Add support for a polled io_uring instance. When a read or write is
submitted to a polled io_uring, the application must poll for
completions on the CQ ring through io_uring_enter(2). Polled IO may not
generate IRQ completions, hence they need to be actively found by the
application itself.
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.
Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/io_uring.c | 275 ++++++++++++++++++++++++++++++++--
include/uapi/linux/io_uring.h | 5 +
2 files changed, 271 insertions(+), 9 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index dc9155b7294e..30efe5edf6aa 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -124,6 +124,14 @@ struct io_ring_ctx {
struct {
spinlock_t completion_lock;
+ bool poll_multi_file;
+ /*
+ * ->poll_list is protected by the ctx->uring_lock for
+ * io_uring instances that don't use IORING_SETUP_SQPOLL.
+ * For SQPOLL, only the single threaded io_sq_thread() will
+ * manipulate the list, hence no extra locking is needed there.
+ */
+ struct list_head poll_list;
} ____cacheline_aligned_in_smp;
#if defined(CONFIG_UNIX)
@@ -135,6 +143,7 @@ struct sqe_submit {
const struct io_uring_sqe *sqe;
unsigned short index;
bool has_user;
+ bool needs_lock;
};
struct io_kiocb {
@@ -146,12 +155,15 @@ struct io_kiocb {
struct list_head list;
unsigned int flags;
#define REQ_F_FORCE_NONBLOCK 1 /* inline submission attempt */
+#define REQ_F_IOPOLL_COMPLETED 2 /* polled IO has completed */
u64 user_data;
+ u64 error;
struct work_struct work;
};
#define IO_PLUG_THRESHOLD 2
+#define IO_IOPOLL_BATCH 8
static struct kmem_cache *req_cachep;
@@ -196,6 +208,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
mutex_init(&ctx->uring_lock);
init_waitqueue_head(&ctx->wait);
spin_lock_init(&ctx->completion_lock);
+ INIT_LIST_HEAD(&ctx->poll_list);
return ctx;
}
@@ -297,12 +310,153 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
return NULL;
}
+static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
+{
+ if (*nr) {
+ kmem_cache_free_bulk(req_cachep, *nr, reqs);
+ io_ring_drop_ctx_refs(ctx, *nr);
+ *nr = 0;
+ }
+}
+
static void io_free_req(struct io_kiocb *req)
{
io_ring_drop_ctx_refs(req->ctx, 1);
kmem_cache_free(req_cachep, req);
}
+/*
+ * Find and free completed poll iocbs
+ */
+static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
+ struct list_head *done)
+{
+ void *reqs[IO_IOPOLL_BATCH];
+ struct io_kiocb *req;
+ int to_free = 0;
+
+ while (!list_empty(done)) {
+ req = list_first_entry(done, struct io_kiocb, list);
+ list_del(&req->list);
+
+ io_cqring_fill_event(ctx, req->user_data, req->error, 0);
+
+ reqs[to_free++] = req;
+ (*nr_events)++;
+
+ fput(req->rw.ki_filp);
+ if (to_free == ARRAY_SIZE(reqs))
+ io_free_req_many(ctx, reqs, &to_free);
+ }
+ io_commit_cqring(ctx);
+
+ io_free_req_many(ctx, reqs, &to_free);
+}
+
+static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
+ long min)
+{
+ struct io_kiocb *req, *tmp;
+ LIST_HEAD(done);
+ bool spin;
+ int ret;
+
+ /*
+ * Only spin for completions if we don't have multiple devices hanging
+ * off our complete list, and we're under the requested amount.
+ */
+ spin = !ctx->poll_multi_file && *nr_events < min;
+
+ ret = 0;
+ list_for_each_entry_safe(req, tmp, &ctx->poll_list, list) {
+ struct kiocb *kiocb = &req->rw;
+
+ /*
+ * Move completed entries to our local list. If we find a
+ * request that requires polling, break out and complete
+ * the done list first, if we have entries there.
