Re: [Qemu-block] [PATCH 05/18] block/mirror: Convert to coroutines

[Fam Zheng]

On Wed, 09/13 20:18, Max Reitz wrote:
> In order to talk to the source BDS (and maybe in the future to the
> target BDS as well) directly, we need to convert our existing AIO
> requests into coroutine I/O requests.
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block/mirror.c | 134 
> +++++++++++++++++++++++++++++++++------------------------
>  1 file changed, 78 insertions(+), 56 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 4664b0516f..2b3297aa61 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -80,6 +80,9 @@ typedef struct MirrorOp {
>      QEMUIOVector qiov;
>      int64_t offset;
>      uint64_t bytes;
> +
> +    /* Set by mirror_co_read() before yielding for the first time */
> +    uint64_t bytes_copied;
>  } MirrorOp;
>  
>  typedef enum MirrorMethod {
> @@ -101,7 +104,7 @@ static BlockErrorAction 
> mirror_error_action(MirrorBlockJob *s, bool read,
>      }
>  }
>  
> -static void mirror_iteration_done(MirrorOp *op, int ret)
> +static void coroutine_fn mirror_iteration_done(MirrorOp *op, int ret)
>  {
>      MirrorBlockJob *s = op->s;
>      struct iovec *iov;
> @@ -138,9 +141,8 @@ static void mirror_iteration_done(MirrorOp *op, int ret)
>      }
>  }
>  
> -static void mirror_write_complete(void *opaque, int ret)
> +static void coroutine_fn mirror_write_complete(MirrorOp *op, int ret)
>  {
> -    MirrorOp *op = opaque;
>      MirrorBlockJob *s = op->s;
>  
>      aio_context_acquire(blk_get_aio_context(s->common.blk));
> @@ -158,9 +160,8 @@ static void mirror_write_complete(void *opaque, int ret)
>      aio_context_release(blk_get_aio_context(s->common.blk));
>  }
>  
> -static void mirror_read_complete(void *opaque, int ret)
> +static void coroutine_fn mirror_read_complete(MirrorOp *op, int ret)
>  {
> -    MirrorOp *op = opaque;
>      MirrorBlockJob *s = op->s;
>  
>      aio_context_acquire(blk_get_aio_context(s->common.blk));
> @@ -176,8 +177,11 @@ static void mirror_read_complete(void *opaque, int ret)
>  
>          mirror_iteration_done(op, ret);
>      } else {
> -        blk_aio_pwritev(s->target, op->offset, &op->qiov,
> -                        0, mirror_write_complete, op);
> +        int ret;
> +
> +        ret = blk_co_pwritev(s->target, op->offset,
> +                             op->qiov.size, &op->qiov, 0);
> +        mirror_write_complete(op, ret);
>      }
>      aio_context_release(blk_get_aio_context(s->common.blk));
>  }
> @@ -242,53 +246,49 @@ static inline void mirror_wait_for_io(MirrorBlockJob *s)
>   *          (new_end - offset) if tail is rounded up or down due to
>   *          alignment or buffer limit.
>   */
> -static uint64_t mirror_do_read(MirrorBlockJob *s, int64_t offset,
> -                               uint64_t bytes)
> +static void coroutine_fn mirror_co_read(void *opaque)
>  {
> +    MirrorOp *op = opaque;
> +    MirrorBlockJob *s = op->s;
>      BlockBackend *source = s->common.blk;
>      int nb_chunks;
>      uint64_t ret;
> -    MirrorOp *op;
>      uint64_t max_bytes;
>  
>      max_bytes = s->granularity * s->max_iov;
>  
>      /* We can only handle as much as buf_size at a time. */
> -    bytes = MIN(s->buf_size, MIN(max_bytes, bytes));
> -    assert(bytes);
> -    assert(bytes < BDRV_REQUEST_MAX_BYTES);
> -    ret = bytes;
> +    op->bytes = MIN(s->buf_size, MIN(max_bytes, op->bytes));
> +    assert(op->bytes);
> +    assert(op->bytes < BDRV_REQUEST_MAX_BYTES);
> +    op->bytes_copied = op->bytes;
>  
>      if (s->cow_bitmap) {
> -        ret += mirror_cow_align(s, &offset, &bytes);
> +        op->bytes_copied += mirror_cow_align(s, &op->offset, &op->bytes);
>      }
> -    assert(bytes <= s->buf_size);
> +    /* Cannot exceed BDRV_REQUEST_MAX_BYTES + INT_MAX */
> +    assert(op->bytes_copied <= UINT_MAX);
> +    assert(op->bytes <= s->buf_size);
>      /* The offset is granularity-aligned because:
>       * 1) Caller passes in aligned values;
>       * 2) mirror_cow_align is used only when target cluster is larger. */
> -    assert(QEMU_IS_ALIGNED(offset, s->granularity));
> +    assert(QEMU_IS_ALIGNED(op->offset, s->granularity));
>      /* The range is sector-aligned, since bdrv_getlength() rounds up. */
> -    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> -    nb_chunks = DIV_ROUND_UP(bytes, s->granularity);
> +    assert(QEMU_IS_ALIGNED(op->bytes, BDRV_SECTOR_SIZE));
> +    nb_chunks = DIV_ROUND_UP(op->bytes, s->granularity);
>  
>      while (s->buf_free_count < nb_chunks) {
> -        trace_mirror_yield_in_flight(s, offset, s->in_flight);
