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IB/core: use RCU for uverbs id lookup

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The current implementation gets a spin_lock, and at any scale with
qib and hfi1 post send, the lock contention grows exponentially
with the number of QPs.

idr_find() is RCU compatibile, so read doesn't need the lock.

Change to use rcu_read_lock() and rcu_read_unlock() in
__idr_get_uobj().

kfree_rcu() is used to insure a grace period between the
idr removal and actual free.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-By: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
This commit is contained in:
Mike Marciniszyn 2015-11-02 12:13:25 -05:00 committed by Doug Ledford
parent 57ab251213
commit d144da8c6f
2 changed files with 8 additions and 5 deletions
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12
drivers/infiniband/core/uverbs_cmd.c
View file

@ -62,9 +62,11 @@ static struct uverbs_lock_class rule_lock_class = { .name = "RULE-uobj" };
* The ib_uobject locking scheme is as follows:
*
* - ib_uverbs_idr_lock protects the uverbs idrs themselves, so it
* needs to be held during all idr operations. When an object is
* needs to be held during all idr write operations. When an object is
* looked up, a reference must be taken on the object's kref before
* dropping this lock.
* dropping this lock. For read operations, the rcu_read_lock()
* and rcu_write_lock() but similarly the kref reference is grabbed
* before the rcu_read_unlock().
*
* - Each object also has an rwsem. This rwsem must be held for
* reading while an operation that uses the object is performed.
@ -96,7 +98,7 @@ static void init_uobj(struct ib_uobject *uobj, u64 user_handle,
static void release_uobj(struct kref *kref)
{
kfree(container_of(kref, struct ib_uobject, ref));
kfree_rcu(container_of(kref, struct ib_uobject, ref), rcu);
}
static void put_uobj(struct ib_uobject *uobj)
@ -145,7 +147,7 @@ static struct ib_uobject *__idr_get_uobj(struct idr *idr, int id,
{
struct ib_uobject *uobj;
spin_lock(&ib_uverbs_idr_lock);
rcu_read_lock();
uobj = idr_find(idr, id);
if (uobj) {
if (uobj->context == context)
@ -153,7 +155,7 @@ static struct ib_uobject *__idr_get_uobj(struct idr *idr, int id,
else
uobj = NULL;
}
spin_unlock(&ib_uverbs_idr_lock);
rcu_read_unlock();
return uobj;
}

1
include/rdma/ib_verbs.h
View file

@ -1271,6 +1271,7 @@ struct ib_uobject {
int id; /* index into kernel idr */
struct kref ref;
struct rw_semaphore mutex; /* protects .live */
struct rcu_head rcu; /* kfree_rcu() overhead */
int live;
};