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Commit af8aab71 authored by Sebastian Sanchez's avatar Sebastian Sanchez Committed by Doug Ledford
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IB/hfi1: Optimize kthread pointer locking when queuing CQ entries 



All threads queuing CQ entries on different CQs are unnecessarily
synchronized by a spin lock to check if the CQ kthread worker hasn't
been destroyed before queuing an CQ entry.

The lock used in 6efaf10f ("IB/rdmavt: Avoid queuing work into a
destroyed cq kthread worker") is a device global lock and will have
poor performance at scale as completions are entered from a large
number of CPUs.

Convert to use RCU where the read side of RCU is rvt_cq_enter() to
determine that the worker is alive prior to triggering the
completion event.
Apply write side RCU semantics in rvt_driver_cq_init() and
rvt_cq_exit().

Fixes: 6efaf10f ("IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker")
Cc: <stable@vger.kernel.org> # 4.14.x
Reviewed-by: default avatarMike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: default avatarSebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: default avatarDennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
parent c872a1f9

drivers/infiniband/sw/rdmavt/cq.c

+19 −12
Original line number Diff line number Diff line
@@ -120,17 +120,20 @@ void rvt_cq_enter(struct rvt_cq *cq, struct ib_wc *entry, bool solicited) 
	if (cq->notify == IB_CQ_NEXT_COMP ||

	    (cq->notify == IB_CQ_SOLICITED &&

	     (solicited || entry->status != IB_WC_SUCCESS))) {

		struct kthread_worker *worker;



		/*

		 * This will cause send_complete() to be called in

		 * another thread.

		 */

		spin_lock(&cq->rdi->n_cqs_lock);

		if (likely(cq->rdi->worker)) {

		rcu_read_lock();

		worker = rcu_dereference(cq->rdi->worker);

		if (likely(worker)) {

			cq->notify = RVT_CQ_NONE;

			cq->triggered++;

			kthread_queue_work(cq->rdi->worker, &cq->comptask);

			kthread_queue_work(worker, &cq->comptask);

		}

		spin_unlock(&cq->rdi->n_cqs_lock);

		rcu_read_unlock();

	}



	spin_unlock_irqrestore(&cq->lock, flags);
@@ -512,7 +515,7 @@ int rvt_driver_cq_init(struct rvt_dev_info *rdi) 
	int cpu;

	struct kthread_worker *worker;



	if (rdi->worker)

	if (rcu_access_pointer(rdi->worker))

		return 0;



	spin_lock_init(&rdi->n_cqs_lock);
@@ -524,7 +527,7 @@ int rvt_driver_cq_init(struct rvt_dev_info *rdi) 
		return PTR_ERR(worker);



	set_user_nice(worker->task, MIN_NICE);

	rdi->worker = worker;

	RCU_INIT_POINTER(rdi->worker, worker);

	return 0;

}
@@ -536,15 +539,19 @@ void rvt_cq_exit(struct rvt_dev_info *rdi) 
{

	struct kthread_worker *worker;



	/* block future queuing from send_complete() */

	spin_lock_irq(&rdi->n_cqs_lock);

	worker = rdi->worker;

	if (!rcu_access_pointer(rdi->worker))

		return;



	spin_lock(&rdi->n_cqs_lock);

	worker = rcu_dereference_protected(rdi->worker,

					   lockdep_is_held(&rdi->n_cqs_lock));

	if (!worker) {

		spin_unlock_irq(&rdi->n_cqs_lock);

		spin_unlock(&rdi->n_cqs_lock);

		return;

	}

	rdi->worker = NULL;

	spin_unlock_irq(&rdi->n_cqs_lock);

	RCU_INIT_POINTER(rdi->worker, NULL);

	spin_unlock(&rdi->n_cqs_lock);

	synchronize_rcu();



	kthread_destroy_worker(worker);

}

include/rdma/rdma_vt.h

+1 −1
Original line number Diff line number Diff line
@@ -402,7 +402,7 @@ struct rvt_dev_info { 
	spinlock_t pending_lock; /* protect pending mmap list */



	/* CQ */

	struct kthread_worker *worker; /* per device cq worker */

	struct kthread_worker __rcu *worker; /* per device cq worker */

	u32 n_cqs_allocated;    /* number of CQs allocated for device */

	spinlock_t n_cqs_lock; /* protect count of in use cqs */