[PATCH 07/15] IB/hfi1: Improve performance of interval RB trees

Dennis Dalessandro
2016-05-12T17:23:09Z

From: Mitko Haralanov <mitko.haralanov-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

The interval RB tree management functions use handlers to
store user-specific callback for the various tree operations.
These handlers are put on a doubly-linked list. When a RB
tree function is called, the list is searched for the handler
of the particular tree.

The list which holds the handlers is modified very rarely - when
a handler is created and when a handler is removed. On the other
hand, it is searched very often. This a perfect usage scenario
for RCU.

The result is a much lower overhead of traversing the list as most
of the time no locking will be required.

Reviewed-by: Dean Luick <dean.luick-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Signed-off-by: Mitko Haralanov <mitko.haralanov-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
drivers/staging/rdma/hfi1/mmu_rb.c | 22 +++++++++++-----------
1 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/staging/rdma/hfi1/mmu_rb.c b/drivers/staging/rdma/hfi1/mmu_rb.c
index 2b0e91d..b7a80aa 100644
--- a/drivers/staging/rdma/hfi1/mmu_rb.c
+++ b/drivers/staging/rdma/hfi1/mmu_rb.c
@@ -45,6 +45,7 @@
*
*/
#include <linux/list.h>
+#include <linux/rculist.h>
#include <linux/mmu_notifier.h>
#include <linux/interval_tree_generic.h>

@@ -97,7 +98,6 @@ static unsigned long mmu_node_last(struct mmu_rb_node *node)
int hfi1_mmu_rb_register(struct rb_root *root, struct mmu_rb_ops *ops)
{
struct mmu_rb_handler *handlr;
- unsigned long flags;

if (!ops->invalidate)
return -EINVAL;
@@ -111,9 +111,9 @@ int hfi1_mmu_rb_register(struct rb_root *root, struct mmu_rb_ops *ops)
INIT_HLIST_NODE(&handlr->mn.hlist);
spin_lock_init(&handlr->lock);
handlr->mn.ops = &mn_opts;
- spin_lock_irqsave(&mmu_rb_lock, flags);
- list_add_tail(&handlr->list, &mmu_rb_handlers);
- spin_unlock_irqrestore(&mmu_rb_lock, flags);
+ spin_lock(&mmu_rb_lock);
+ list_add_tail_rcu(&handlr->list, &mmu_rb_handlers);
+ spin_unlock(&mmu_rb_lock);

return mmu_notifier_register(&handlr->mn, current->mm);
}
@@ -130,9 +130,10 @@ void hfi1_mmu_rb_unregister(struct rb_root *root)
if (current->mm)
mmu_notifier_unregister(&handler->mn, current->mm);

- spin_lock_irqsave(&mmu_rb_lock, flags);
- list_del(&handler->list);
- spin_unlock_irqrestore(&mmu_rb_lock, flags);
+ spin_lock(&mmu_rb_lock);
+ list_del_rcu(&handler->list);
+ spin_unlock(&mmu_rb_lock);
+ synchronize_rcu();

spin_lock_irqsave(&handler->lock, flags);
if (!RB_EMPTY_ROOT(root)) {
@@ -271,16 +272,15 @@ void hfi1_mmu_rb_remove(struct rb_root *root, struct mmu_rb_node *node)
static struct mmu_rb_handler *find_mmu_handler(struct rb_root *root)
{
struct mmu_rb_handler *handler;
- unsigned long flags;

- spin_lock_irqsave(&mmu_rb_lock, flags);
- list_for_each_entry(handler, &mmu_rb_handlers, list) {
+ rcu_read_lock();
+ list_for_each_entry_rcu(handler, &mmu_rb_handlers, list) {
if (handler->root == root)
goto unlock;
}
handler = NULL;
unlock:
- spin_unlock_irqrestore(&mmu_rb_lock, flags);
+ rcu_read_unlock();
return handler;
}