::"memory")
 #define __bar_arw()	asm volatile (".long 0x8423c000\n":::"memory")
 #define __bar_ar()	asm volatile (".long 0x8421c000\n":::"memory")
 #define __bar_aw()	asm volatile (".long 0x8422c000\n":::"memory")
-#define __bar_brwarw()	asm volatile (".long 0x842fc000\n":::"memory")
-#define __bar_brarw()	asm volatile (".long 0x8427c000\n":::"memory")
+#define __bar_brwarw()	asm volatile (FULL_FENCE:::"memory")
+#define __bar_brarw()	asm volatile (ACQUIRE_FENCE:::"memory")
 #define __bar_bwarw()	asm volatile (".long 0x842bc000\n":::"memory")
 #define __bar_brwar()	asm volatile (".long 0x842dc000\n":::"memory")
-#define __bar_brwaw()	asm volatile (".long 0x842ec000\n":::"memory")
+#define __bar_brwaw()	asm volatile (RELEASE_FENCE:::"memory")
 #define __bar_brar()	asm volatile (".long 0x8425c000\n":::"memory")
 #define __bar_brar()	asm volatile (".long 0x8425c000\n":::"memory")
 #define __bar_bwaw()	asm volatile (".long 0x842ac000\n":::"memory")

@@ -56,7 +60,6 @@
 #define __smp_rmb()	__bar_brar()
 #define __smp_wmb()	__bar_bwaw()
 
-#define ACQUIRE_FENCE		".long 0x8427c000\n"
 #define __smp_acquire_fence()	__bar_brarw()
 #define __smp_release_fence()	__bar_brwaw()
arch/csky/include/asm/cmpxchg.h +60 -4

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2.25.1
author maintainer
#2 lore raw

PATCH v4 2/3 csky: atomic: Add custom atomic.h implementation

In reply to [email protected]

From: Guo Ren <[email protected]>

The generic atomic.h used cmpxchg to implement the atomic operations, it will cause daul loop to reduce the forward guarantee. The patch implement csky custom atomic operations with ldex/stex instructions for the best performance.

Important comment by Rutland:
8e86f0b409a4 ("arm64: atomics: fix use of acquire + release for full barrier semantics")

