Re: [Qemu-devel] [PATCH] HLFS driver for QEMU

[harryxiyou]

On Mon, Mar 18, 2013 at 7:10 PM, Stefan Hajnoczi <address@hidden> wrote:
[...]
> read/write/flush should be either .bdrv_co_* or .bdrv_aio_*.
>
> The current code pauses the guest while I/O is in progress!  Try running
> disk I/O benchmarks inside the guest and you'll see that performance and
> interactivity are poor.
>
> QEMU has two ways of implementing efficient block drivers:
>
> 1. Coroutines - .bdrv_co_*
>
> Good for image formats or block drivers that have internal logic.
>
> Each request runs inside a coroutine - see include/block/coroutine.h.
> In order to wait for I/O, submit an asynchronous request or worker
> thread and yield the coroutine.  When the request completes, re-enter
> the coroutine and continue.
>
> Examples: block/sheepdog.c or block/qcow2.c.
>
> 2. Asynchronous I/O - .bdrv_aio_*
>
> Good for low-level block drivers that have little logic.
>
> The request processing code is split into callbacks.  I/O requests are
> submitted and then the code returns back to QEMU's main loop.  When the
> I/O request completes, a callback is invoked.
>
> Examples: block/rbd.c or block/qed.c.
>

HLFS do not use QEMU's AIO way. HLFS, itself,  has realized internal AIO.

-- 
Thanks
Harry Wei