> +        trace_mirror_yield_in_flight(s, op->offset, s->in_flight);
>          mirror_wait_for_io(s);
>      }
>  
> -    /* Allocate a MirrorOp that is used as an AIO callback.  */
> -    op = g_new(MirrorOp, 1);
> -    op->s = s;
> -    op->offset = offset;
> -    op->bytes = bytes;
> -
>      /* Now make a QEMUIOVector taking enough granularity-sized chunks
>       * from s->buf_free.
>       */
>      qemu_iovec_init(&op->qiov, nb_chunks);
>      while (nb_chunks-- > 0) {
>          MirrorBuffer *buf = QSIMPLEQ_FIRST(&s->buf_free);
> -        size_t remaining = bytes - op->qiov.size;
> +        size_t remaining = op->bytes - op->qiov.size;
>  
>          QSIMPLEQ_REMOVE_HEAD(&s->buf_free, next);
>          s->buf_free_count--;
> @@ -297,53 +297,75 @@ static uint64_t mirror_do_read(MirrorBlockJob *s, 
> int64_t offset,
>  
>      /* Copy the dirty cluster.  */
>      s->in_flight++;
> -    s->bytes_in_flight += bytes;
> -    trace_mirror_one_iteration(s, offset, bytes);
> +    s->bytes_in_flight += op->bytes;
> +    trace_mirror_one_iteration(s, op->offset, op->bytes);
>  
> -    blk_aio_preadv(source, offset, &op->qiov, 0, mirror_read_complete, op);
> -    return ret;
> +    ret = blk_co_preadv(source, op->offset, op->bytes, &op->qiov, 0);
> +    mirror_read_complete(op, ret);
>  }
>  
> -static void mirror_do_zero_or_discard(MirrorBlockJob *s,
> -                                      int64_t offset,
> -                                      uint64_t bytes,
> -                                      bool is_discard)
> +static void coroutine_fn mirror_co_zero(void *opaque)
>  {
> -    MirrorOp *op;
> +    MirrorOp *op = opaque;
> +    int ret;
>  
> -    /* Allocate a MirrorOp that is used as an AIO callback. The qiov is 
> zeroed
> -     * so the freeing in mirror_iteration_done is nop. */
> -    op = g_new0(MirrorOp, 1);
> -    op->s = s;
> -    op->offset = offset;
> -    op->bytes = bytes;
> +    op->s->in_flight++;
> +    op->s->bytes_in_flight += op->bytes;
>  
> -    s->in_flight++;
> -    s->bytes_in_flight += bytes;
> -    if (is_discard) {
> -        blk_aio_pdiscard(s->target, offset,
> -                         op->bytes, mirror_write_complete, op);
> -    } else {
> -        blk_aio_pwrite_zeroes(s->target, offset,
> -                              op->bytes, s->unmap ? BDRV_REQ_MAY_UNMAP : 0,
> -                              mirror_write_complete, op);
> -    }
> +    ret = blk_co_pwrite_zeroes(op->s->target, op->offset, op->bytes,
> +                               op->s->unmap ? BDRV_REQ_MAY_UNMAP : 0);
> +    mirror_write_complete(op, ret);
> +}
> +
> +static void coroutine_fn mirror_co_discard(void *opaque)
> +{
> +    MirrorOp *op = opaque;
> +    int ret;
> +
> +    op->s->in_flight++;
> +    op->s->bytes_in_flight += op->bytes;
> +
> +    ret = blk_co_pdiscard(op->s->target, op->offset, op->bytes);
> +    mirror_write_complete(op, ret);
>  }
>  
>  static unsigned mirror_perform(MirrorBlockJob *s, int64_t offset,
>                                 unsigned bytes, MirrorMethod mirror_method)
>  {
> +    MirrorOp *op;
> +    Coroutine *co;
> +    unsigned ret = bytes;
> +
> +    op = g_new(MirrorOp, 1);
> +    *op = (MirrorOp){
> +        .s      = s,
> +        .offset = offset,
> +        .bytes  = bytes,
> +    };
> +
>      switch (mirror_method) {
>      case MIRROR_METHOD_COPY:
> -        return mirror_do_read(s, offset, bytes);
> +        co = qemu_coroutine_create(mirror_co_read, op);
> +        break;
>      case MIRROR_METHOD_ZERO:
> +        co = qemu_coroutine_create(mirror_co_zero, op);
> +        break;
>      case MIRROR_METHOD_DISCARD:
> -        mirror_do_zero_or_discard(s, offset, bytes,
> -                                  mirror_method == MIRROR_METHOD_DISCARD);
> -        return bytes;
> +        co = qemu_coroutine_create(mirror_co_discard, op);
> +        break;
>      default:
>          abort();
>      }
> +
> +    qemu_coroutine_enter(co);
> +
> +    if (mirror_method == MIRROR_METHOD_COPY) {
> +        /* Same assertion as in mirror_co_read() */
> +        assert(op->bytes_copied <= UINT_MAX);
> +        ret = op->bytes_copied;
> +    }

This special casing is a bit ugly. Can you just make mirror_co_zero and
mirror_co_discard set op->bytes_copied too? (and perhaps rename to
op->bytes_handled) If so the comment in MirrorOp needs an update too.

And is it better to initialize it to -1 before entering coroutine, then assert
it is != -1 afterwards?

> +
> +    return ret;
>  }
>  
>  static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
> -- 
> 2.13.5
> 

Fam