| Message ID | 1463196873-17737-6-git-send-email-cota@braap.org |
|---|---|
| State | New |
| Headers | show |
On 14/05/2016 05:34, Emilio G. Cota wrote: > This new helper expands to __atomic_test_and_set with acquire semantics > where available; otherwise it expands to __sync_test_and_set, which > has acquire semantics. > > Signed-off-by: Emilio G. Cota <cota@braap.org> Non-seqcst read-modify-write operations are beyond what I expected to have in qemu/atomic.h, but I guess it's okay for test-and-set because of __sync_test_and_set. Paolo > --- > include/qemu/atomic.h | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h > index 5bc4d6c..6061a46 100644 > --- a/include/qemu/atomic.h > +++ b/include/qemu/atomic.h > @@ -113,6 +113,7 @@ > } while(0) > #endif > > +#define atomic_test_and_set_acquire(ptr) __atomic_test_and_set(ptr, __ATOMIC_ACQUIRE) > > /* All the remaining operations are fully sequentially consistent */ > > @@ -327,6 +328,8 @@ > #endif > #endif > > +#define atomic_test_and_set_acquire(ptr) __sync_lock_test_and_set(ptr, true) > + > /* Provide shorter names for GCC atomic builtins. */ > #define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1) > #define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1) >
On 14/05/16 06:34, Emilio G. Cota wrote: > This new helper expands to __atomic_test_and_set with acquire semantics > where available; otherwise it expands to __sync_test_and_set, which > has acquire semantics. Why don't also add atomic_clear_release() for completeness? Kind regards, Sergey > > Signed-off-by: Emilio G. Cota <cota@braap.org> > --- > include/qemu/atomic.h | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h > index 5bc4d6c..6061a46 100644 > --- a/include/qemu/atomic.h > +++ b/include/qemu/atomic.h > @@ -113,6 +113,7 @@ > } while(0) > #endif > > +#define atomic_test_and_set_acquire(ptr) __atomic_test_and_set(ptr, __ATOMIC_ACQUIRE) > > /* All the remaining operations are fully sequentially consistent */ > > @@ -327,6 +328,8 @@ > #endif > #endif > > +#define atomic_test_and_set_acquire(ptr) __sync_lock_test_and_set(ptr, true) > + > /* Provide shorter names for GCC atomic builtins. */ > #define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1) > #define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1)
On 17/05/2016 18:15, Sergey Fedorov wrote: > On 14/05/16 06:34, Emilio G. Cota wrote: >> This new helper expands to __atomic_test_and_set with acquire semantics >> where available; otherwise it expands to __sync_test_and_set, which >> has acquire semantics. > > Why don't also add atomic_clear_release() for completeness? The previous patch adds atomic_set_release. Paolo > Kind regards, > Sergey > >> >> Signed-off-by: Emilio G. Cota <cota@braap.org> >> --- >> include/qemu/atomic.h | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h >> index 5bc4d6c..6061a46 100644 >> --- a/include/qemu/atomic.h >> +++ b/include/qemu/atomic.h >> @@ -113,6 +113,7 @@ >> } while(0) >> #endif >> >> +#define atomic_test_and_set_acquire(ptr) __atomic_test_and_set(ptr, __ATOMIC_ACQUIRE) >> >> /* All the remaining operations are fully sequentially consistent */ >> >> @@ -327,6 +328,8 @@ >> #endif >> #endif >> >> +#define atomic_test_and_set_acquire(ptr) __sync_lock_test_and_set(ptr, true) >> + >> /* Provide shorter names for GCC atomic builtins. */ >> #define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1) >> #define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1) >
On 17/05/16 19:23, Paolo Bonzini wrote: > > On 17/05/2016 18:15, Sergey Fedorov wrote: >> On 14/05/16 06:34, Emilio G. Cota wrote: >>> This new helper expands to __atomic_test_and_set with acquire semantics >>> where available; otherwise it expands to __sync_test_and_set, which >>> has acquire semantics. >> Why don't also add atomic_clear_release() for completeness? > The previous patch adds atomic_set_release. Yes, but it would take the advantage of __sync_lock_release() being just a release barrier rather than a full barrier of smp_mb() in atomic_set_release(). But that's only the case for legacy __sync built-ins (before GCC 4.7.0), though. Kind regards, Sergey
On 17/05/2016 18:47, Sergey Fedorov wrote: >>> >> On 14/05/16 06:34, Emilio G. Cota wrote: >>>> >>> This new helper expands to __atomic_test_and_set with acquire semantics >>>> >>> where available; otherwise it expands to __sync_test_and_set, which >>>> >>> has acquire semantics. >>> >> Why don't also add atomic_clear_release() for completeness? >> > The previous patch adds atomic_set_release. > Yes, but it would take the advantage of __sync_lock_release() being just > a release barrier rather than a full barrier of smp_mb() in > atomic_set_release(). But that's only the case for legacy __sync > built-ins (before GCC 4.7.0), though. That will be fixed soon by adding smp_mb_acquire() and smp_mb_release(). :) Paolo
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h index 5bc4d6c..6061a46 100644 --- a/include/qemu/atomic.h +++ b/include/qemu/atomic.h @@ -113,6 +113,7 @@ } while(0) #endif +#define atomic_test_and_set_acquire(ptr) __atomic_test_and_set(ptr, __ATOMIC_ACQUIRE) /* All the remaining operations are fully sequentially consistent */ @@ -327,6 +328,8 @@ #endif #endif +#define atomic_test_and_set_acquire(ptr) __sync_lock_test_and_set(ptr, true) + /* Provide shorter names for GCC atomic builtins. */ #define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1) #define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1)
This new helper expands to __atomic_test_and_set with acquire semantics where available; otherwise it expands to __sync_test_and_set, which has acquire semantics. Signed-off-by: Emilio G. Cota <cota@braap.org> --- include/qemu/atomic.h | 3 +++ 1 file changed, 3 insertions(+)