+ */
+ if (req->flags & REQ_F_IOPOLL_COMPLETED) {
+ list_move_tail(&req->list, &done);
+ continue;
+ }
+ if (!list_empty(&done))
+ break;
+
+ ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
+ if (ret < 0)
+ break;
+
+ if (ret && spin)
+ spin = false;
+ ret = 0;
+ }
+
+ if (!list_empty(&done))
+ io_iopoll_complete(ctx, nr_events, &done);
+
+ return ret;
+}
+
+/*
+ * Poll for a mininum of 'min' events. 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)
+{
+ while (!list_empty(&ctx->poll_list)) {
+ int ret;
+
+ ret = io_do_iopoll(ctx, nr_events, min);
+ if (ret < 0)
+ return ret;
+ if (!min || *nr_events >= min)
+ return 0;
+ }
+
+ return 1;
+}
+
+/*
+ * 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(&ctx->poll_list)) {
+ 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;
+
+ do {
+ 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;
+ } while (min && !*nr_events && !need_resched());
+
+ return ret;
+}
+
static void kiocb_end_write(struct kiocb *kiocb)
{
if (kiocb->ki_flags & IOCB_WRITE) {
@@ -329,6 +483,53 @@ static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
io_free_req(req);
}
+static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
+{
+ struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+
+ kiocb_end_write(kiocb);
+
+ req->error = res;
+ if (res != -EAGAIN)
+ req->flags |= REQ_F_IOPOLL_COMPLETED;
+}
+
+/*
+ * 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_iopoll_getevents() thread before the issuer is done
+ * accessing the kiocb cookie.
+ */
+static void io_iopoll_req_issued(struct io_kiocb *req)
+{
+ struct io_ring_ctx *ctx = req->ctx;
+
+ /*
+ * Track whether we have multiple files in our lists. This will impact
+ * how we do polling eventually, not spinning if we're on potentially
+ * different devices.
+ */
+ if (list_empty(&ctx->poll_list)) {
+ ctx->poll_multi_file = false;
+ } else if (!ctx->poll_multi_file) {
+ struct io_kiocb *list_req;
+
+ list_req = list_first_entry(&ctx->poll_list, struct io_kiocb,
+ list);
+ if (list_req->rw.ki_filp != req->rw.ki_filp)
+ ctx->poll_multi_file = true;
+ }
+
+ /*
+ * For fast devices, IO may have already completed. If it has, add
+ * it to the front so we find it first.
+ */
+ if (req->flags & REQ_F_IOPOLL_COMPLETED)
+ list_add(&req->list, &ctx->poll_list);
+ else
+ list_add_tail(&req->list, &ctx->poll_list);
+}
+
/*
* If we tracked the file through the SCM inflight mechanism, we could support
* any file. For now, just ensure that anything potentially problematic is done
@@ -349,6 +550,7 @@ static bool io_file_supports_async(struct file *file)
static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
bool force_nonblock)
{
+ struct io_ring_ctx *ctx = req->ctx;
struct kiocb *kiocb = &req->rw;
unsigned ioprio;
int fd, ret;
@@ -384,12 +586,22 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
kiocb->ki_flags |= IOCB_NOWAIT;
req->flags |= REQ_F_FORCE_NONBLOCK;
}
- if (kiocb->ki_flags & IOCB_HIPRI) {
- ret = -EINVAL;
- goto out_fput;
- }
+ if (ctx->flags & IORING_SETUP_IOPOLL) {
+ ret = -EOPNOTSUPP;
+ if (!(kiocb->ki_flags & IOCB_DIRECT) ||
+ !kiocb->ki_filp->f_op->iopoll)
+ goto out_fput;
- kiocb->ki_complete = io_complete_rw;
+ req->error = 0;
+ kiocb->ki_flags |= IOCB_HIPRI;
+ kiocb->ki_complete = io_complete_rw_iopoll;
+ } else {
+ if (kiocb->ki_flags & IOCB_HIPRI) {
+ ret = -EINVAL;
+ goto out_fput;
+ }
+ kiocb->ki_complete = io_complete_rw;
+ }
return 0;
out_fput:
fput(kiocb->ki_filp);
@@ -543,6 +755,9 @@ static int io_nop(struct io_kiocb *req, u64 user_data)
