io_uring: mutex locked poll hashing
Currently we do two extra spin lock/unlock pairs to add a poll/apoll
request to the cancellation hash table and remove it from there.
On the submission side we often already hold ->uring_lock and tw
completion is likely to hold it as well. Add a second cancellation hash
table protected by ->uring_lock. In concerns for latency because of a
need to have the mutex locked on the completion side, use the new table
only in following cases:
1) IORING_SETUP_SINGLE_ISSUER: only one task grabs uring_lock, so there
is little to no contention and so the main tw hander will almost
always end up grabbing it before calling callbacks.
2) IORING_SETUP_SQPOLL: same as with single issuer, only one task is
a major user of ->uring_lock.
3) apoll: we normally grab the lock on the completion side anyway to
execute the request, so it's free.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1bbad9c78c454b7b92f100bbf46730a37df7194f.1655371007.git.asml.silence@gmail.com
Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 0b3851a..eeda167 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -275,6 +275,8 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
hash_bits = clamp(hash_bits, 1, 8);
if (io_alloc_hash_table(&ctx->cancel_table, hash_bits))
goto err;
+ if (io_alloc_hash_table(&ctx->cancel_table_locked, hash_bits))
+ goto err;
ctx->dummy_ubuf = kzalloc(sizeof(*ctx->dummy_ubuf), GFP_KERNEL);
if (!ctx->dummy_ubuf)
@@ -317,6 +319,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
err:
kfree(ctx->dummy_ubuf);
kfree(ctx->cancel_table.hbs);
+ kfree(ctx->cancel_table_locked.hbs);
kfree(ctx->io_bl);
xa_destroy(&ctx->io_bl_xa);
kfree(ctx);
@@ -2493,6 +2496,7 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
if (ctx->hash_map)
io_wq_put_hash(ctx->hash_map);
kfree(ctx->cancel_table.hbs);
+ kfree(ctx->cancel_table_locked.hbs);
kfree(ctx->dummy_ubuf);
kfree(ctx->io_bl);
xa_destroy(&ctx->io_bl_xa);
@@ -2654,12 +2658,13 @@ static __cold void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
__io_cqring_overflow_flush(ctx, true);
xa_for_each(&ctx->personalities, index, creds)
io_unregister_personality(ctx, index);
+ if (ctx->rings)
+ io_poll_remove_all(ctx, NULL, true);
mutex_unlock(&ctx->uring_lock);
/* failed during ring init, it couldn't have issued any requests */
if (ctx->rings) {
io_kill_timeouts(ctx, NULL, true);
- io_poll_remove_all(ctx, NULL, true);
/* if we failed setting up the ctx, we might not have any rings */
io_iopoll_try_reap_events(ctx);
}
@@ -2784,7 +2789,9 @@ static __cold void io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
}
ret |= io_cancel_defer_files(ctx, task, cancel_all);
+ mutex_lock(&ctx->uring_lock);
ret |= io_poll_remove_all(ctx, task, cancel_all);
+ mutex_unlock(&ctx->uring_lock);
ret |= io_kill_timeouts(ctx, task, cancel_all);
if (task)
ret |= io_run_task_work();
diff --git a/io_uring/io_uring_types.h b/io_uring/io_uring_types.h
index d3b9bde..65ac7cd 100644
--- a/io_uring/io_uring_types.h
+++ b/io_uring/io_uring_types.h
@@ -191,6 +191,7 @@ struct io_ring_ctx {
struct xarray io_bl_xa;
struct list_head io_buffers_cache;
