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| author |   Peter Zijlstra <peterz@infradead.org> | 2016-06-01 19:23:54 +0200 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2016-06-14 11:55:14 +0200 |
| commit | 7cb45c0fe9858f92cc264f6bf9d2f6a0e7d3b249 (patch) | |
| tree | f429581d6b993e303a297a461d06cd0dad58ea68 /include/asm-generic/barrier.h | |
| parent | locking/barriers: Introduce smp_acquire__after_ctrl_dep() (diff) | |
| download | linux-dev-7cb45c0fe9858f92cc264f6bf9d2f6a0e7d3b249.tar.xz linux-dev-7cb45c0fe9858f92cc264f6bf9d2f6a0e7d3b249.zip | |
locking/barriers: Move smp_cond_load_acquire() to asm-generic/barrier.h
Since all asm/barrier.h should/must include asm-generic/barrier.h the
latter is a good place for generic infrastructure like this.
This also allows archs to override the new smp_acquire__after_ctrl_dep().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/asm-generic/barrier.h')
| -rw-r--r-- | include/asm-generic/barrier.h | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index 1cceca146905..ab7b0bd7d4dd 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -207,5 +207,44 @@ do { \ #define virt_store_release(p, v) __smp_store_release(p, v) #define virt_load_acquire(p) __smp_load_acquire(p) +/** + * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency + * + * A control dependency provides a LOAD->STORE order, the additional RMB + * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order, + * aka. (load)-ACQUIRE. + * + * Architectures that do not do load speculation can have this be barrier(). + */ +#ifndef smp_acquire__after_ctrl_dep +#define smp_acquire__after_ctrl_dep() smp_rmb() +#endif + +/** + * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering + * @ptr: pointer to the variable to wait on + * @cond: boolean expression to wait for + * + * Equivalent to using smp_load_acquire() on the condition variable but employs + * the control dependency of the wait to reduce the barrier on many platforms. + * + * Due to C lacking lambda expressions we load the value of *ptr into a + * pre-named variable @VAL to be used in @cond. + */ +#ifndef smp_cond_load_acquire +#define smp_cond_load_acquire(ptr, cond_expr) ({ \ + typeof(ptr) __PTR = (ptr); \ + typeof(*ptr) VAL; \ + for (;;) { \ + VAL = READ_ONCE(*__PTR); \ + if (cond_expr) \ + break; \ + cpu_relax(); \ + } \ + smp_acquire__after_ctrl_dep(); \ + VAL; \ +}) +#endif + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_GENERIC_BARRIER_H */ |