linux-kernel - Re: [PATCH v3 1/2] include/uapi/linux/virtio_blk.h: introduce feature of VIRTIO_BLK_F

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Date:	Sun, 29 Jun 2014 19:32:16 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-api@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 1/2] include/uapi/linux/virtio_blk.h: introduce
 feature of VIRTIO_BLK_F_MQ

On Thu, Jun 26, 2014 at 05:41:47PM +0800, Ming Lei wrote:
> Current virtio-blk spec only supports one virtual queue for transfering
> data between VM and host, and inside VM all kinds of operations on
> the virtual queue needs to hold one lock, so cause below problems:
> 
> 	- bad scalability
> 	- bad throughput
> 
> This patch requests to introduce feature of VIRTIO_BLK_F_MQ
> so that more than one virtual queues can be used to virtio-blk
> device, then above problems can be solved or eased.
> 
> Signed-off-by: Ming Lei <ming.lei@...onical.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  include/uapi/linux/virtio_blk.h |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
> index 6d8e61c..9ad67b2 100644
> --- a/include/uapi/linux/virtio_blk.h
> +++ b/include/uapi/linux/virtio_blk.h
> @@ -40,6 +40,7 @@
>  #define VIRTIO_BLK_F_WCE	9	/* Writeback mode enabled after reset */
>  #define VIRTIO_BLK_F_TOPOLOGY	10	/* Topology information is available */
>  #define VIRTIO_BLK_F_CONFIG_WCE	11	/* Writeback mode available in config */
> +#define VIRTIO_BLK_F_MQ		12	/* support more than one vq */
>  
>  #ifndef __KERNEL__
>  /* Old (deprecated) name for VIRTIO_BLK_F_WCE. */
> @@ -77,6 +78,10 @@ struct virtio_blk_config {
>  
>  	/* writeback mode (if VIRTIO_BLK_F_CONFIG_WCE) */
>  	__u8 wce;
> +	__u8 unused;
> +
> +	/* number of vqs, only available when VIRTIO_BLK_F_MQ is set */
> +	__u16 num_queues;
>  } __attribute__((packed));
>  
>  /*
> -- 
> 1.7.9.5
--
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