[PATCH v3 2/2] io_uring: Add support for napi_busy_poll

[Olivier Langlois]

The sqpoll thread can be used for performing the napi busy poll in a
similar way that it does io polling for file systems supporting direct
access bypassing the page cache.

The other way that io_uring can be used for napi busy poll is by
calling io_uring_enter() to get events.

If the user specify a timeout value, it is distributed between polling
and sleeping by using the systemwide setting
/proc/sys/net/core/busy_poll.

v2:
 * Evaluate list_empty(&ctx->napi_list) outside io_napi_busy_loop() to keep
   __io_sq_thread() execution as fast as possible
 * In io_cqring_wait(), move up the sig block to avoid needless computation
   if the block exits the function
 * In io_cqring_wait(), protect ctx->napi_list from race condition by
   splicing it into a local list
 * In io_cqring_wait(), allow busy polling when uts is missing
 * Fix kernel test robot issues
v3:
 * Fix do_div() type mismatch warning
 * Reduce uring_lock contention by creating a spinlock for protecting
   napi_list
 * Support correctly MULTISHOT poll requests

Co-developed-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
Signed-off-by: Olivier Langlois <olivier@xxxxxxxxxxxxxx>
---
 fs/io_uring.c | 230 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 229 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f7b8df79a02b..37c065786e4b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -63,6 +63,7 @@
 #include <net/sock.h>
 #include <net/af_unix.h>
 #include <net/scm.h>
+#include <net/busy_poll.h>
 #include <linux/anon_inodes.h>
 #include <linux/sched/mm.h>
 #include <linux/uaccess.h>
@@ -395,6 +396,11 @@ struct io_ring_ctx {
 	struct list_head	sqd_list;
 
 	unsigned long		check_cq_overflow;
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	/* used to track busy poll napi_id */
+	struct list_head	napi_list;
+	spinlock_t		napi_lock;	/* napi_list lock */
+#endif
 
 	struct {
 		unsigned		cached_cq_tail;
@@ -1464,6 +1470,10 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	INIT_WQ_LIST(&ctx->locked_free_list);
 	INIT_DELAYED_WORK(&ctx->fallback_work, io_fallback_req_func);
 	INIT_WQ_LIST(&ctx->submit_state.compl_reqs);
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	INIT_LIST_HEAD(&ctx->napi_list);
+	spin_lock_init(&ctx->napi_lock);
+#endif
 	return ctx;
 err:
 	kfree(ctx->dummy_ubuf);
@@ -5399,6 +5409,108 @@ IO_NETOP_FN(send);
 IO_NETOP_FN(recv);
 #endif /* CONFIG_NET */
 
