| Message ID | 1463196873-17737-7-git-send-email-cota@braap.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Emilio, On Fri, May 13, 2016 at 11:34 PM, Emilio G. Cota <cota@braap.org> wrote: > When __atomic is not available, we use full memory barriers instead > of smp/wmb, since acquire/release barriers apply to all memory > operations and not just to loads/stores, respectively. > If it is not too late can we rename this to atomic_load_acquire()/atomic_store_release() like in the linux kernel? Looks good either way. Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
On Sun, May 15, 2016 at 06:22:36 -0400, Pranith Kumar wrote: > On Fri, May 13, 2016 at 11:34 PM, Emilio G. Cota <cota@braap.org> wrote: > > When __atomic is not available, we use full memory barriers instead > > of smp/wmb, since acquire/release barriers apply to all memory > > operations and not just to loads/stores, respectively. > > If it is not too late can we rename this to > atomic_load_acquire()/atomic_store_release() like in the linux kernel? I'd keep read/set just for consistency with the rest of the file. BTW in the kernel, atomic_{read/set}_{acquire/release} are defined in include/linux/atomic.h: #ifndef atomic_read_acquire #define atomic_read_acquire(v) smp_load_acquire(&(v)->counter) #endif #ifndef atomic_set_release #define atomic_set_release(v, i) smp_store_release(&(v)->counter, (i)) #endif The smp_load/store variants are called much more frequently, though. Thanks, Emilio
On 14/05/16 06:34, Emilio G. Cota wrote: > When __atomic is not available, we use full memory barriers instead > of smp/wmb, since acquire/release barriers apply to all memory > operations and not just to loads/stores, respectively. > > Signed-off-by: Emilio G. Cota <cota@braap.org> > --- > include/qemu/atomic.h | 27 +++++++++++++++++++++++++++ > Update docs/atomics.txt? (The same for the previous patch.) Kind regards, Sergey
On 17/05/2016 18:53, Sergey Fedorov wrote: > On 14/05/16 06:34, Emilio G. Cota wrote: >> > When __atomic is not available, we use full memory barriers instead >> > of smp/wmb, since acquire/release barriers apply to all memory >> > operations and not just to loads/stores, respectively. >> > >> > Signed-off-by: Emilio G. Cota <cota@braap.org> >> > --- >> > include/qemu/atomic.h | 27 +++++++++++++++++++++++++++ >> > > Update docs/atomics.txt? (The same for the previous patch.) I'm okay with doing this separately. Paolo
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h index 6061a46..1766c22 100644 --- a/include/qemu/atomic.h +++ b/include/qemu/atomic.h @@ -56,6 +56,21 @@ __atomic_store(ptr, &_val, __ATOMIC_RELAXED); \ } while(0) +/* atomic read/set with acquire/release barrier */ +#define atomic_read_acquire(ptr) \ + ({ \ + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \ + typeof(*ptr) _val; \ + __atomic_load(ptr, &_val, __ATOMIC_ACQUIRE); \ + _val; \ + }) + +#define atomic_set_release(ptr, i) do { \ + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \ + typeof(*ptr) _val = (i); \ + __atomic_store(ptr, &_val, __ATOMIC_RELEASE); \ +} while(0) + /* Atomic RCU operations imply weak memory barriers */ #define atomic_rcu_read(ptr) \ @@ -243,6 +258,18 @@ #define atomic_read(ptr) (*(__typeof__(*ptr) volatile*) (ptr)) #define atomic_set(ptr, i) ((*(__typeof__(*ptr) volatile*) (ptr)) = (i)) +/* atomic read/set with acquire/release barrier */ +#define atomic_read_acquire(ptr) ({ \ + typeof(*ptr) _val = atomic_read(ptr); \ + smp_mb(); \ + _val; \ +}) + +#define atomic_set_release(ptr, i) do { \ + smp_mb(); \ + atomic_set(ptr, i); \ +} while (0) + /** * atomic_rcu_read - reads a RCU-protected pointer to a local variable * into a RCU read-side critical section. The pointer can later be safely
When __atomic is not available, we use full memory barriers instead of smp/wmb, since acquire/release barriers apply to all memory operations and not just to loads/stores, respectively. Signed-off-by: Emilio G. Cota <cota@braap.org> --- include/qemu/atomic.h | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+)