Messages in this thread Patch in this message | | | Date | Wed, 20 Jan 2021 13:42:53 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 3/3] kvfree_rcu: use migrate_disable/enable() |
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On Wed, Jan 20, 2021 at 08:45:54PM +0100, Sebastian Andrzej Siewior wrote: > On 2021-01-20 17:21:48 [+0100], Uladzislau Rezki (Sony) wrote: > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -3489,10 +3489,12 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp, > > (*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) { > > bnode = get_cached_bnode(*krcp); > > if (!bnode && can_alloc) { > > + migrate_disable(); > > krc_this_cpu_unlock(*krcp, *flags); > > Why is krc_this_cpu_unlock() defined as > | static inline void > | krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags) > | { > | raw_spin_unlock(&krcp->lock); > | local_irq_restore(flags); > | } > > instead of raw_spin_unlock_irqrestore()? > Should something with the locked section trigger a scheduling event by > setting TIF_NEED_RESCHED then there will be no scheduling event on > unlock. It will be delayed until a later "random" preempt_enable(). > > raw_spin_unlock_irqrestore() will reschedule if the flag is set, > local_irq_restore() will not.
Good catch, thank you! This one is already in mainline, so I queued the following patch.
Thanx, Paul
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commit 6c1d51e012c5b474cda77d4fa644d76e041c1e05 Author: Paul E. McKenney <paulmck@kernel.org> Date: Wed Jan 20 13:38:08 2021 -0800
kvfree_rcu: Make krc_this_cpu_unlock() use raw_spin_unlock_irqrestore() The krc_this_cpu_unlock() function does a raw_spin_unlock() immediately followed by a local_irq_restore(). This commit saves a line of code by merging them into a raw_spin_unlock_irqrestore(). This transformation also reduces scheduling latency because raw_spin_unlock_irqrestore() responds immediately to a reschedule request. In contrast, local_irq_restore() does a scheduling-oblivious enabling of interrupts. Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cad3607..e7a226a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3201,8 +3201,7 @@ krc_this_cpu_lock(unsigned long *flags) static inline void krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags) { - raw_spin_unlock(&krcp->lock); - local_irq_restore(flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); } static inline struct kvfree_rcu_bulk_data *
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