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>
We'd like all architectures to convert to ARCH_ATOMIC, as once all
architectures are converted it will be possible to make significant
cleanups to the atomics headers, and this will make it much easier to
generically enable atomic functionality (e.g. debug logic in the
instrumented wrappers).
As a step towards that, this patch migrates csky to ARCH_ATOMIC. The
arch code provides arch_{atomic,atomic64,xchg,cmpxchg}*(), and common
code wraps these with optional instrumentation to provide the regular
functions.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Guo Ren <guoren@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210525140232.53872-17-mark.rutland@arm.com
Optimize the performance of cmpxchg by using more fine-grained
acquire/release barriers.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul E. McKenney <paulmck@kernel.org>
