Re: RFC: control virtqueue size by the vdpa tool

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Aug 30, 2022 at 06:22:31AM +0000, Eli Cohen wrote:
>  
> 
> Hi,
> 
>  
> 
> I have been experimenting with different queue sizes with mlx5_vdpa and noticed
> that queue size can affect performance.
> 
> I would like to propose an extension to vdpa tool to allow to specify the queue
> size. Valid values will conform to the max of 32768 specified by the spec.
> 
>  
> 
> “vdpa mgmtdev show” will have another line specifying the valid range for a
> management device which could be narrower than the spec allows. This range will
> be valid for data queues only (not for control VQ).
> 
> Another line will display the default queue size
> 
>  
> 
> Example:
> 
> $ vdpa mgmtdev show
> 
> auxiliary/mlx5_core.sf.6:
> 
>   supported_classes net
> 
>   max_supported_vqs 65
> 
>   dev_features CSUM GUEST_CSUM MTU HOST_TSO4 HOST_TSO6 STATUS CTRL_VQ CTRL_VLAN
> MQ CTRL_MAC_ADDR VERSION_1 ACCESS_PLATFORM
> 
>   data queue range 256-4096
> 
>   default queue size 256
> 
>  
> 
> When you create the vdpa device you can specify the requested value:
> 
> $ vdpa dev add name vdpa-a mgmtdev auxiliary/mlx5_core.sf.6 max_vqp 1 mtu 9000
> queue_size 1024
> 
>  


A follow up question: isn't it enough to control the size
from qemu? do we need ability to control it at the kernel level?

-- 
MST

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