On Thu, Apr 14, 2016 at 12:13:38AM -0700, Jason Low wrote: > Use WFE to avoid most spinning with MCS spinlocks. This is implemented > with the new cmpwait() mechanism for comparing and waiting for the MCS > locked value to change using LDXR + WFE. > > Signed-off-by: Jason Low <[email protected]> > --- > arch/arm64/include/asm/mcs_spinlock.h | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > create mode 100644 arch/arm64/include/asm/mcs_spinlock.h > > diff --git a/arch/arm64/include/asm/mcs_spinlock.h > b/arch/arm64/include/asm/mcs_spinlock.h > new file mode 100644 > index 0000000..d295d9d > --- /dev/null > +++ b/arch/arm64/include/asm/mcs_spinlock.h > @@ -0,0 +1,21 @@ > +#ifndef __ASM_MCS_SPINLOCK_H > +#define __ASM_MCS_SPINLOCK_H > + > +#define arch_mcs_spin_lock_contended(l) > \ > +do { \ > + int locked_val; \ > + for (;;) { \ > + locked_val = READ_ONCE(*l); \ > + if (locked_val) \ > + break; \ > + cmpwait(l, locked_val); \ > + } \ > + smp_rmb(); \ > +} while (0)
If you make the generic version use smp_cond_load_acquire() this isn't needed.
