Re: [PATCH 1/2] linux-aio: use LinuxAioState from the running thread

[Kevin Wolf <kwolf@redhat.com>]

Am 09.06.2022 um 15:44 hat Emanuele Giuseppe Esposito geschrieben:
> From: Paolo Bonzini <pbonzini@redhat.com>
> 
> Remove usage of aio_context_acquire by always submitting asynchronous
> AIO to the current thread's LinuxAioState.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  block/file-posix.c  |  3 ++-
>  block/linux-aio.c   | 13 ++++++-------
>  include/block/aio.h |  4 ----
>  3 files changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 48cd096624..33f92f004a 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -2086,7 +2086,8 @@ static int coroutine_fn raw_co_prw(BlockDriverState *bs, uint64_t offset,
>  #endif
>  #ifdef CONFIG_LINUX_AIO
>      } else if (s->use_linux_aio) {
> -        LinuxAioState *aio = aio_get_linux_aio(bdrv_get_aio_context(bs));
> +        AioContext *ctx = qemu_get_current_aio_context();
> +        LinuxAioState *aio = aio_get_linux_aio(ctx);
>          assert(qiov->size == bytes);
>          return laio_co_submit(bs, aio, s->fd, offset, qiov, type,
>                                s->aio_max_batch);

raw_aio_plug() and raw_aio_unplug() need the same change.

I wonder if we should actually better remove the 'aio' parameter from
the functions that linux-aio.c offers to avoid suggesting that any
LinuxAioState works for any thread. Getting it from the current
AioContext is something it can do by itself. But this would be code
cleanup for a separate patch.

> diff --git a/block/linux-aio.c b/block/linux-aio.c
> index 4c423fcccf..1d3cc767d1 100644
> --- a/block/linux-aio.c
> +++ b/block/linux-aio.c
> @@ -16,6 +16,9 @@
>  #include "qemu/coroutine.h"
>  #include "qapi/error.h"
>  
> +/* Only used for assertions.  */
> +#include "qemu/coroutine_int.h"
> +
>  #include <libaio.h>
>  
>  /*
> @@ -56,10 +59,8 @@ struct LinuxAioState {
>      io_context_t ctx;
>      EventNotifier e;
>  
> -    /* io queue for submit at batch.  Protected by AioContext lock. */
> +    /* All data is only used in one I/O thread.  */
>      LaioQueue io_q;
> -
> -    /* I/O completion processing.  Only runs in I/O thread.  */
>      QEMUBH *completion_bh;
>      int event_idx;
>      int event_max;
> @@ -102,9 +103,8 @@ static void qemu_laio_process_completion(struct qemu_laiocb *laiocb)
>       * later.  Coroutines cannot be entered recursively so avoid doing
>       * that!
>       */
> -    if (!qemu_coroutine_entered(laiocb->co)) {
> -        aio_co_wake(laiocb->co);
> -    }
> +    assert(laiocb->co->ctx == laiocb->ctx->aio_context);
> +    qemu_coroutine_enter_if_inactive(laiocb->co);
>  }
>  
>  /**
> @@ -238,7 +238,6 @@ static void qemu_laio_process_completions_and_submit(LinuxAioState *s)
>      if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
>          ioq_submit(s);
>      }
> -    aio_context_release(s->aio_context);
>  }

I certainly expected the aio_context_acquire() in the same function to
go away, too! Am I missing something?

Kevin