+ struct io_hash_table cancel_table_locked;
struct list_head cq_overflow_list;
struct list_head apoll_cache;
struct xarray personalities;
@@ -323,6 +324,7 @@ enum {
REQ_F_CQE32_INIT_BIT,
REQ_F_APOLL_MULTISHOT_BIT,
REQ_F_CLEAR_POLLIN_BIT,
+ REQ_F_HASH_LOCKED_BIT,
/* keep async read/write and isreg together and in order */
REQ_F_SUPPORT_NOWAIT_BIT,
REQ_F_ISREG_BIT,
@@ -393,6 +395,8 @@ enum {
REQ_F_CQE32_INIT = BIT(REQ_F_CQE32_INIT_BIT),
/* recvmsg special flag, clear EPOLLIN */
REQ_F_CLEAR_POLLIN = BIT(REQ_F_CLEAR_POLLIN_BIT),
+ /* hashed into ->cancel_hash_locked, protected by ->uring_lock */
+ REQ_F_HASH_LOCKED = BIT(REQ_F_HASH_LOCKED_BIT),
};
typedef void (*io_req_tw_func_t)(struct io_kiocb *req, bool *locked);
diff --git a/io_uring/poll.c b/io_uring/poll.c
index c4edf87..9ae2982 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -93,6 +93,32 @@ static void io_poll_req_delete(struct io_kiocb *req, struct io_ring_ctx *ctx)
spin_unlock(lock);
}
+static void io_poll_req_insert_locked(struct io_kiocb *req)
+{
+ struct io_hash_table *table = &req->ctx->cancel_table_locked;
+ u32 index = hash_long(req->cqe.user_data, table->hash_bits);
+
+ hlist_add_head(&req->hash_node, &table->hbs[index].list);
+}
+
+static void io_poll_tw_hash_eject(struct io_kiocb *req, bool *locked)
+{
+ struct io_ring_ctx *ctx = req->ctx;
+
+ if (req->flags & REQ_F_HASH_LOCKED) {
+ /*
+ * ->cancel_table_locked is protected by ->uring_lock in
+ * contrast to per bucket spinlocks. Likely, tctx_task_work()
+ * already grabbed the mutex for us, but there is a chance it
+ * failed.
+ */
+ io_tw_lock(ctx, locked);
+ hash_del(&req->hash_node);
+ } else {
+ io_poll_req_delete(req, ctx);
+ }
+}
+
static void io_init_poll_iocb(struct io_poll *poll, __poll_t events,
wait_queue_func_t wake_func)
{
@@ -217,7 +243,6 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked)
static void io_poll_task_func(struct io_kiocb *req, bool *locked)
{
- struct io_ring_ctx *ctx = req->ctx;
int ret;
ret = io_poll_check_events(req, locked);
@@ -234,7 +259,8 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
}
io_poll_remove_entries(req);
- io_poll_req_delete(req, ctx);
+ io_poll_tw_hash_eject(req, locked);
+
io_req_set_res(req, req->cqe.res, 0);
io_req_task_complete(req, locked);
}
@@ -248,7 +274,7 @@ static void io_apoll_task_func(struct io_kiocb *req, bool *locked)
return;
io_poll_remove_entries(req);
- io_poll_req_delete(req, req->ctx);
+ io_poll_tw_hash_eject(req, locked);
if (!ret)
io_req_task_submit(req, locked);
@@ -444,7 +470,10 @@ static int __io_arm_poll_handler(struct io_kiocb *req,
return 0;
}
- io_poll_req_insert(req);
+ if (req->flags & REQ_F_HASH_LOCKED)
+ io_poll_req_insert_locked(req);
+ else
+ io_poll_req_insert(req);
if (mask && (poll->events & EPOLLET)) {
/* can't multishot if failed, just queue the event we've got */
@@ -485,6 +514,15 @@ int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
__poll_t mask = POLLPRI | POLLERR | EPOLLET;
int ret;
+ /*
+ * apoll requests already grab the mutex to complete in the tw handler,
+ * so removal from the mutex-backed hash is free, use it by default.
