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

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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 6efaf10f16 ("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: 6efaf10f16 ("IB/rdmavt: Avoid queuing work into a destroyed cq kthread worker")
Cc: <[email protected]> # 4.14.x
Reviewed-by: Mike Marciniszyn <[email protected]>
Signed-off-by: Sebastian Sanchez <[email protected]>
Signed-off-by: Dennis Dalessandro <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>
This commit is contained in:
Sebastian Sanchez 2018-05-02 06:43:39 -07:00 • committed by Doug Ledford
commit af8aab7137
2 changed files with 20 additions and 13 deletions
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2
include/rdma/rdma_vt.h
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@ -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 */