#include "block/raw-aio.h"
#include "qemu/event_notifier.h"
#include "qemu/coroutine.h"
+#include "qapi/error.h"
#include <libaio.h>
*/
#define MAX_EVENTS 128
-#define MAX_QUEUED_IO 128
-
struct qemu_laiocb {
BlockAIOCB common;
Coroutine *co;
typedef struct {
int plugged;
- unsigned int n;
+ unsigned int in_queue;
+ unsigned int in_flight;
bool blocked;
QSIMPLEQ_HEAD(, qemu_laiocb) pending;
} LaioQueue;
struct LinuxAioState {
+ AioContext *aio_context;
+
io_context_t ctx;
EventNotifier e;
- /* io queue for submit at batch */
+ /* io queue for submit at batch. Protected by AioContext lock. */
LaioQueue io_q;
- /* I/O completion processing */
+ /* I/O completion processing. Only runs in I/O thread. */
QEMUBH *completion_bh;
- struct io_event events[MAX_EVENTS];
int event_idx;
int event_max;
};
laiocb->ret = ret;
if (laiocb->co) {
- qemu_coroutine_enter(laiocb->co, NULL);
+ /* If the coroutine is already entered it must be in ioq_submit() and
+ * will notice laio->ret has been filled in when it eventually runs
+ * later. Coroutines cannot be entered recursively so avoid doing
+ * that!
+ */
+ if (!qemu_coroutine_entered(laiocb->co)) {
+ aio_co_wake(laiocb->co);
+ }
} else {
laiocb->common.cb(laiocb->common.opaque, ret);
qemu_aio_unref(laiocb);
}
}
-/* The completion BH fetches completed I/O requests and invokes their
- * callbacks.
+/**
+ * aio_ring buffer which is shared between userspace and kernel.
*
- * The function is somewhat tricky because it supports nested event loops, for
- * example when a request callback invokes aio_poll(). In order to do this,
- * the completion events array and index are kept in LinuxAioState. The BH
- * reschedules itself as long as there are completions pending so it will
- * either be called again in a nested event loop or will be called after all
- * events have been completed. When there are no events left to complete, the
- * BH returns without rescheduling.
+ * This copied from linux/fs/aio.c, common header does not exist
+ * but AIO exists for ages so we assume ABI is stable.
*/
-static void qemu_laio_completion_bh(void *opaque)
+struct aio_ring {
+ unsigned id; /* kernel internal index number */
+ unsigned nr; /* number of io_events */
+ unsigned head; /* Written to by userland or by kernel. */
+ unsigned tail;
+
+ unsigned magic;
+ unsigned compat_features;
+ unsigned incompat_features;
+ unsigned header_length; /* size of aio_ring */
+
+ struct io_event io_events[0];
+};
+
+/**
+ * io_getevents_peek:
+ * @ctx: AIO context
+ * @events: pointer on events array, output value
+
+ * Returns the number of completed events and sets a pointer
+ * on events array. This function does not update the internal
+ * ring buffer, only reads head and tail. When @events has been
+ * processed io_getevents_commit() must be called.
+ */
+static inline unsigned int io_getevents_peek(io_context_t ctx,
+ struct io_event **events)
{
- LinuxAioState *s = opaque;
+ struct aio_ring *ring = (struct aio_ring *)ctx;
+ unsigned int head = ring->head, tail = ring->tail;
+ unsigned int nr;
- /* Fetch more completion events when empty */
- if (s->event_idx == s->event_max) {
- do {
- struct timespec ts = { 0 };
- s->event_max = io_getevents(s->ctx, MAX_EVENTS, MAX_EVENTS,
- s->events, &ts);
- } while (s->event_max == -EINTR);
-
- s->event_idx = 0;
- if (s->event_max <= 0) {
- s->event_max = 0;
- return; /* no more events */
- }
+ nr = tail >= head ? tail - head : ring->nr - head;
+ *events = ring->io_events + head;
+ /* To avoid speculative loads of s->events[i] before observing tail.
+ Paired with smp_wmb() inside linux/fs/aio.c: aio_complete(). */
+ smp_rmb();
+
+ return nr;
+}
+
+/**
+ * io_getevents_commit:
+ * @ctx: AIO context
+ * @nr: the number of events on which head should be advanced
+ *
+ * Advances head of a ring buffer.
