Commit 964705c4 authored by Sebastian Sanchez's avatar Sebastian Sanchez Committed by Greg Kroah-Hartman

IB/hfi1: Optimize kthread pointer locking when queuing CQ entries

commit af8aab71370a692eaf7e7969ba5b1a455ac20113 upstream.

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: 's avatarMike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: 's avatarSebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: 's avatarDennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: 's avatarDoug Ledford <dledford@redhat.com>
Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2bd28cba
......@@ -121,17 +121,20 @@ 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);
......@@ -513,7 +516,7 @@ 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);
......@@ -525,7 +528,7 @@ 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;
}
......@@ -537,15 +540,19 @@ 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);
}
......@@ -409,7 +409,7 @@ 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 */
......
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