For qspinlocks on ARM64, we would like to use WFE instead of purely spinning. Qspinlocks internally have lock contenders spin on an MCS lock.
Update arch_mcs_spin_lock_contended() such that it uses the new smp_cond_load_acquire() so that ARM64 can also override this spin loop with its own implementation using WFE. On x86, it can also cheaper to use this than spinning on smp_load_acquire(). Signed-off-by: Jason Low <[email protected]> --- Changes from v1: - Pass l instead of &l to smp_cond_load_acquire() since l is already a pointer to the lock variable. kernel/locking/mcs_spinlock.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index c835270..1c55987 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -22,13 +22,13 @@ struct mcs_spinlock { #ifndef arch_mcs_spin_lock_contended /* - * Using smp_load_acquire() provides a memory barrier that ensures - * subsequent operations happen after the lock is acquired. + * Using smp_cond_load_acquire() provides the acquire semantics + * required so that subsequent operations happen after the + * lock is acquired. */ #define arch_mcs_spin_lock_contended(l) \ do { \ - while (!(smp_load_acquire(l))) \ - cpu_relax_lowlatency(); \ + smp_cond_load_acquire(l, VAL); \ } while (0) #endif -- 2.1.4