+ */
+static inline void io_getevents_commit(io_context_t ctx, unsigned int nr)
+{
+ struct aio_ring *ring = (struct aio_ring *)ctx;
+
+ if (nr) {
+ ring->head = (ring->head + nr) % ring->nr;
}
+}
+
+/**
+ * io_getevents_advance_and_peek:
+ * @ctx: AIO context
+ * @events: pointer on events array, output value
+ * @nr: the number of events on which head should be advanced
+ *
+ * Advances head of a ring buffer and returns number of elements left.
+ */
+static inline unsigned int
+io_getevents_advance_and_peek(io_context_t ctx,
+ struct io_event **events,
+ unsigned int nr)
+{
+ io_getevents_commit(ctx, nr);
+ return io_getevents_peek(ctx, events);
+}
+
+/**
+ * qemu_laio_process_completions:
+ * @s: AIO state
+ *
+ * Fetches completed I/O requests and invokes their callbacks.
+ *
+ * The function is somewhat tricky because it supports nested event loops, for
+ * example when a request callback invokes aio_poll(). In order to do this,
+ * indices are kept in LinuxAioState. Function schedules BH completion so it
+ * can be called again in a nested event loop. When there are no events left
+ * to complete the BH is being canceled.
+ */
+static void qemu_laio_process_completions(LinuxAioState *s)
+{
+ struct io_event *events;
/* Reschedule so nested event loops see currently pending completions */
qemu_bh_schedule(s->completion_bh);
- /* Process completion events */
- while (s->event_idx < s->event_max) {
- struct iocb *iocb = s->events[s->event_idx].obj;
- struct qemu_laiocb *laiocb =
+ while ((s->event_max = io_getevents_advance_and_peek(s->ctx, &events,
+ s->event_idx))) {
+ for (s->event_idx = 0; s->event_idx < s->event_max; ) {
+ struct iocb *iocb = events[s->event_idx].obj;
+ struct qemu_laiocb *laiocb =
container_of(iocb, struct qemu_laiocb, iocb);
- laiocb->ret = io_event_ret(&s->events[s->event_idx]);
- s->event_idx++;
+ laiocb->ret = io_event_ret(&events[s->event_idx]);
- qemu_laio_process_completion(laiocb);
+ /* Change counters one-by-one because we can be nested. */
+ s->io_q.in_flight--;
+ s->event_idx++;
+ qemu_laio_process_completion(laiocb);
+ }
}
+ qemu_bh_cancel(s->completion_bh);
+
+ /* If we are nested we have to notify the level above that we are done
+ * by setting event_max to zero, upper level will then jump out of it's
+ * own `for` loop. If we are the last all counters droped to zero. */
+ s->event_max = 0;
+ s->event_idx = 0;
+}
+
+static void qemu_laio_process_completions_and_submit(LinuxAioState *s)
+{
+ aio_context_acquire(s->aio_context);
+ qemu_laio_process_completions(s);
+
if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
ioq_submit(s);
}
+ aio_context_release(s->aio_context);
+}
- qemu_bh_cancel(s->completion_bh);
+static void qemu_laio_completion_bh(void *opaque)
+{
+ LinuxAioState *s = opaque;
+
+ qemu_laio_process_completions_and_submit(s);
}
static void qemu_laio_completion_cb(EventNotifier *e)
LinuxAioState *s = container_of(e, LinuxAioState, e);
if (event_notifier_test_and_clear(&s->e)) {
- qemu_laio_completion_bh(s);
+ qemu_laio_process_completions_and_submit(s);
+ }
+}
+
+static bool qemu_laio_poll_cb(void *opaque)
+{
+ EventNotifier *e = opaque;
+ LinuxAioState *s = container_of(e, LinuxAioState, e);
+ struct io_event *events;
+
+ if (!io_getevents_peek(s->ctx, &events)) {
+ return false;
}
+
+ qemu_laio_process_completions_and_submit(s);
+ return true;
}
static void laio_cancel(BlockAIOCB *blockacb)
{
QSIMPLEQ_INIT(&io_q->pending);
io_q->plugged = 0;
- io_q->n = 0;
+ io_q->in_queue = 0;
+ io_q->in_flight = 0;