+#ifdef CONFIG_NET_RX_BUSY_POLL
+
+#define NAPI_TIMEOUT			(60 * SEC_CONVERSION)
+
+struct napi_entry {
+	struct list_head	list;
+	unsigned int		napi_id;
+	unsigned long		timeout;
+};
+
+/*
+ * Add busy poll NAPI ID from sk.
+ */
+static void io_add_napi(struct file *file, struct io_ring_ctx *ctx)
+{
+	unsigned int napi_id;
+	struct socket *sock;
+	struct sock *sk;
+	struct napi_entry *ne;
+
+	if (!net_busy_loop_on())
+		return;
+
+	sock = sock_from_file(file);
+	if (!sock)
+		return;
+
+	sk = sock->sk;
+	if (!sk)
+		return;
+
+	napi_id = READ_ONCE(sk->sk_napi_id);
+
+	/* Non-NAPI IDs can be rejected */
+	if (napi_id < MIN_NAPI_ID)
+		return;
+
+	spin_lock(&ctx->napi_lock);
+	list_for_each_entry(ne, &ctx->napi_list, list) {
+		if (ne->napi_id == napi_id) {
+			ne->timeout = jiffies + NAPI_TIMEOUT;
+			goto out;
+		}
+	}
+
+	ne = kmalloc(sizeof(*ne), GFP_NOWAIT);
+	if (!ne)
+		goto out;
+
+	ne->napi_id = napi_id;
+	ne->timeout = jiffies + NAPI_TIMEOUT;
+	list_add_tail(&ne->list, &ctx->napi_list);
+out:
+	spin_unlock(&ctx->napi_lock);
+}
+
+static inline void io_check_napi_entry_timeout(struct napi_entry *ne)
+{
+	if (time_after(jiffies, ne->timeout)) {
+		list_del(&ne->list);
+		kfree(ne);
+	}
+}
+
+/*
+ * Busy poll if globally on and supporting sockets found
+ */
+static bool io_napi_busy_loop(struct list_head *napi_list)
+{
+	struct napi_entry *ne, *n;
+
+	list_for_each_entry_safe(ne, n, napi_list, list) {
+		napi_busy_loop(ne->napi_id, NULL, NULL, true,
+			       BUSY_POLL_BUDGET);
+		io_check_napi_entry_timeout(ne);
+	}
+	return !list_empty(napi_list);
+}
+
+static void io_free_napi_list(struct io_ring_ctx *ctx)
+{
+	spin_lock(&ctx->napi_lock);
+	while (!list_empty(&ctx->napi_list)) {
+		struct napi_entry *ne =
+			list_first_entry(&ctx->napi_list, struct napi_entry,
+					 list);
+
+		list_del(&ne->list);
+		kfree(ne);
+	}
+	spin_unlock(&ctx->napi_lock);
+}
+#else
+static inline void io_add_napi(struct file *file, struct io_ring_ctx *ctx)
+{
+}
+
+static inline void io_free_napi_list(struct io_ring_ctx *ctx)
+{
+}
+#endif /* CONFIG_NET_RX_BUSY_POLL */
+
 struct io_poll_table {
 	struct poll_table_struct pt;
 	struct io_kiocb *req;
@@ -5545,6 +5657,7 @@ static int io_poll_check_events(struct io_kiocb *req)
 			if (unlikely(!filled))
 				return -ECANCELED;
 			io_cqring_ev_posted(ctx);
+			io_add_napi(req->file, ctx);
 		} else if (req->result) {
 			return 0;
 		}
@@ -5777,6 +5890,7 @@ static int __io_arm_poll_handler(struct io_kiocb *req,
 		__io_poll_execute(req, mask);
 		return 0;
 	}
+	io_add_napi(req->file, req->ctx);
 
 	/*
 	 * Release ownership. If someone tried to queue a tw while it was
@@ -7519,7 +7633,11 @@ static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
 		    !(ctx->flags & IORING_SETUP_R_DISABLED))
 			ret = io_submit_sqes(ctx, to_submit);
 		mutex_unlock(&ctx->uring_lock);
-
+#ifdef CONFIG_NET_RX_BUSY_POLL
+		if (!list_empty(&ctx->napi_list) &&
+		    io_napi_busy_loop(&ctx->napi_list))
+			++ret;
+#endif
 		if (to_submit && wq_has_sleeper(&ctx->sqo_sq_wait))
 			wake_up(&ctx->sqo_sq_wait);
 		if (creds)
@@ -7650,6 +7768,9 @@ struct io_wait_queue {
 	struct io_ring_ctx *ctx;
 	unsigned cq_tail;
 	unsigned nr_timeouts;
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	unsigned busy_poll_to;
+#endif
 };
 
 static inline bool io_should_wake(struct io_wait_queue *iowq)
@@ -7711,6 +7832,87 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 	return 1;
 }
 
