Add support for polled read and write commands. These act like their
non-polled counterparts, except we expect to poll for completion of
them.
To use polling, io_uring_setup() must be used with the
IORING_SETUP_IOPOLL flag being set. It is illegal to mix and match
polled and non-polled IO on an io_uring.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/io_uring.c | 247 ++++++++++++++++++++++++++++++++--
include/uapi/linux/io_uring.h | 5 +
2 files changed, 239 insertions(+), 13 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0bad563f3486..c872bfb32a03 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -71,13 +71,17 @@ struct io_ring_ctx {
struct completion ctx_done;
+ /* iopoll submission state */
struct {
- struct mutex uring_lock;
- wait_queue_head_t wait;
+ spinlock_t poll_lock;
+ struct list_head poll_submitted;
} ____cacheline_aligned_in_smp;
struct {
+ struct list_head poll_completing;
spinlock_t completion_lock;
+ struct mutex uring_lock;
+ wait_queue_head_t wait;
} ____cacheline_aligned_in_smp;
};
@@ -97,9 +101,12 @@ struct io_kiocb {
unsigned long ki_index;
struct list_head ki_list;
unsigned long ki_flags;
+#define KIOCB_F_IOPOLL_COMPLETED 0 /* polled IO has completed */
+#define KIOCB_F_IOPOLL_EAGAIN 1 /* submission got EAGAIN */
};
#define IO_PLUG_THRESHOLD 2
+#define IO_IOPOLL_BATCH 8
struct sqe_submit {
const struct io_uring_sqe *sqe;
@@ -136,6 +143,9 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
spin_lock_init(&ctx->completion_lock);
init_waitqueue_head(&ctx->wait);
+ spin_lock_init(&ctx->poll_lock);
+ INIT_LIST_HEAD(&ctx->poll_submitted);
+ INIT_LIST_HEAD(&ctx->poll_completing);
mutex_init(&ctx->uring_lock);
return ctx;
@@ -187,12 +197,151 @@ static void io_ring_drop_ctx_ref(struct io_ring_ctx *ctx, unsigned refs)
wake_up(&ctx->wait);
}
+static void io_free_kiocb_many(struct io_ring_ctx *ctx, void **iocbs, int *nr)
+{
+ if (*nr) {
+ kmem_cache_free_bulk(kiocb_cachep, *nr, iocbs);
+ io_ring_drop_ctx_ref(ctx, *nr);
+ *nr = 0;
+ }
+}
+
static void io_free_kiocb(struct io_kiocb *iocb)
{
kmem_cache_free(kiocb_cachep, iocb);
io_ring_drop_ctx_ref(iocb->ki_ctx, 1);
}
+/*
+ * Find and free completed poll iocbs
+ */
+static void io_iopoll_reap(struct io_ring_ctx *ctx, unsigned int *nr_events)
+{
+ void *iocbs[IO_IOPOLL_BATCH];
+ struct io_kiocb *iocb, *n;
+ int to_free = 0;
+
+ list_for_each_entry_safe(iocb, n, &ctx->poll_completing, ki_list) {
+ if (!test_bit(KIOCB_F_IOPOLL_COMPLETED, &iocb->ki_flags))
+ continue;
+ if (to_free == ARRAY_SIZE(iocbs))
+ io_free_kiocb_many(ctx, iocbs, &to_free);
+
+ list_del(&iocb->ki_list);
+ iocbs[to_free++] = iocb;
+
+ fput(iocb->rw.ki_filp);
+ (*nr_events)++;
+ }
+
+ if (to_free)
+ io_free_kiocb_many(ctx, iocbs, &to_free);
+}
+
+/*
+ * Poll for a mininum of 'min' events, and a maximum of 'max'. Note that if
+ * min == 0 we consider that a non-spinning poll check - we'll still enter
+ * the driver poll loop, but only as a non-spinning completion check.
+ */
+static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
+ long min)
+{
+ struct io_kiocb *iocb;
+ int found, polled, ret;
+
+ /*
+ * Check if we already have done events that satisfy what we need
+ */
+ if (!list_empty(&ctx->poll_completing)) {
+ io_iopoll_reap(ctx, nr_events);
+ if (min && *nr_events >= min)
+ return 0;
+ }
+
+ /*
+ * Take in a new working set from the submitted list, if possible.
+ */
+ if (!list_empty_careful(&ctx->poll_submitted)) {
+ spin_lock(&ctx->poll_lock);
+ list_splice_init(&ctx->poll_submitted, &ctx->poll_completing);
+ spin_unlock(&ctx->poll_lock);
+ }
+
+ if (list_empty(&ctx->poll_completing))
+ return 0;
+
+ /*
+ * Check again now that we have a new batch.