+ */
+ if (issue_flags & IO_URING_F_UNLOCKED)
+ req->flags &= ~REQ_F_HASH_LOCKED;
+ else
+ req->flags |= REQ_F_HASH_LOCKED;
+
if (!def->pollin && !def->pollout)
return IO_APOLL_ABORTED;
if (!file_can_poll(req->file))
@@ -534,13 +572,10 @@ int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
return IO_APOLL_OK;
}
-/*
- * Returns true if we found and killed one or more poll requests
- */
-__cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk,
- bool cancel_all)
+static __cold bool io_poll_remove_all_table(struct task_struct *tsk,
+ struct io_hash_table *table,
+ bool cancel_all)
{
- struct io_hash_table *table = &ctx->cancel_table;
unsigned nr_buckets = 1U << table->hash_bits;
struct hlist_node *tmp;
struct io_kiocb *req;
@@ -563,6 +598,17 @@ __cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk,
return found;
}
+/*
+ * Returns true if we found and killed one or more poll requests
+ */
+__cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk,
+ bool cancel_all)
+ __must_hold(&ctx->uring_lock)
+{
+ return io_poll_remove_all_table(tsk, &ctx->cancel_table, cancel_all) |
+ io_poll_remove_all_table(tsk, &ctx->cancel_table_locked, cancel_all);
+}
+
static struct io_kiocb *io_poll_find(struct io_ring_ctx *ctx, bool poll_only,
struct io_cancel_data *cd,
struct io_hash_table *table,
@@ -622,13 +668,15 @@ static struct io_kiocb *io_poll_file_find(struct io_ring_ctx *ctx,
return NULL;
}
-static bool io_poll_disarm(struct io_kiocb *req)
+static int io_poll_disarm(struct io_kiocb *req)
{
+ if (!req)
+ return -ENOENT;
if (!io_poll_get_ownership(req))
- return false;
+ return -EALREADY;
io_poll_remove_entries(req);
hash_del(&req->hash_node);
- return true;
+ return 0;
}
static int __io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
@@ -652,7 +700,16 @@ static int __io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
int io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
unsigned issue_flags)
{
- return __io_poll_cancel(ctx, cd, &ctx->cancel_table);
+ int ret;
+
+ ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table);
+ if (ret != -ENOENT)
+ return ret;
+
+ io_ring_submit_lock(ctx, issue_flags);
+ ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table_locked);
+ io_ring_submit_unlock(ctx, issue_flags);
+ return ret;
}
static __poll_t io_poll_parse_events(const struct io_uring_sqe *sqe,
@@ -727,6 +784,16 @@ int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
ipt.pt._qproc = io_poll_queue_proc;
+ /*
+ * If sqpoll or single issuer, there is no contention for ->uring_lock
+ * and we'll end up holding it in tw handlers anyway.
+ */
+ if (!(issue_flags & IO_URING_F_UNLOCKED) &&
+ (req->ctx->flags & (IORING_SETUP_SQPOLL | IORING_SETUP_SINGLE_ISSUER)))
+ req->flags |= REQ_F_HASH_LOCKED;
+ else
+ req->flags &= ~REQ_F_HASH_LOCKED;
+
ret = __io_arm_poll_handler(req, poll, &ipt, poll->events);
if (ret) {
io_req_set_res(req, ret, 0);
@@ -751,20 +818,28 @@ int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags)
bool locked;
preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table, &bucket);
- if (preq)
- ret2 = io_poll_disarm(preq);
+ ret2 = io_poll_disarm(preq);
if (bucket)
spin_unlock(&bucket->lock);
-
- if (!preq) {
- ret = -ENOENT;
- goto out;
- }
- if (!ret2) {
- ret = -EALREADY;
+ if (!ret2)
+ goto found;
+ if (ret2 != -ENOENT) {
+ ret = ret2;
goto out;
}
+ io_ring_submit_lock(ctx, issue_flags);
+ preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table_locked, &bucket);
+ ret2 = io_poll_disarm(preq);
+ if (bucket)
+ spin_unlock(&bucket->lock);
+ io_ring_submit_unlock(ctx, issue_flags);
+ if (ret2) {
+ ret = ret2;
+ goto out;
+ }
+
+found:
if (poll_update->update_events || poll_update->update_user_data) {
/* only mask one event flags, keep behavior flags */
if (poll_update->update_events) {