Link https://lore.kernel.org/linux-riscv/CAJF2gTSAxpAi=LbAdu7jntZRUa=-dJwL0VfmDfBV5MHB=rcZ-w@mail.gmail.com/T/#m27a0f1342995deae49ce1d0e1f2683f8a181d6c3 open here
Signed-off-by Guo Ren <[email protected]>
Signed-off-by Guo Ren <[email protected]>
Cc Mark Rutland <[email protected]>
---
 arch/csky/include/asm/atomic.h | 142 +++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)
 create mode 100644 arch/csky/include/asm/atomic.h
arch/csky/include/asm/atomic.h new file +142 -0
new file mode 100644
index 000000000000..56c9dc8e91b3
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_CSKY_ATOMIC_H
+#define __ASM_CSKY_ATOMIC_H
+
+#ifdef CONFIG_SMP
+#include <asm-generic/atomic64.h>
+
+#include <asm/cmpxchg.h>
+#include <asm/barrier.h>
+
+#define __atomic_acquire_fence()	__bar_brarw()
+
+#define __atomic_release_fence()	__bar_brwaw()
+
+static __always_inline int arch_atomic_read(const atomic_t *v)
+{
+	return READ_ONCE(v->counter);
+}
+static __always_inline void arch_atomic_set(atomic_t *v, int i)
+{
+	WRITE_ONCE(v->counter, i);
+}
+
+#define ATOMIC_OP(op)							\
+static __always_inline							\
+void arch_atomic_##op(int i, atomic_t *v)				\
+{									\
+	unsigned long tmp;						\
+	__asm__ __volatile__ (						\
+	"1:	ldex.w		%0, (%2)	\n"			\
+	"	" #op "		%0, %1		\n"			\
+	"	stex.w		%0, (%2)	\n"			\
+	"	bez		%0, 1b		\n"			\
+	: "=&r" (tmp)							\
+	: "r" (i), "r" (&v->counter)					\
+	: "memory");							\
+}
+
+ATOMIC_OP(add)
+ATOMIC_OP(sub)
+ATOMIC_OP(and)
+ATOMIC_OP( or)
+ATOMIC_OP(xor)
+
+#undef ATOMIC_OP
+
+#define ATOMIC_FETCH_OP(op)						\
+static __always_inline							\
+int arch_atomic_fetch_##op##_relaxed(int i, atomic_t *v)		\
+{									\
+	register int ret, tmp;						\
+	__asm__ __volatile__ (						\
+	"1:	ldex.w		%0, (%3) \n"				\
+	"	mov		%1, %0   \n"				\
+	"	" #op "		%0, %2   \n"				\
+	"	stex.w		%0, (%3) \n"				\
+	"	bez		%0, 1b   \n"				\
+		: "=&r" (tmp), "=&r" (ret)				\
+		: "r" (i), "r"(&v->counter) 				\
+		: "memory");						\
+	return ret;							\
+}
+
+#define ATOMIC_OP_RETURN(op, c_op)					\
+static __always_inline							\
+int arch_atomic_##op##_return_relaxed(int i, atomic_t *v)		\
+{									\
+	return arch_atomic_fetch_##op##_relaxed(i, v) c_op i;		\
+}
+
+#define ATOMIC_OPS(op, c_op)						\
+	ATOMIC_FETCH_OP(op)						\
+	ATOMIC_OP_RETURN(op, c_op)
+
+ATOMIC_OPS(add, +)
+ATOMIC_OPS(sub, -)
+
+#define arch_atomic_fetch_add_relaxed	arch_atomic_fetch_add_relaxed
+#define arch_atomic_fetch_sub_relaxed	arch_atomic_fetch_sub_relaxed
+
+#define arch_atomic_add_return_relaxed	arch_atomic_add_return_relaxed
+#define arch_atomic_sub_return_relaxed	arch_atomic_sub_return_relaxed
+
+#undef ATOMIC_OPS
+#undef ATOMIC_OP_RETURN
+
+#define ATOMIC_OPS(op)							\
+	ATOMIC_FETCH_OP(op)
+
+ATOMIC_OPS(and)
+ATOMIC_OPS( or)
+ATOMIC_OPS(xor)
+
+#define arch_atomic_fetch_and_relaxed	arch_atomic_fetch_and_relaxed
+#define arch_atomic_fetch_or_relaxed	arch_atomic_fetch_or_relaxed
+#define arch_atomic_fetch_xor_relaxed	arch_atomic_fetch_xor_relaxed
+
+#undef ATOMIC_OPS
+
+#undef ATOMIC_FETCH_OP
+
+#define ATOMIC_OP()							\
+static __always_inline							\
+int arch_atomic_xchg_relaxed(atomic_t *v, int n)			\
+{									\
+	return __xchg_relaxed(n, &(v->counter), 4);			\
+}									\
+static __always_inline							\
+int arch_atomic_cmpxchg_relaxed(atomic_t *v, int o, int n)		\
+{									\
+	return __cmpxchg_relaxed(&(v->counter), o, n, 4);		\
+}									\
+static __always_inline							\
+int arch_atomic_cmpxchg_acquire(atomic_t *v, int o, int n)		\
+{									\
+	return __cmpxchg_acquire(&(v->counter), o, n, 4);		\
+}									\
+static __always_inline							\
+int arch_atomic_cmpxchg(atomic_t *v, int o, int n)			\
+{									\
+	return __cmpxchg(&(v->counter), o, n, 4);			\
+}
+
+#define ATOMIC_OPS()							\
+	ATOMIC_OP()
+
+ATOMIC_OPS()
+
+#define arch_atomic_xchg_relaxed	arch_atomic_xchg_relaxed
+#define arch_atomic_cmpxchg_relaxed	arch_atomic_cmpxchg_relaxed
+#define arch_atomic_cmpxchg_acquire	arch_atomic_cmpxchg_acquire
+#define arch_atomic_cmpxchg		arch_atomic_cmpxchg
+
+#undef ATOMIC_OPS
+#undef ATOMIC_OP
+
+#else
+#include <asm-generic/atomic.h>
+#endif
+
+#endif /* __ASM_CSKY_ATOMIC_H */
Signature · 1 line
2.25.1
author maintainer
#3 lore raw

PATCH v4 3/3 csky: atomic: Add conditional atomic operations' optimization

In reply to [email protected]

From: Guo Ren <[email protected]>

Add conditional atomic operations' optimization:
- arch_atomic_fetch_add_unless
- arch_atomic_inc_unless_negative
- arch_atomic_dec_unless_positive
- arch_atomic_dec_if_positive

Comments by Boqun:

FWIW, you probably need to make sure that a barrier instruction inside an lr/sc loop is a good thing. IIUC, the execution time of a barrier instruction is determined by the status of store buffers and invalidate queues (and probably other stuffs), so it may increase the execution time of the lr/sc loop, and make it unlikely to succeed. But this really depends on how the arch executes these instructions.