+ */
+ io_iopoll_reap(ctx, nr_events);
+ if (min && *nr_events >= min)
+ return 0;
+
+ polled = found = 0;
+ list_for_each_entry(iocb, &ctx->poll_completing, ki_list) {
+ /*
+ * Poll for needed events with spin == true, anything after
+ * that we just check if we have more, up to max.
+ */
+ bool spin = !polled || *nr_events < min;
+ struct kiocb *kiocb = &iocb->rw;
+
+ if (test_bit(KIOCB_F_IOPOLL_COMPLETED, &iocb->ki_flags))
+ break;
+
+ found++;
+ ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
+ if (ret < 0)
+ return ret;
+
+ polled += ret;
+ }
+
+ io_iopoll_reap(ctx, nr_events);
+ if (*nr_events >= min)
+ return 0;
+ return found;
+}
+
+/*
+ * We can't just wait for polled events to come to us, we have to actively
+ * find and complete them.
+ */
+static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
+{
+ if (!(ctx->flags & IORING_SETUP_IOPOLL))
+ return;
+
+ mutex_lock(&ctx->uring_lock);
+ while (!list_empty_careful(&ctx->poll_submitted) ||
+ !list_empty(&ctx->poll_completing)) {
+ unsigned int nr_events = 0;
+
+ io_iopoll_getevents(ctx, &nr_events, 1);
+ }
+ mutex_unlock(&ctx->uring_lock);
+}
+
+static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
+ long min)
+{
+ int ret = 0;
+
+ while (!*nr_events || !need_resched()) {
+ int tmin = 0;
+
+ if (*nr_events < min)
+ tmin = min - *nr_events;
+
+ ret = io_iopoll_getevents(ctx, nr_events, tmin);
+ if (ret <= 0)
+ break;
+ ret = 0;
+ }
+
+ return ret;
+}
+
static void kiocb_end_write(struct kiocb *kiocb)
{
if (kiocb->ki_flags & IOCB_WRITE) {
@@ -208,18 +357,16 @@ static void kiocb_end_write(struct kiocb *kiocb)
}
}
-static void io_cqring_fill_event(struct io_ring_ctx *ctx, unsigned ki_index,
- long res, unsigned ev_flags)
+static void __io_cqring_fill_event(struct io_ring_ctx *ctx, unsigned ki_index,
+ long res, unsigned ev_flags)
{
struct io_uring_cqe *cqe;
- unsigned long flags;
/*
* If we can't get a cq entry, userspace overflowed the
* submission (by quite a lot). Increment the overflow count in
* the ring.
*/
- spin_lock_irqsave(&ctx->completion_lock, flags);
cqe = io_peek_cqring(ctx);
if (cqe) {
cqe->index = ki_index;
@@ -229,6 +376,15 @@ static void io_cqring_fill_event(struct io_ring_ctx *ctx, unsigned ki_index,
io_inc_cqring(ctx);
} else
ctx->cq_ring->overflow++;
+}
+
+static void io_cqring_fill_event(struct io_ring_ctx *ctx, unsigned ki_index,
+ long res, unsigned ev_flags)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&ctx->completion_lock, flags);
+ __io_cqring_fill_event(ctx, ki_index, res, ev_flags);
spin_unlock_irqrestore(&ctx->completion_lock, flags);
}
@@ -243,8 +399,23 @@ static void io_complete_scqring_rw(struct kiocb *kiocb, long res, long res2)
io_free_kiocb(iocb);
}
+static void io_complete_scqring_iopoll(struct kiocb *kiocb, long res, long res2)
+{
+ struct io_kiocb *iocb = container_of(kiocb, struct io_kiocb, rw);
+
+ kiocb_end_write(kiocb);
+
+ if (unlikely(res == -EAGAIN)) {
+ set_bit(KIOCB_F_IOPOLL_EAGAIN, &iocb->ki_flags);
+ } else {
+ __io_cqring_fill_event(iocb->ki_ctx, iocb->ki_index, res, 0);
+ set_bit(KIOCB_F_IOPOLL_COMPLETED, &iocb->ki_flags);
+ }
+}
+
static int io_prep_rw(struct io_kiocb *kiocb, const struct io_uring_sqe *sqe)
{
+ struct io_ring_ctx *ctx = kiocb->ki_ctx;
struct kiocb *req = &kiocb->rw;
int ret;
@@ -266,12 +437,22 @@ static int io_prep_rw(struct io_kiocb *kiocb, const struct io_uring_sqe *sqe)
ret = kiocb_set_rw_flags(req, sqe->rw_flags);
if (unlikely(ret))
goto out_fput;
- if (req->ki_flags & IOCB_HIPRI) {
- ret = -EINVAL;
- goto out_fput;
- }
- req->ki_complete = io_complete_scqring_rw;
+ if (ctx->flags & IORING_SETUP_IOPOLL) {
+ ret = -EOPNOTSUPP;
+ if (!(req->ki_flags & IOCB_DIRECT) ||
+ !req->ki_filp->f_op->iopoll)
+ goto out_fput;
+
+ req->ki_flags |= IOCB_HIPRI;
+ req->ki_complete = io_complete_scqring_iopoll;
+ } else {
+ if (req->ki_flags & IOCB_HIPRI) {
+ ret = -EINVAL;
+ goto out_fput;
+ }
+ req->ki_complete = io_complete_scqring_rw;
+ }
return 0;
out_fput:
fput(req->ki_filp);
@@ -298,6 +479,30 @@ static inline void io_rw_done(struct kiocb *req, ssize_t ret)
}
}
+/*
+ * After the iocb has been issued, it's safe to be found on the poll list.