io_q->blocked = false;
}
{
int ret, len;
struct qemu_laiocb *aiocb;
- struct iocb *iocbs[MAX_QUEUED_IO];
+ struct iocb *iocbs[MAX_EVENTS];
QSIMPLEQ_HEAD(, qemu_laiocb) completed;
do {
+ if (s->io_q.in_flight >= MAX_EVENTS) {
+ break;
+ }
len = 0;
QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
iocbs[len++] = &aiocb->iocb;
- if (len == MAX_QUEUED_IO) {
+ if (s->io_q.in_flight + len >= MAX_EVENTS) {
break;
}
}
break;
}
if (ret < 0) {
- abort();
+ /* Fail the first request, retry the rest */
+ aiocb = QSIMPLEQ_FIRST(&s->io_q.pending);
+ QSIMPLEQ_REMOVE_HEAD(&s->io_q.pending, next);
+ s->io_q.in_queue--;
+ aiocb->ret = ret;
+ qemu_laio_process_completion(aiocb);
+ continue;
}
- s->io_q.n -= ret;
+ s->io_q.in_flight += ret;
+ s->io_q.in_queue -= ret;
aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
} while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
- s->io_q.blocked = (s->io_q.n > 0);
+ s->io_q.blocked = (s->io_q.in_queue > 0);
+
+ if (s->io_q.in_flight) {
+ /* We can try to complete something just right away if there are
+ * still requests in-flight. */
+ qemu_laio_process_completions(s);
+ /*
+ * Even we have completed everything (in_flight == 0), the queue can
+ * have still pended requests (in_queue > 0). We do not attempt to
+ * repeat submission to avoid IO hang. The reason is simple: s->e is
+ * still set and completion callback will be called shortly and all
+ * pended requests will be submitted from there.
+ */
+ }
}
void laio_io_plug(BlockDriverState *bs, LinuxAioState *s)
{
- assert(!s->io_q.plugged);
- s->io_q.plugged = 1;
+ s->io_q.plugged++;
}
void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s)
{
assert(s->io_q.plugged);
- s->io_q.plugged = 0;
- if (!s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
+ if (--s->io_q.plugged == 0 &&
+ !s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
ioq_submit(s);
}
}
io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
- s->io_q.n++;
+ s->io_q.in_queue++;
if (!s->io_q.blocked &&
- (!s->io_q.plugged || s->io_q.n >= MAX_QUEUED_IO)) {
+ (!s->io_q.plugged ||
+ s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) {
ioq_submit(s);
}
.co = qemu_coroutine_self(),
.nbytes = qiov->size,
.ctx = s,
+ .ret = -EINPROGRESS,
.is_read = (type == QEMU_AIO_READ),
.qiov = qiov,
};
return ret;
}
- qemu_coroutine_yield();
+ if (laiocb.ret == -EINPROGRESS) {
+ qemu_coroutine_yield();
+ }
return laiocb.ret;
}
void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context)
{
- aio_set_event_notifier(old_context, &s->e, false, NULL);
+ aio_set_event_notifier(old_context, &s->e, false, NULL, NULL);
qemu_bh_delete(s->completion_bh);
+ s->aio_context = NULL;
}
void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
{
+ s->aio_context = new_context;
s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
aio_set_event_notifier(new_context, &s->e, false,
- qemu_laio_completion_cb);
+ qemu_laio_completion_cb,
+ qemu_laio_poll_cb);
}
-LinuxAioState *laio_init(void)
+LinuxAioState *laio_init(Error **errp)
{
+ int rc;
LinuxAioState *s;
s = g_malloc0(sizeof(*s));
- if (event_notifier_init(&s->e, false) < 0) {
+ rc = event_notifier_init(&s->e, false);
+ if (rc < 0) {
+ error_setg_errno(errp, -rc, "failed to to initialize event notifier");
goto out_free_state;
}
- if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
+ rc = io_setup(MAX_EVENTS, &s->ctx);
+ if (rc < 0) {
+ error_setg_errno(errp, -rc, "failed to create linux AIO context");
goto out_close_efd;
}
projects / qemu.git / blobdiff