Re: [dpdk-dev] [PATCH v4 1/2] net/mlx5: add support for Rx queue delay drop

[Slava Ovsiienko <viacheslavo@nvidia.com>]

> -----Original Message-----
> From: Bing Zhao <bingz@nvidia.com>
> Sent: Thursday, November 4, 2021 19:59
> To: Slava Ovsiienko <viacheslavo@nvidia.com>; Matan Azrad
> <matan@nvidia.com>
> Cc: dev@dpdk.org; Raslan Darawsheh <rasland@nvidia.com>; NBU-Contact-
> Thomas Monjalon <thomas@monjalon.net>; Ori Kam <orika@nvidia.com>
> Subject: [PATCH v4 1/2] net/mlx5: add support for Rx queue delay drop
> 
> For the Ethernet RQs, if there all receiving descriptors are exhausted, the
> packets being received will be dropped. This behavior prevents slow or
> malicious software entities at the host from affecting the network. While for
> hairpin cases, even if there is no software involved during the packet
> forwarding from Rx to Tx side, some hiccup in the hardware or back pressure
> from Tx side may still cause the descriptors to be exhausted. In certain
> scenarios it may be preferred to configure the device to avoid such packet
> drops, assuming the posting of descriptors will resume shortly.
> 
> To support this, a new devarg "delay_drop_en" is introduced, by default, the
> delay drop is enabled for hairpin Rx queues and disabled for standard Rx
> queues. This value is used as a bit mask:
>   - bit 0: enablement of standard Rx queue
>   - bit 1: enablement of hairpin Rx queue And this attribute will be applied to
> all Rx queues of a device.
> 
> The "rq_delay_drop" capability in the HCA_CAP is checked before creating
> any queue. If the hardware capabilities do not support this delay drop, all the
> Rx queues will still be created without this attribute, and the devarg setting
> will be ignored even if it is specified explicitly.
> 
> Signed-off-by: Bing Zhao <bingz@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>