io_uring: use hash table for poll command lookups
We recently changed this from a single list to an rbtree, but for some
real life workloads, the rbtree slows down the submission/insertion
case enough so that it's the top cycle consumer on the io_uring side.
In testing, using a hash table is a more well rounded compromise. It
is fast for insertion, and as long as it's sized appropriately, it
works well for the cancellation case as well. Running TAO with a lot
of network sockets, this removes io_poll_req_insert() from spending
2% of the CPU cycles.
Reported-by: Dan Melnic <dmm@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2efe1ac..8fa6b19 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -275,7 +275,8 @@ struct io_ring_ctx {
* manipulate the list, hence no extra locking is needed there.
*/
struct list_head poll_list;
- struct rb_root cancel_tree;
+ struct hlist_head *cancel_hash;
+ unsigned cancel_hash_bits;
spinlock_t inflight_lock;
struct list_head inflight_list;
@@ -355,7 +356,7 @@ struct io_kiocb {
struct io_ring_ctx *ctx;
union {
struct list_head list;
- struct rb_node rb_node;
+ struct hlist_node hash_node;
};
struct list_head link_list;
unsigned int flags;
@@ -444,6 +445,7 @@ static void io_ring_ctx_ref_free(struct percpu_ref *ref)
static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
{
struct io_ring_ctx *ctx;
+ int hash_bits;
ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
@@ -457,6 +459,21 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
if (!ctx->completions)
goto err;
+ /*
+ * Use 5 bits less than the max cq entries, that should give us around
+ * 32 entries per hash list if totally full and uniformly spread.
+ */
+ hash_bits = ilog2(p->cq_entries);
+ hash_bits -= 5;
+ if (hash_bits <= 0)
+ hash_bits = 1;
+ ctx->cancel_hash_bits = hash_bits;
+ ctx->cancel_hash = kmalloc((1U << hash_bits) * sizeof(struct hlist_head),
+ GFP_KERNEL);
+ if (!ctx->cancel_hash)
+ goto err;
+ __hash_init(ctx->cancel_hash, 1U << hash_bits);
+
if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
PERCPU_REF_ALLOW_REINIT, GFP_KERNEL))
goto err;
@@ -470,7 +487,6 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
init_waitqueue_head(&ctx->wait);
spin_lock_init(&ctx->completion_lock);
INIT_LIST_HEAD(&ctx->poll_list);
- ctx->cancel_tree = RB_ROOT;
INIT_LIST_HEAD(&ctx->defer_list);
INIT_LIST_HEAD(&ctx->timeout_list);
init_waitqueue_head(&ctx->inflight_wait);
@@ -481,6 +497,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
if (ctx->fallback_req)
kmem_cache_free(req_cachep, ctx->fallback_req);
kfree(ctx->completions);
+ kfree(ctx->cancel_hash);
kfree(ctx);
return NULL;
}
@@ -2260,14 +2277,6 @@ static int io_connect(struct io_kiocb *req, const struct io_uring_sqe *sqe,
#endif
}
-static inline void io_poll_remove_req(struct io_kiocb *req)
-{
- if (!RB_EMPTY_NODE(&req->rb_node)) {
- rb_erase(&req->rb_node, &req->ctx->cancel_tree);
- RB_CLEAR_NODE(&req->rb_node);
- }
-}
-
static void io_poll_remove_one(struct io_kiocb *req)
{
struct io_poll_iocb *poll = &req->poll;
@@ -2279,36 +2288,34 @@ static void io_poll_remove_one(struct io_kiocb *req)
io_queue_async_work(req);
}
spin_unlock(&poll->head->lock);
- io_poll_remove_req(req);
+ hash_del(&req->hash_node);
}
static void io_poll_remove_all(struct io_ring_ctx *ctx)
{
- struct rb_node *node;
+ struct hlist_node *tmp;
struct io_kiocb *req;
+ int i;
spin_lock_irq(&ctx->completion_lock);
- while ((node = rb_first(&ctx->cancel_tree)) != NULL) {
- req = rb_entry(node, struct io_kiocb, rb_node);
- io_poll_remove_one(req);
+ for (i = 0; i < (1U << ctx->cancel_hash_bits); i++) {
+ struct hlist_head *list;
+
+ list = &ctx->cancel_hash[i];
+ hlist_for_each_entry_safe(req, tmp, list, hash_node)
+ io_poll_remove_one(req);
}
spin_unlock_irq(&ctx->completion_lock);
}
static int io_poll_cancel(struct io_ring_ctx *ctx, __u64 sqe_addr)
{
- struct rb_node *p, *parent = NULL;
+ struct hlist_head *list;
struct io_kiocb *req;
- p = ctx->cancel_tree.rb_node;
- while (p) {
- parent = p;
- req = rb_entry(parent, struct io_kiocb, rb_node);
- if (sqe_addr < req->user_data) {
- p = p->rb_left;
- } else if (sqe_addr > req->user_data) {
- p = p->rb_right;
- } else {
+ list = &ctx->cancel_hash[hash_long(sqe_addr, ctx->cancel_hash_bits)];
+ hlist_for_each_entry(req, list, hash_node) {
+ if (sqe_addr == req->user_data) {
io_poll_remove_one(req);
return 0;
}
@@ -2390,7 +2397,7 @@ static void io_poll_complete_work(struct io_wq_work **workptr)
spin_unlock_irq(&ctx->completion_lock);
return;
}
- io_poll_remove_req(req);
+ hash_del(&req->hash_node);
io_poll_complete(req, mask, ret);
spin_unlock_irq(&ctx->completion_lock);
@@ -2425,7 +2432,7 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
* for finalizing the request, mark us as having grabbed that already.
*/
if (mask && spin_trylock_irqsave(&ctx->completion_lock, flags)) {
- io_poll_remove_req(req);
+ hash_del(&req->hash_node);
io_poll_complete(req, mask, 0);
req->flags |= REQ_F_COMP_LOCKED;
io_put_req(req);
@@ -2463,20 +2470,10 @@ static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
static void io_poll_req_insert(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
- struct rb_node **p = &ctx->cancel_tree.rb_node;
- struct rb_node *parent = NULL;
- struct io_kiocb *tmp;
+ struct hlist_head *list;
- while (*p) {
- parent = *p;
- tmp = rb_entry(parent, struct io_kiocb, rb_node);
- if (req->user_data < tmp->user_data)
- p = &(*p)->rb_left;
- else
- p = &(*p)->rb_right;
- }
- rb_link_node(&req->rb_node, parent, p);
- rb_insert_color(&req->rb_node, &ctx->cancel_tree);
+ list = &ctx->cancel_hash[hash_long(req->user_data, ctx->cancel_hash_bits)];
+ hlist_add_head(&req->hash_node, list);
}
static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe,
@@ -2504,7 +2501,7 @@ static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe,
INIT_IO_WORK(&req->work, io_poll_complete_work);
events = READ_ONCE(sqe->poll_events);
poll->events = demangle_poll(events) | EPOLLERR | EPOLLHUP;
- RB_CLEAR_NODE(&req->rb_node);
+ INIT_HLIST_NODE(&req->hash_node);
poll->head = NULL;
poll->done = false;
@@ -4644,6 +4641,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
free_uid(ctx->user);
put_cred(ctx->creds);
kfree(ctx->completions);
+ kfree(ctx->cancel_hash);
kmem_cache_free(req_cachep, ctx->fallback_req);
kfree(ctx);
}
