Re: [Qemu-devel] [PATCH v3 1/3] linux-aio: fix submit aio as a batch

[Paolo Bonzini <pbonzini@redhat.com>]

> @@ -137,6 +145,12 @@ static void qemu_laio_completion_bh(void *opaque)
>      }
>  }
>  
> +static void qemu_laio_start_retry(struct qemu_laio_state *s)
> +{
> +    if (s->io_q.idx)
> +        qemu_bh_schedule(s->io_q.retry);
> +}
> +
>  static void qemu_laio_completion_cb(EventNotifier *e)
>  {
>      struct qemu_laio_state *s = container_of(e, struct qemu_laio_state, e);
> @@ -144,6 +158,7 @@ static void qemu_laio_completion_cb(EventNotifier *e)
>      if (event_notifier_test_and_clear(&s->e)) {
>          qemu_bh_schedule(s->completion_bh);
>      }
> +    qemu_laio_start_retry(s);

I think you do not even need two bottom halves.  Just call ioq_submit
from completion_bh instead, after the call to io_getevents.

>  }
>  
>  static void laio_cancel(BlockAIOCB *blockacb)
> @@ -163,6 +178,9 @@ static void laio_cancel(BlockAIOCB *blockacb)
>      }
>  
>      laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
> +
> +    /* check if there are requests in io queue */
> +    qemu_laio_start_retry(laiocb->ctx);
>  }
>  
>  static const AIOCBInfo laio_aiocb_info = {
> @@ -177,45 +195,80 @@ static void ioq_init(LaioQueue *io_q)
>      io_q->plugged = 0;
>  }
>  
> -static int ioq_submit(struct qemu_laio_state *s)
> +static void abort_queue(struct qemu_laio_state *s)
> +{
> +    int i;
> +    for (i = 0; i < s->io_q.idx; i++) {
> +        struct qemu_laiocb *laiocb = container_of(s->io_q.iocbs[i],
> +                                                  struct qemu_laiocb,
> +                                                  iocb);
> +        laiocb->ret = -EIO;
> +        qemu_laio_process_completion(s, laiocb);
> +    }
> +}
> +
> +static int ioq_submit(struct qemu_laio_state *s, bool enqueue)
>  {
>      int ret, i = 0;
>      int len = s->io_q.idx;
> +    int j = 0;
>  
> -    do {
> -        ret = io_submit(s->ctx, len, s->io_q.iocbs);
> -    } while (i++ < 3 && ret == -EAGAIN);
> +    if (!len) {
> +        return 0;
> +    }
>  
> -    /* empty io queue */
> -    s->io_q.idx = 0;
> +    ret = io_submit(s->ctx, len, s->io_q.iocbs);
> +    if (ret == -EAGAIN) { /* retry in following completion cb */
> +        return 0;
> +    } else if (ret < 0) {
> +        if (enqueue) {
> +            return ret;
> +        }
>  
> -    if (ret < 0) {
> -        i = 0;
> -    } else {
> -        i = ret;
> +        /* in non-queue path, all IOs have to be completed */
> +        abort_queue(s);
> +        ret = len;
> +    } else if (ret == 0) {
> +        goto out;

No need for goto; just move the "for" loop inside this conditional.  Or
better, just use memmove.  That is:

    if (ret < 0) {
        if (ret == -EAGAIN) {
            return 0;
        }
        if (enqueue) {
            return ret;
        }

        abort_queue(s);
        ret = len;
    }

    if (ret > 0) {
        memmove(...)
        s->io_q.idx -= ret;
    }
    return ret;

> +     * update io queue, for partial completion, retry will be
> +     * started automatically in following completion cb.
> +     */
> +    s->io_q.idx -= ret;
> +
>      return ret;
>  }
>  
> -static void ioq_enqueue(struct qemu_laio_state *s, struct iocb *iocb)
> +static void ioq_submit_retry(void *opaque)
> +{
> +    struct qemu_laio_state *s = opaque;
> +    ioq_submit(s, false);
> +}
> +
> +static int ioq_enqueue(struct qemu_laio_state *s, struct iocb *iocb)
>  {
>      unsigned int idx = s->io_q.idx;
>  
> +    if (unlikely(idx == s->io_q.size)) {
> +        return -1;

return -EAGAIN?

Thanks,

Paolo

> +    }
> +
>      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);
> +    /* submit immediately if queue depth is above 2/3 */
> +    if (idx > s->io_q.size * 2 / 3) {
> +        return ioq_submit(s, true);
>      }
> +
> +    return 0;
>  }
>  
>  void laio_io_plug(BlockDriverState *bs, void *aio_ctx)
> @@ -237,7 +290,7 @@ int laio_io_unplug(BlockDriverState *bs, void *aio_ctx, bool unplug)
>      }
>  
>      if (s->io_q.idx > 0) {
> -        ret = ioq_submit(s);
> +        ret = ioq_submit(s, false);
>      }
>  
>      return ret;
> @@ -281,7 +334,9 @@ BlockAIOCB *laio_submit(BlockDriverState *bs, void *aio_ctx, int fd,
>              goto out_free_aiocb;
>          }
>      } else {
> -        ioq_enqueue(s, iocbs);
> +        if (ioq_enqueue(s, iocbs) < 0) {
> +            goto out_free_aiocb;
> +        }
>      }
>      return &laiocb->common;
>  
> @@ -296,12 +351,14 @@ void laio_detach_aio_context(void *s_, AioContext *old_context)
>  
>      aio_set_event_notifier(old_context, &s->e, NULL);
>      qemu_bh_delete(s->completion_bh);
> +    qemu_bh_delete(s->io_q.retry);
>  }
>  
>  void laio_attach_aio_context(void *s_, AioContext *new_context)
>  {
>      struct qemu_laio_state *s = s_;
>  
> +    s->io_q.retry = aio_bh_new(new_context, ioq_submit_retry, s);
>      s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
>      aio_set_event_notifier(new_context, &s->e, qemu_laio_completion_cb);
>  }
>