+ * Adding the kiocb to the list AFTER submission ensures that we don't
+ * find it from a io_getevents() thread before the issuer is done accessing
+ * the kiocb cookie.
+ */
+static void io_iopoll_kiocb_issued(struct io_kiocb *kiocb)
+{
+ /*
+ * For fast devices, IO may have already completed. If it has, add
+ * it to the front so we find it first. We can't add to the poll_done
+ * list as that's unlocked from the completion side.
+ */
+ const int front = test_bit(KIOCB_F_IOPOLL_COMPLETED, &kiocb->ki_flags);
+ struct io_ring_ctx *ctx = kiocb->ki_ctx;
+
+ spin_lock(&ctx->poll_lock);
+ if (front)
+ list_add(&kiocb->ki_list, &ctx->poll_submitted);
+ else
+ list_add_tail(&kiocb->ki_list, &ctx->poll_submitted);
+ spin_unlock(&ctx->poll_lock);
+}
+
static ssize_t io_read(struct io_kiocb *kiocb, const struct io_uring_sqe *sqe)
{
struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
@@ -400,6 +605,8 @@ static int io_fsync(struct io_kiocb *kiocb, const struct io_uring_sqe *sqe,
{
struct fsync_iocb *req = &kiocb->fsync;
+ if (kiocb->ki_ctx->flags & IORING_SETUP_IOPOLL)
+ return -EINVAL;
if (unlikely(sqe->addr || sqe->off || sqe->len || sqe->__resv))
return -EINVAL;
@@ -461,6 +668,13 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
*/
if (ret)
goto out_put_req;
+ if (ctx->flags & IORING_SETUP_IOPOLL) {
+ if (test_bit(KIOCB_F_IOPOLL_EAGAIN, &req->ki_flags)) {
+ ret = -EAGAIN;
+ goto out_put_req;
+ }
+ io_iopoll_kiocb_issued(req);
+ }
return 0;
out_put_req:
io_free_kiocb(req);
@@ -573,12 +787,17 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
return ret;
}
if (flags & IORING_ENTER_GETEVENTS) {
+ unsigned nr_events = 0;
int get_ret;
if (!ret && to_submit)
min_complete = 0;
- get_ret = io_cqring_wait(ctx, min_complete);
+ if (ctx->flags & IORING_SETUP_IOPOLL)
+ get_ret = io_iopoll_check(ctx, &nr_events,
+ min_complete);
+ else
+ get_ret = io_cqring_wait(ctx, min_complete);
if (get_ret < 0 && !ret)
ret = get_ret;
}
@@ -604,6 +823,7 @@ static void io_free_scq_urings(struct io_ring_ctx *ctx)
static void io_ring_ctx_free(struct io_ring_ctx *ctx)
{
+ io_iopoll_reap_events(ctx);
io_free_scq_urings(ctx);
percpu_ref_exit(&ctx->refs);
kfree(ctx);
@@ -612,6 +832,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
{
percpu_ref_kill(&ctx->refs);
+ io_iopoll_reap_events(ctx);
wait_for_completion(&ctx->ctx_done);
io_ring_ctx_free(ctx);
}
@@ -815,7 +1036,7 @@ SYSCALL_DEFINE3(io_uring_setup, u32, entries, struct iovec __user *, iovecs,
return -EINVAL;
}
- if (p.flags)
+ if (p.flags & ~IORING_SETUP_IOPOLL)
return -EINVAL;
if (iovecs)
return -EINVAL;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index ae30ed41965f..ba9e5b851f73 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -31,6 +31,11 @@ struct io_uring_sqe {
};
};
+/*
+ * io_uring_setup() flags
+ */
+#define IORING_SETUP_IOPOLL (1 << 0) /* io_context is polled */
+
#define IORING_OP_READV 1
#define IORING_OP_WRITEV 2
#define IORING_OP_FSYNC 3
--
2.17.1
