Re: [dpdk-dev] [PATCH] net/virtio: fix AVX512 datapath selection

["Liu, Yong" <yong.liu@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Monday, May 11, 2020 10:47 PM
> To: Liu, Yong <yong.liu@intel.com>; Ye, Xiaolong <xiaolong.ye@intel.com>;
> Yigit, Ferruh <ferruh.yigit@intel.com>; dev@dpdk.org
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> Subject: [PATCH] net/virtio: fix AVX512 datapath selection
> 
> The AVX512 packed ring datapath selection was only done
> at build time, but it should also be checked at runtime
> that the CPU supports it.
> 
> This patch add a CPU flags check so that non-vectorized
> path is selected at runtime if AVX512 is not supported.
> 
> Fixes: ccb10995c2ad ("net/virtio: add election for vectorized path")
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  drivers/net/virtio/virtio_ethdev.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> index 312871cb48..49ccef12c7 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -1965,8 +1965,10 @@ eth_virtio_dev_init(struct rte_eth_dev *eth_dev)
>  			PMD_DRV_LOG(INFO,
>  				"building environment do not support
> packed ring vectorized");
>  #else
> -			hw->use_vec_rx = 1;
> -			hw->use_vec_tx = 1;
> +			if
> (rte_cpu_get_flag_enabled(RTE_CPUFLAG_AVX512F)) {
> +				hw->use_vec_rx = 1;
> +				hw->use_vec_tx = 1;
> +			}
>  #endif

Hi Maxime,
Here is pre-setting for vectorized path selection, virtio_dev_configure will do second time check. 
Running environment will be checked in second time check.  We can move some checks from virtio_dev_configure to here, but is it needed to do that?

BTW, both split ring and packed ring will utilized this setting, it will break split vectorized datapath is server not has AVX512F flag.
And it may cause building issue on those platforms which not defined RTE_CPUFLAG_AVX512F.

Thanks,
Marvin

>  		}
>  	}
> --
> 2.25.4