[dpdk-dev] [PATCH] doc: add driver limitation for vhost dequeue zero copy

[Tan, Jianfeng]

Hi Junjie,

> -----Original Message-----
> From: Chen, Junjie J
> Sent: Saturday, February 24, 2018 10:44 PM
> To: yliu at fridaylinux.org; maxime.coquelin at redhat.com; Tan, Jianfeng
> Cc: dev at dpdk.org; Chen, Junjie J
> Subject: [PATCH] doc: add driver limitation for vhost dequeue zero copy
> 
> In vhost-switch example, when binding nic to vfio-pci, dequeue zero
> copy cannot work in VM2NIC mode due to no iommu dma mapping is setup
> for guest memory currently.

IMO, it's a limitation that can be fixed. Do you want to try fixing it?

> 
> Signed-off-by: Junjie Chen <junjie.j.chen at intel.com>
> ---
>  doc/guides/sample_app_ug/vhost.rst | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/guides/sample_app_ug/vhost.rst
> b/doc/guides/sample_app_ug/vhost.rst
> index a4bdc6a..1591a31 100644
> --- a/doc/guides/sample_app_ug/vhost.rst
> +++ b/doc/guides/sample_app_ug/vhost.rst


Besides, we might also need to put such limitation at http://dpdk.org/doc/guides/prog_guide/vhost_lib.html

Thanks,
Jianfeng


> @@ -147,7 +147,10 @@ retries on an RX burst, it takes effect only when rx
> retry is enabled. The
>  default value is 15.
> 
>  **--dequeue-zero-copy**
> -Dequeue zero copy will be enabled when this option is given.
> +Dequeue zero copy will be enabled when this option is given, it is worth to
> +note that if NIC is binded to vfio-pci driver, dequeue zero copy cannot work
> +at VM2NIC mode (vm2vm=0) due to currently we don't setup iommu dma
> mapping for
> +guest memory.
> 
>  **--vlan-strip 0|1**
>  VLAN strip option is removed, because different NICs have different
> behaviors
> --
> 2.0.1