struct io_ring_ctx *ctx = req->ctx;
long err = 0;
+ if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
+ return -EINVAL;
+
/*
* Twilight zone - it's possible that someone issued an opcode that
* has a file attached, then got -EAGAIN on submission, and changed
@@ -566,6 +781,8 @@ static int io_prep_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe)
if (req->rw.ki_filp)
return 0;
+ if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+ return -EINVAL;
if (unlikely(sqe->addr || sqe->ioprio))
return -EINVAL;
@@ -637,7 +854,22 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
break;
}
- return ret;
+ if (ret)
+ return ret;
+
+ if (ctx->flags & IORING_SETUP_IOPOLL) {
+ if (req->error == -EAGAIN)
+ return -EAGAIN;
+
+ /* workqueue context doesn't hold uring_lock, grab it now */
+ if (s->needs_lock)
+ mutex_lock(&ctx->uring_lock);
+ io_iopoll_req_issued(req);
+ if (s->needs_lock)
+ mutex_unlock(&ctx->uring_lock);
+ }
+
+ return 0;
}
static void io_sq_wq_submit_work(struct work_struct *work)
@@ -661,8 +893,19 @@ static void io_sq_wq_submit_work(struct work_struct *work)
use_mm(ctx->sqo_mm);
set_fs(USER_DS);
s->has_user = true;
+ s->needs_lock = true;
- ret = __io_submit_sqe(ctx, req, s, false);
+ do {
+ ret = __io_submit_sqe(ctx, req, s, false);
+ /*
+ * We can get EAGAIN for polled IO even though we're forcing
+ * a sync submission from here, since we can't wait for
+ * request slots on the block side.
+ */
+ if (ret != -EAGAIN)
+ break;
+ cond_resched();
+ } while (1);
set_fs(old_fs);
unuse_mm(ctx->sqo_mm);
@@ -793,6 +1036,8 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
break;
s.has_user = true;
+ s.needs_lock = false;
+
ret = io_submit_sqe(ctx, &s);
if (ret) {
io_drop_sqring(ctx);
@@ -938,6 +1183,9 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
destroy_workqueue(ctx->sqo_wq);
if (ctx->sqo_mm)
mmdrop(ctx->sqo_mm);
+
+ io_iopoll_reap_events(ctx);
+
#if defined(CONFIG_UNIX)
if (ctx->ring_sock)
sock_release(ctx->ring_sock);
@@ -984,6 +1232,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
percpu_ref_kill(&ctx->refs);
mutex_unlock(&ctx->uring_lock);
+ io_iopoll_reap_events(ctx);
wait_for_completion(&ctx->ctx_done);
io_ring_ctx_free(ctx);
}
@@ -1064,6 +1313,8 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
goto out_ctx;
}
if (flags & IORING_ENTER_GETEVENTS) {
+ unsigned nr_events = 0;
+
/*
* The application could have included the 'to_submit' count
* in how many events it wanted to wait for. If we failed to
@@ -1073,7 +1324,13 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
if (submitted < to_submit)
min_complete = min_t(unsigned, submitted, min_complete);
- ret = io_cqring_wait(ctx, min_complete, sig, sigsz);
+ if (ctx->flags & IORING_SETUP_IOPOLL) {
+ mutex_lock(&ctx->uring_lock);
+ ret = io_iopoll_check(ctx, &nr_events, min_complete);
+ mutex_unlock(&ctx->uring_lock);
+ } else {
+ ret = io_cqring_wait(ctx, min_complete, sig, sigsz);
+ }
}
out_ctx:
@@ -1270,7 +1527,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
return -EINVAL;
}
- if (p.flags)
+ if (p.flags & ~IORING_SETUP_IOPOLL)
return -EINVAL;
ret = io_uring_create(entries, &p);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 4589d56d0b68..5c457ea396e6 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -30,6 +30,11 @@ struct io_uring_sqe {
__u64 __pad2[3];
};
+/*
+ * io_uring_setup() flags
+ */
+#define IORING_SETUP_IOPOLL (1U << 0) /* io_context is polled */
+
#define IORING_OP_NOP 0
#define IORING_OP_READV 1
#define IORING_OP_WRITEV 2
--
2.17.1
