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csky: atomic: Optimize cmpxchg with acquire & release 

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:

8e86f0b409 ("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
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
This commit is contained in:
Guo Ren 2022-04-06 20:30:13 +08:00
parent 8318f7c231
commit 186f69b64c
2 changed files with 67 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/csky/include/asm/barrier.h
View File

@ -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()

64
arch/csky/include/asm/cmpxchg.h
View File

@ -64,15 +64,71 @@ extern void __bad_xchg(void);
#define arch_cmpxchg_relaxed(ptr, o, n) \
(__cmpxchg_relaxed((ptr), (o), (n), sizeof(*(ptr))))
#define arch_cmpxchg(ptr, o, n) \
#define __cmpxchg_acquire(ptr, old, new, size) \
({ \
__typeof__(ptr) __ptr = (ptr); \
__typeof__(new) __new = (new); \
__typeof__(new) __tmp; \
__typeof__(old) __old = (old); \
__typeof__(*(ptr)) __ret; \
__smp_release_fence(); \
__ret = arch_cmpxchg_relaxed(ptr, o, n); \
__smp_acquire_fence(); \
switch (size) { \
case 4: \
asm volatile ( \
"1: ldex.w %0, (%3) \n" \
" cmpne %0, %4 \n" \
" bt 2f \n" \
" mov %1, %2 \n" \
" stex.w %1, (%3) \n" \
" bez %1, 1b \n" \
ACQUIRE_FENCE \
"2: \n" \
: "=&r" (__ret), "=&r" (__tmp) \
: "r" (__new), "r"(__ptr), "r"(__old) \
:); \
break; \
default: \
__bad_xchg(); \
} \
__ret; \
})
#define arch_cmpxchg_acquire(ptr, o, n) \
(__cmpxchg_acquire((ptr), (o), (n), sizeof(*(ptr))))
#define __cmpxchg(ptr, old, new, size) \
({ \
__typeof__(ptr) __ptr = (ptr); \
__typeof__(new) __new = (new); \
__typeof__(new) __tmp; \
__typeof__(old) __old = (old); \
__typeof__(*(ptr)) __ret; \
switch (size) { \
case 4: \
asm volatile ( \
RELEASE_FENCE \
"1: ldex.w %0, (%3) \n" \
" cmpne %0, %4 \n" \
" bt 2f \n" \
" mov %1, %2 \n" \
" stex.w %1, (%3) \n" \
" bez %1, 1b \n" \
FULL_FENCE \
"2: \n" \
: "=&r" (__ret), "=&r" (__tmp) \
: "r" (__new), "r"(__ptr), "r"(__old) \
:); \
break; \
default: \
__bad_xchg(); \
} \
__ret; \
})
#define arch_cmpxchg(ptr, o, n) \
(__cmpxchg((ptr), (o), (n), sizeof(*(ptr))))
#define arch_cmpxchg_local(ptr, o, n) \
(__cmpxchg_relaxed((ptr), (o), (n), sizeof(*(ptr))))
#else
#include <asm-generic/cmpxchg.h>
#endif