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Date: Sun, 16 Dec 2012 18:08:53 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20121216160853.GC15790@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v6 12/12] virtio-blk: add
 x-data-plane=on|off performance feature
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Blue Swirl <blauwirbel@gmail.com>, khoa@us.ibm.com, Paolo Bonzini <pbonzini@redhat.com>, Asias He <asias@redhat.com>

On Mon, Dec 10, 2012 at 02:09:45PM +0100, Stefan Hajnoczi wrote:
> @@ -33,6 +34,7 @@ typedef struct VirtIOBlock
>      VirtIOBlkConf *blk;
>      unsigned short sector_mask;
>      DeviceState *qdev;
> +    VirtIOBlockDataPlane *dataplane;
>  } VirtIOBlock;
>  
>  static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)
> @@ -407,6 +409,14 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>          .num_writes = 0,
>      };
>  
> +    /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
> +     * dataplane here instead of waiting for .set_status().
> +     */

By the way which guests are these?

> +    if (s->dataplane) {
> +        virtio_blk_data_plane_start(s->dataplane);
> +        return;
> +    }
> +

By the way it's chunk such as this that I meant: it's not
compiled out even if dataplane is disabled by configure.
Naither is the extra field in the struct.


>      while ((req = virtio_blk_get_request(s))) {
>          virtio_blk_handle_request(req, &mrb);
>      }