search for: tickets_equ

...lock() could simply do head = xadd(&lock->tickets.head, TICKET_LOCK_INC); if (head & TICKET_SLOWPATH_FLAG) __ticket_unlock_kick(head); so it can't overflow to .tail? But probably I missed your concern. And we we do this, probably it makes sense to add something like bool tickets_equal(__ticket_t one, __ticket_t two) { return (one ^ two) & ~TICKET_SLOWPATH_FLAG; } and change kvm_lock_spinning() to use tickets_equal(tickets.head, want), plus it can have more users in asm/spinlock.h. Oleg.

...lock() could simply do head = xadd(&lock->tickets.head, TICKET_LOCK_INC); if (head & TICKET_SLOWPATH_FLAG) __ticket_unlock_kick(head); so it can't overflow to .tail? But probably I missed your concern. And we we do this, probably it makes sense to add something like bool tickets_equal(__ticket_t one, __ticket_t two) { return (one ^ two) & ~TICKET_SLOWPATH_FLAG; } and change kvm_lock_spinning() to use tickets_equal(tickets.head, want), plus it can have more users in asm/spinlock.h. Oleg.

On 02/10, Raghavendra K T wrote: > > On 02/10/2015 06:23 AM, Linus Torvalds wrote: > >> add_smp(&lock->tickets.head, TICKET_LOCK_INC); >> if (READ_ONCE(lock->tickets.tail) & TICKET_SLOWPATH_FLAG) .. >> >> into something like >> >> val = xadd((&lock->ticket.head_tail, TICKET_LOCK_INC << TICKET_SHIFT);

On 02/10, Raghavendra K T wrote: > > On 02/10/2015 06:23 AM, Linus Torvalds wrote: > >> add_smp(&lock->tickets.head, TICKET_LOCK_INC); >> if (READ_ONCE(lock->tickets.tail) & TICKET_SLOWPATH_FLAG) .. >> >> into something like >> >> val = xadd((&lock->ticket.head_tail, TICKET_LOCK_INC << TICKET_SHIFT);

...int arch_spin_is_locked(arch_spinlock_t *lock) >> { >> struct __raw_tickets tmp = READ_ONCE(lock->tickets); >> >> - return tmp.tail != tmp.head; >> + return tmp.tail != (tmp.head & ~TICKET_SLOWPATH_FLAG); >> } > > Well, this can probably use __tickets_equal() too. But this is cosmetic. That looks good. Added. > It seems that arch_spin_is_contended() should be fixed with this change, > > (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC > > can be true because of TICKET_SLOWPATH_FLAG in .head, even if it is actually > unlock...

...int arch_spin_is_locked(arch_spinlock_t *lock) >> { >> struct __raw_tickets tmp = READ_ONCE(lock->tickets); >> >> - return tmp.tail != tmp.head; >> + return tmp.tail != (tmp.head & ~TICKET_SLOWPATH_FLAG); >> } > > Well, this can probably use __tickets_equal() too. But this is cosmetic. That looks good. Added. > It seems that arch_spin_is_contended() should be fixed with this change, > > (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC > > can be true because of TICKET_SLOWPATH_FLAG in .head, even if it is actually > unlock...

...rnel/kvm.c | 10 +++-- arch/x86/xen/spinlock.c | 10 +++-- 3 files changed, 59 insertions(+), 56 deletions(-) potential TODO: * The whole patch be splitted into, 1. move slowpath flag 2. fix memory corruption in completion problem ?? Changes since V4: - one more usage of tickets_equal() (Oleg) - head > tail situation can lead to false contended check (Oleg) - smp_mb__after_atomic() added after slowptha_enter (Oleg) Changes since V3: - Detailed changelog (PeterZ) - Replace ACCESS_ONCE with READ_ONCE (oleg) - Add xen changes (Oleg) - Correct break logic in unlock...

...rnel/kvm.c | 10 +++-- arch/x86/xen/spinlock.c | 10 +++-- 3 files changed, 59 insertions(+), 56 deletions(-) potential TODO: * The whole patch be splitted into, 1. move slowpath flag 2. fix memory corruption in completion problem ?? Changes since V4: - one more usage of tickets_equal() (Oleg) - head > tail situation can lead to false contended check (Oleg) - smp_mb__after_atomic() added after slowptha_enter (Oleg) Changes since V3: - Detailed changelog (PeterZ) - Replace ACCESS_ONCE with READ_ONCE (oleg) - Add xen changes (Oleg) - Correct break logic in unlock...

...rnel/kvm.c | 10 +++-- arch/x86/xen/spinlock.c | 10 +++-- 3 files changed, 59 insertions(+), 56 deletions(-) potential TODO: * The whole patch be splitted into, 1. move slowpath flag 2. fix memory corruption in completion problem ?? Changes since V4: - one more usage of tickets_equal() (Oleg) - head > tail situation can lead to false contended check (Oleg) Changes since V3: - Detailed changelog (PeterZ) - Replace ACCESS_ONCE with READ_ONCE (oleg) - Add xen changes (Oleg) - Correct break logic in unlock_wait() (Oleg) Changes since V2: - Move the slowpath flag...

...rnel/kvm.c | 10 +++-- arch/x86/xen/spinlock.c | 10 +++-- 3 files changed, 59 insertions(+), 56 deletions(-) potential TODO: * The whole patch be splitted into, 1. move slowpath flag 2. fix memory corruption in completion problem ?? Changes since V4: - one more usage of tickets_equal() (Oleg) - head > tail situation can lead to false contended check (Oleg) Changes since V3: - Detailed changelog (PeterZ) - Replace ACCESS_ONCE with READ_ONCE (oleg) - Add xen changes (Oleg) - Correct break logic in unlock_wait() (Oleg) Changes since V2: - Move the slowpath flag...

...7 ++- arch/x86/xen/spinlock.c | 7 ++- 3 files changed, 58 insertions(+), 50 deletions(-) Changes for stable: - Don't replace the ACCESS_ONCE to READ_ONCE which would cause horraneous Compiler warnings (Linus, David Vbriel, PeterZ, Ingo) Changes since V4: - one more usage of tickets_equal() (Oleg) - head > tail situation can lead to false contended check (Oleg) - smp_mb__after_atomic() added after slowptha_enter (Oleg) Changes since V3: - Detailed changelog (PeterZ) - Replace ACCESS_ONCE with READ_ONCE (oleg) - Add xen changes (Oleg) - Correct break logic in unlock...

...7 ++- arch/x86/xen/spinlock.c | 7 ++- 3 files changed, 58 insertions(+), 50 deletions(-) Changes for stable: - Don't replace the ACCESS_ONCE to READ_ONCE which would cause horraneous Compiler warnings (Linus, David Vbriel, PeterZ, Ingo) Changes since V4: - one more usage of tickets_equal() (Oleg) - head > tail situation can lead to false contended check (Oleg) - smp_mb__after_atomic() added after slowptha_enter (Oleg) Changes since V3: - Detailed changelog (PeterZ) - Replace ACCESS_ONCE with READ_ONCE (oleg) - Add xen changes (Oleg) - Correct break logic in unlock...