similar to: [PATCH V4] x86 spinlock: Fix memory corruption on completing completions

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which is

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which is

* Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> [2015-02-15 11:25:44]: Resending the V5 with smp_mb__after_atomic() change without bumping up revision ---8<--- >From 0b9ecde30e3bf5b5b24009fd2ac5fc7ac4b81158 Mon Sep 17 00:00:00 2001 From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> Date: Fri, 6 Feb 2015 16:44:11 +0530 Subject: [PATCH RESEND V5] x86 spinlock:

* Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> [2015-02-15 11:25:44]: Resending the V5 with smp_mb__after_atomic() change without bumping up revision ---8<--- >From 0b9ecde30e3bf5b5b24009fd2ac5fc7ac4b81158 Mon Sep 17 00:00:00 2001 From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> Date: Fri, 6 Feb 2015 16:44:11 +0530 Subject: [PATCH RESEND V5] x86 spinlock:

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which is

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which is

In virtualized environment there are mainly three problems related to spinlocks that affects performance. 1. LHP (lock holder preemption) 2. Lock Waiter Preemption (LWP) 3. Starvation/fairness Though Ticketlocks solve fairness problem it worsens LWP, LHP problems. Though pv-ticketlocks tried to address these problems we can further improve at the cost of relaxed fairness. The following patch

In virtualized environment there are mainly three problems related to spinlocks that affects performance. 1. LHP (lock holder preemption) 2. Lock Waiter Preemption (LWP) 3. Starvation/fairness Though Ticketlocks solve fairness problem it worsens LWP, LHP problems. Though pv-ticketlocks tried to address these problems we can further improve at the cost of relaxed fairness. The following patch

In virtualized environment there are mainly three problems related to spinlocks that affect performance. 1. LHP (lock holder preemption) 2. Lock Waiter Preemption (LWP) 3. Starvation/fairness Though ticketlocks solve the fairness problem, it worsens LWP, LHP problems. pv-ticketlocks tried to address this. But we can further improve at the cost of relaxed fairness. In this patch, we form a batch

In virtualized environment there are mainly three problems related to spinlocks that affect performance. 1. LHP (lock holder preemption) 2. Lock Waiter Preemption (LWP) 3. Starvation/fairness Though ticketlocks solve the fairness problem, it worsens LWP, LHP problems. pv-ticketlocks tried to address this. But we can further improve at the cost of relaxed fairness. In this patch, we form a batch

On 02/13/2015 09:02 PM, Oleg Nesterov wrote: > On 02/13, Raghavendra K T wrote: >> >> @@ -164,7 +161,7 @@ static inline 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); >> } >

On 02/13/2015 09:02 PM, Oleg Nesterov wrote: > On 02/13, Raghavendra K T wrote: >> >> @@ -164,7 +161,7 @@ static inline 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); >> } >

To speed up paravirtualized spinlock handling when running on bare metal introduce a new pvops function "clear_slowpath". This is a nop when the kernel is running on bare metal. As the clear_slowpath function is common for all users add a new initialization function to set the pvops function pointer in order to avoid spreading the knowledge which function to use. Signed-off-by: Juergen

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which

Paravirt spinlock clears slowpath flag after doing unlock. As explained by Linus currently it does: prev = *lock; add_smp(&lock->tickets.head, TICKET_LOCK_INC); /* add_smp() is a full mb() */ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG)) __ticket_unlock_slowpath(lock, prev); which

The decision whether the slowpath flag is to be cleared for paravirtualized spinlocks is located in __ticket_check_and_clear_slowpath() today. Move that decision into arch_spin_lock() and add an unlikely attribute to it to avoid calling a function in case the compiler chooses not to inline __ticket_check_and_clear_slowpath() and the slowpath flag isn't set. Signed-off-by: Juergen Gross

On 02/06/2015 06:49 AM, Raghavendra K T wrote: > Paravirt spinlock clears slowpath flag after doing unlock. > As explained by Linus currently it does: > prev = *lock; > add_smp(&lock->tickets.head, TICKET_LOCK_INC); > > /* add_smp() is a full mb() */ > > if (unlikely(lock->tickets.tail &

On 02/06/2015 06:49 AM, Raghavendra K T wrote: > Paravirt spinlock clears slowpath flag after doing unlock. > As explained by Linus currently it does: > prev = *lock; > add_smp(&lock->tickets.head, TICKET_LOCK_INC); > > /* add_smp() is a full mb() */ > > if (unlikely(lock->tickets.tail &