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.

Absolutely. Can you share the results btw? Would be very interesting.

> 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
> 
>  

Makes sense to me, however, note that
1. the value controlled from the host is actually the max queue size
   not the queue size. queue size can be controlled from guest with
   the recent reset extension
2. different sizes for rx and tx probably make sense

-- 
MST

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