[Qemu-devel] [PATCH v2 1/5] linux-aio: queue requests that cannot be submitted

[Paolo Bonzini <pbonzini@redhat.com>]

Keep a queue of requests that were not submitted; pass them to
the kernel when a completion is reported, unless the queue is
plugged.

The array of iocbs is rebuilt every time from scratch.  This
avoids keeping the iocbs array and list synchronized.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/linux-aio.c | 75 ++++++++++++++++++++++++-------------------------------
 1 file changed, 33 insertions(+), 42 deletions(-)

diff --git a/block/linux-aio.c b/block/linux-aio.c
index d92513b..b6fbfd8 100644
--- a/block/linux-aio.c
+++ b/block/linux-aio.c
@@ -35,14 +35,13 @@ struct qemu_laiocb {
     size_t nbytes;
     QEMUIOVector *qiov;
     bool is_read;
-    QLIST_ENTRY(qemu_laiocb) node;
+    QSIMPLEQ_ENTRY(qemu_laiocb) next;
 };
 
 typedef struct {
-    struct iocb *iocbs[MAX_QUEUED_IO];
     int plugged;
-    unsigned int size;
     unsigned int idx;
+    QSIMPLEQ_HEAD(, qemu_laiocb) pending;
 } LaioQueue;
 
 struct qemu_laio_state {
@@ -59,6 +58,8 @@ struct qemu_laio_state {
     int event_max;
 };
 
+static int ioq_submit(struct qemu_laio_state *s);
+
 static inline ssize_t io_event_ret(struct io_event *ev)
 {
     return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res);
@@ -135,6 +136,10 @@ static void qemu_laio_completion_bh(void *opaque)
 
         qemu_laio_process_completion(s, laiocb);
     }
+
+    if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
+        ioq_submit(s);
+    }
 }
 
 static void qemu_laio_completion_cb(EventNotifier *e)
@@ -172,52 +177,40 @@ static const AIOCBInfo laio_aiocb_info = {
 
 static void ioq_init(LaioQueue *io_q)
 {
-    io_q->size = MAX_QUEUED_IO;
-    io_q->idx = 0;
+    QSIMPLEQ_INIT(&io_q->pending);
     io_q->plugged = 0;
+    io_q->idx = 0;
 }
 
 static int ioq_submit(struct qemu_laio_state *s)
 {
-    int ret, i = 0;
-    int len = s->io_q.idx;
-
-    do {
-        ret = io_submit(s->ctx, len, s->io_q.iocbs);
-    } while (i++ < 3 && ret == -EAGAIN);
+    int ret, i;
+    int len = 0;
+    struct qemu_laiocb *aiocb;
+    struct iocb *iocbs[MAX_QUEUED_IO];
 
-    /* empty io queue */
-    s->io_q.idx = 0;
+    QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
+        iocbs[len++] = &aiocb->iocb;
+        if (len == MAX_QUEUED_IO) {
+            break;
+        }
+    }
 
+    ret = io_submit(s->ctx, len, iocbs);
+    if (ret == -EAGAIN) {
+        ret = 0;
+    }
     if (ret < 0) {
-        i = 0;
-    } else {
-        i = ret;
+        abort();
     }
 
-    for (; i < len; i++) {
-        struct qemu_laiocb *laiocb =
-            container_of(s->io_q.iocbs[i], struct qemu_laiocb, iocb);
-
-        laiocb->ret = (ret < 0) ? ret : -EIO;
-        qemu_laio_process_completion(s, laiocb);
+    for (i = 0; i < ret; i++) {
+        s->io_q.idx--;
+        QSIMPLEQ_REMOVE_HEAD(&s->io_q.pending, next);
     }
     return ret;
 }
 
-static void ioq_enqueue(struct qemu_laio_state *s, struct iocb *iocb)
-{
-    unsigned int idx = s->io_q.idx;
-
-    s->io_q.iocbs[idx++] = iocb;
-    s->io_q.idx = idx;
-
-    /* submit immediately if queue is full */
-    if (idx == s->io_q.size) {
-        ioq_submit(s);
-    }
-}
-
 void laio_io_plug(BlockDriverState *bs, void *aio_ctx)
 {
     struct qemu_laio_state *s = aio_ctx;
@@ -236,7 +229,7 @@ int laio_io_unplug(BlockDriverState *bs, void *aio_ctx, bool unplug)
         return 0;
     }
 
-    if (s->io_q.idx > 0) {
+    if (!QSIMPLEQ_EMPTY(&s->io_q.pending)) {
         ret = ioq_submit(s);
     }
 
@@ -276,12 +269,10 @@ BlockAIOCB *laio_submit(BlockDriverState *bs, void *aio_ctx, int fd,
     }
     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
 
-    if (!s->io_q.plugged) {
-        if (io_submit(s->ctx, 1, &iocbs) < 0) {
-            goto out_free_aiocb;
-        }
-    } else {
-        ioq_enqueue(s, iocbs);
+    QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
+    s->io_q.idx++;
+    if (s->io_q.idx == (s->io_q.plugged ? MAX_QUEUED_IO : 1)) {
+        ioq_submit(s);
     }
     return &laiocb->common;
 
-- 
2.1.0