| Message ID | 20160518165919.GA26903@flamenco |
|---|---|
| State | New |
| Headers | show |
On 18/05/2016 18:59, Emilio G. Cota wrote: > On Wed, May 18, 2016 at 17:09:48 +0200, Paolo Bonzini wrote: >> But honestly I think it would be even better to just use >> __sync_lock_test_and_set in the spinlock implementation and not add this >> to atomics.h. There's already enough issues with the current subset of >> atomics, I am not really happy to add non-SC read-modify-write >> operations to the mix. > > I can drop the two patches that touch atomic.h, and have the > spinlock patch as appended. Load acquire and store release are fine by me, I wanted to add them too. But the patch you attached is fine, I will salvage the load-acquire/store-release patch later. Thanks, Paolo > Thanks, > > Emilio > > commit 99c8f1049a1508edc9de30e3cf27898888aa7f68 > Author: Guillaume Delbergue <guillaume.delbergue@greensocs.com> > Date: Sun Oct 18 09:44:02 2015 +0200 > > qemu-thread: add simple test-and-set spinlock > > Signed-off-by: Guillaume Delbergue <guillaume.delbergue@greensocs.com> > [Rewritten. - Paolo] > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > [Emilio's additions: use TAS instead of atomic_xchg; emit acquire/release > barriers; call cpu_relax() while spinning; optimize for uncontended locks by > acquiring the lock with TAS instead of TATAS; add qemu_spin_locked().] > Signed-off-by: Emilio G. Cota <cota@braap.org> > > diff --git a/include/qemu/thread.h b/include/qemu/thread.h > index bdae6df..2d225ff 100644 > --- a/include/qemu/thread.h > +++ b/include/qemu/thread.h > @@ -1,6 +1,9 @@ > #ifndef __QEMU_THREAD_H > #define __QEMU_THREAD_H 1 > > +#include <errno.h> > +#include "qemu/processor.h" > +#include "qemu/atomic.h" > > typedef struct QemuMutex QemuMutex; > typedef struct QemuCond QemuCond; > @@ -60,4 +63,40 @@ struct Notifier; > void qemu_thread_atexit_add(struct Notifier *notifier); > void qemu_thread_atexit_remove(struct Notifier *notifier); > > +typedef struct QemuSpin { > + int value; > +} QemuSpin; > + > +static inline void qemu_spin_init(QemuSpin *spin) > +{ > + __sync_lock_release(&spin->value); > +} > + > +static inline void qemu_spin_lock(QemuSpin *spin) > +{ > + while (__sync_lock_test_and_set(&spin->value, true)) { > + while (atomic_read(&spin->value)) { > + cpu_relax(); > + } > + } > +} > + > +static inline int qemu_spin_trylock(QemuSpin *spin) > +{ > + if (__sync_lock_test_and_set(&spin->value, true)) { > + return -EBUSY; > + } > + return 0; > +} > + > +static inline bool qemu_spin_locked(QemuSpin *spin) > +{ > + return atomic_read(&spin->value); > +} > + > +static inline void qemu_spin_unlock(QemuSpin *spin) > +{ > + __sync_lock_release(&spin->value); > +} > + > #endif >
diff --git a/include/qemu/thread.h b/include/qemu/thread.h index bdae6df..2d225ff 100644 --- a/include/qemu/thread.h +++ b/include/qemu/thread.h @@ -1,6 +1,9 @@ #ifndef __QEMU_THREAD_H #define __QEMU_THREAD_H 1 +#include <errno.h> +#include "qemu/processor.h" +#include "qemu/atomic.h" typedef struct QemuMutex QemuMutex; typedef struct QemuCond QemuCond; @@ -60,4 +63,40 @@ struct Notifier; void qemu_thread_atexit_add(struct Notifier *notifier); void qemu_thread_atexit_remove(struct Notifier *notifier); +typedef struct QemuSpin { + int value; +} QemuSpin; + +static inline void qemu_spin_init(QemuSpin *spin) +{ + __sync_lock_release(&spin->value); +} + +static inline void qemu_spin_lock(QemuSpin *spin) +{ + while (__sync_lock_test_and_set(&spin->value, true)) { + while (atomic_read(&spin->value)) { + cpu_relax(); + } + } +} + +static inline int qemu_spin_trylock(QemuSpin *spin) +{ + if (__sync_lock_test_and_set(&spin->value, true)) { + return -EBUSY; + } + return 0; +} + +static inline bool qemu_spin_locked(QemuSpin *spin) +{ + return atomic_read(&spin->value); +} + +static inline void qemu_spin_unlock(QemuSpin *spin) +{ + __sync_lock_release(&spin->value); +} + #endif