linux-kernel - Re: [PATCH] virtio-blk: use VIRTIO_BLK_F_WCE and VIRTIO_BLK_F_CONFIG

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Message-ID: <55EDB809.8090400@redhat.com>
Date:	Mon, 7 Sep 2015 18:15:05 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	"open list:VIRTIO CORE, NET AND BLOCK DRIVERS" 
	<virtualization@...ts.linux-foundation.org>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH] virtio-blk: use VIRTIO_BLK_F_WCE and
 VIRTIO_BLK_F_CONFIG_WCE in virtio1



On 22/08/2015 00:53, Paolo Bonzini wrote:
> VIRTIO_BLK_F_CONFIG_WCE is important in order to achieve good performance
> (up to 2x, though more realistically +30-40%) in latency-bound workloads.
> However, it was removed by mistake together with VIRTIO_BLK_F_FLUSH.
> 
> It will be restored in the next revision of the virtio 1.0 standard, so
> do the same in Linux.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  drivers/block/virtio_blk.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index d4d05f064d39..ea2c17c66dfb 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -478,8 +478,7 @@ static int virtblk_get_cache_mode(struct virtio_device *vdev)
>  				   struct virtio_blk_config, wce,
>  				   &writeback);
>  	if (err)
> -		writeback = virtio_has_feature(vdev, VIRTIO_BLK_F_WCE) ||
> -		            virtio_has_feature(vdev, VIRTIO_F_VERSION_1);
> +		writeback = virtio_has_feature(vdev, VIRTIO_BLK_F_WCE);
>  
>  	return writeback;
>  }
> @@ -840,7 +839,7 @@ static unsigned int features_legacy[] = {
>  static unsigned int features[] = {
>  	VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
>  	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
> -	VIRTIO_BLK_F_TOPOLOGY,
> +	VIRTIO_BLK_F_WCE, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
>  	VIRTIO_BLK_F_MQ,
>  };
>  
> 

Ping?

Paolo
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