Signed-off-by Guo Ren <[email protected]>
Signed-off-by Guo Ren <[email protected]>
Cc Boqun Feng <[email protected]>
---
 arch/csky/include/asm/atomic.h | 95 ++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
arch/csky/include/asm/atomic.h +95 -0
index 56c9dc8e91b3..60406ef9c2bb 100644
@@ -100,6 +100,101 @@ ATOMIC_OPS(xor)
 
 #undef ATOMIC_FETCH_OP
 
+static __always_inline int
+arch_atomic_fetch_add_unless(atomic_t *v, int a, int u)
+{
+	int prev, tmp;
+
+	__asm__ __volatile__ (
+		RELEASE_FENCE
+		"1:	ldex.w		%0, (%3)	\n"
+		"	cmpne		%0, %4		\n"
+		"	bf		2f		\n"
+		"	mov		%1, %0		\n"
+		"	add		%1, %2		\n"
+		"	stex.w		%1, (%3)	\n"
+		"	bez		%1, 1b		\n"
+		FULL_FENCE
+		"2:\n"
+		: "=&r" (prev), "=&r" (tmp)
+		: "r" (a), "r" (&v->counter), "r" (u)
+		: "memory");
+
+	return prev;
+}
+#define arch_atomic_fetch_add_unless arch_atomic_fetch_add_unless
+
+static __always_inline bool
+arch_atomic_inc_unless_negative(atomic_t *v)
+{
+	int rc, tmp;
+
+	__asm__ __volatile__ (
+		RELEASE_FENCE
+		"1:	ldex.w		%0, (%2)	\n"
+		"	movi		%1, 0		\n"
+		"	blz		%0, 2f		\n"
+		"	movi		%1, 1		\n"
+		"	addi		%0, 1		\n"
+		"	stex.w		%0, (%2)	\n"
+		"	bez		%0, 1b		\n"
+		FULL_FENCE
+		"2:\n"
+		: "=&r" (tmp), "=&r" (rc)
+		: "r" (&v->counter)
+		: "memory");
+
+	return tmp ? true : false;
+
+}
+#define arch_atomic_inc_unless_negative arch_atomic_inc_unless_negative
+
+static __always_inline bool
+arch_atomic_dec_unless_positive(atomic_t *v)
+{
+	int rc, tmp;
+
+	__asm__ __volatile__ (
+		RELEASE_FENCE
+		"1:	ldex.w		%0, (%2)	\n"
+		"	movi		%1, 0		\n"
+		"	bhz		%0, 2f		\n"
+		"	movi		%1, 1		\n"
+		"	subi		%0, 1		\n"
+		"	stex.w		%0, (%2)	\n"
+		"	bez		%0, 1b		\n"
+		FULL_FENCE
+		"2:\n"
+		: "=&r" (tmp), "=&r" (rc)
+		: "r" (&v->counter)
+		: "memory");
+
+	return tmp ? true : false;
+}
+#define arch_atomic_dec_unless_positive arch_atomic_dec_unless_positive
+
+static __always_inline int
+arch_atomic_dec_if_positive(atomic_t *v)
+{
+	int dec, tmp;
+
+	__asm__ __volatile__ (
+		RELEASE_FENCE
+		"1:	ldex.w		%0, (%2)	\n"
+		"	subi		%1, %0, 1	\n"
+		"	blz		%1, 2f		\n"
+		"	stex.w		%1, (%2)	\n"
+		"	bez		%1, 1b		\n"
+		FULL_FENCE
+		"2:\n"
+		: "=&r" (dec), "=&r" (tmp)
+		: "r" (&v->counter)
+		: "memory");
+
+	return dec - 1;
+}
+#define arch_atomic_dec_if_positive arch_atomic_dec_if_positive
+
 #define ATOMIC_OP()							\
 static __always_inline							\
 int arch_atomic_xchg_relaxed(atomic_t *v, int n)			\
Signature · 1 line
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