+#ifdef CONFIG_NET_RX_BUSY_POLL
+static void io_adjust_busy_loop_timeout(struct timespec64 *ts,
+					struct io_wait_queue *iowq)
+{
+	unsigned busy_poll_to = READ_ONCE(sysctl_net_busy_poll);
+	struct timespec64 pollto = ns_to_timespec64(1000 * (s64)busy_poll_to);
+
+	if (timespec64_compare(ts, &pollto) > 0) {
+		*ts = timespec64_sub(*ts, pollto);
+		iowq->busy_poll_to = busy_poll_to;
+	} else {
+		u64 to = timespec64_to_ns(ts);
+
+		do_div(to, 1000);
+		iowq->busy_poll_to = to;
+		ts->tv_sec = 0;
+		ts->tv_nsec = 0;
+	}
+}
+
+static inline bool io_busy_loop_timeout(unsigned long start_time,
+					unsigned long bp_usec)
+{
+	if (bp_usec) {
+		unsigned long end_time = start_time + bp_usec;
+		unsigned long now = busy_loop_current_time();
+
+		return time_after(now, end_time);
+	}
+	return true;
+}
+
+static bool io_busy_loop_end(void *p, unsigned long start_time)
+{
+	struct io_wait_queue *iowq = p;
+
+	return signal_pending(current) ||
+	       io_should_wake(iowq) ||
+	       io_busy_loop_timeout(start_time, iowq->busy_poll_to);
+}
+
+static void io_blocking_napi_busy_loop(struct list_head *napi_list,
+				       struct io_wait_queue *iowq)
+{
+	unsigned long start_time =
+		list_is_singular(napi_list) ? 0 :
+		busy_loop_current_time();
+
+	do {
+		if (list_is_singular(napi_list)) {
+			struct napi_entry *ne =
+				list_first_entry(napi_list,
+						 struct napi_entry, list);
+
+			napi_busy_loop(ne->napi_id, io_busy_loop_end, iowq,
+				       true, BUSY_POLL_BUDGET);
+			io_check_napi_entry_timeout(ne);
+			break;
+		}
+	} while (io_napi_busy_loop(napi_list) &&
+		 !io_busy_loop_end(iowq, start_time));
+}
+
+static void io_putback_napi_list(struct io_ring_ctx *ctx,
+				 struct list_head *napi_list)
+{
+	struct napi_entry *cne, *lne;
+
+	spin_lock(&ctx->napi_lock);
+	list_for_each_entry(cne, &ctx->napi_list, list)
+		list_for_each_entry(lne, napi_list, list)
+			if (cne->napi_id == lne->napi_id) {
+				list_del(&lne->list);
+				kfree(lne);
+				break;
+			}
+	list_splice(napi_list, &ctx->napi_list);
+	spin_unlock(&ctx->napi_lock);
+}
+#endif /* CONFIG_NET_RX_BUSY_POLL */
+
 /*
  * Wait until events become available, if we don't already have some. The
  * application must reap them itself, as they reside on the shared cq ring.
@@ -7723,6 +7925,9 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 	struct io_rings *rings = ctx->rings;
 	ktime_t timeout = KTIME_MAX;
 	int ret;
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	LIST_HEAD(local_napi_list);
+#endif
 
 	do {
 		io_cqring_overflow_flush(ctx);
@@ -7745,13 +7950,29 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 			return ret;
 	}
 
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	iowq.busy_poll_to = 0;
+	if (!(ctx->flags & IORING_SETUP_SQPOLL)) {
+		spin_lock(&ctx->napi_lock);
+		list_splice_init(&ctx->napi_list, &local_napi_list);
+		spin_unlock(&ctx->napi_lock);
+	}
+#endif
 	if (uts) {
 		struct timespec64 ts;
 
 		if (get_timespec64(&ts, uts))
 			return -EFAULT;
+#ifdef CONFIG_NET_RX_BUSY_POLL
+		if (!list_empty(&local_napi_list))
+			io_adjust_busy_loop_timeout(&ts, &iowq);
+#endif
 		timeout = ktime_add_ns(timespec64_to_ktime(ts), ktime_get_ns());
 	}
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	else if (!list_empty(&local_napi_list))
+		iowq.busy_poll_to = READ_ONCE(sysctl_net_busy_poll);
+#endif
 
 	init_waitqueue_func_entry(&iowq.wq, io_wake_function);
 	iowq.wq.private = current;
@@ -7761,6 +7982,12 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 	iowq.cq_tail = READ_ONCE(ctx->rings->cq.head) + min_events;
 
 	trace_io_uring_cqring_wait(ctx, min_events);
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	if (iowq.busy_poll_to)
+		io_blocking_napi_busy_loop(&local_napi_list, &iowq);
+	if (!list_empty(&local_napi_list))
+		io_putback_napi_list(ctx, &local_napi_list);
+#endif
 	do {
 		/* if we can't even flush overflow, don't wait for more */
 		if (!io_cqring_overflow_flush(ctx)) {
@@ -9483,6 +9710,7 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_req_caches_free(ctx);
 	if (ctx->hash_map)
 		io_wq_put_hash(ctx->hash_map);
+	io_free_napi_list(ctx);
 	kfree(ctx->cancel_hash);
 	kfree(ctx->dummy_ubuf);
 	kfree(ctx);
-- 
2.35.1