Re: [dpdk-dev] [PATCH] net/mlx5: set RSS key len 0 to indicate default RSS

[Shahaf Shuler <shahafs@mellanox.com>]

Hi Ophir,

To add on top of Koh's comment

Wednesday, October 3, 2018 9:56 PM, Yongseok Koh:
> Subject: Re: [PATCH] net/mlx5: set RSS key len 0 to indicate default RSS
> > On Oct 3, 2018, at 10:37 AM, Ophir Munk <ophirmu@mellanox.com>
> wrote:
> >
> > Applications which add an RSS flow must supply an RSS key table and an
> > RSS key length. If an application needs to add the default RSS flow it
> > should not care about the exact RSS default key table and its length.
> > By setting key length to 0 - the PMD will know that it should use the
> > default RSS key table and length.

Can you refer where in the rte_flow API this is documented?  I couldn't find it under struct rte_flow_action_rss  definition. 
I agree it is better for the PMD to behave this way, but this should be explained in the API, so for this patch to be accepted we need also doc update in rte_flow.h.

In my opinion, it is better for the key to be NULL to request from the PMD to use the default key, similar to struct rte_eth_rss_conf. 

> >
> > Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
> > ---
> > drivers/net/mlx5/mlx5_flow.c | 7 ++++---
> 
> Please rebase the code on top of the latest dpdk-next-net-mlx.
> Actually, it is better to rebase on top of PR#878.
> 
> Thanks,
> Yongseok
> 
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/mlx5/mlx5_flow.c
> > b/drivers/net/mlx5/mlx5_flow.c index 3f548a9..18eacf5 100644
> > --- a/drivers/net/mlx5/mlx5_flow.c
> > +++ b/drivers/net/mlx5/mlx5_flow.c
> > @@ -2062,7 +2062,8 @@ struct mlx5_flow_tunnel_info {
> >
> RTE_FLOW_ERROR_TYPE_ACTION_CONF,
> > 					  &rss->level,
> > 					  "tunnel RSS is not supported");
> > -	if (rss->key_len < MLX5_RSS_HASH_KEY_LEN)
> > +	/* key_len 0 means using default RSS key */
> > +	if (rss->key_len > 0 && rss->key_len < MLX5_RSS_HASH_KEY_LEN)
> > 		return rte_flow_error_set(error, ENOTSUP,
> >
> RTE_FLOW_ERROR_TYPE_ACTION_CONF,
> > 					  &rss->key_len,
> > @@ -2106,7 +2107,7 @@ struct mlx5_flow_tunnel_info {
> > 		memcpy((*flow->queue), rss->queue,
> > 		       rss->queue_num * sizeof(uint16_t));
> > 	flow->rss.queue_num = rss->queue_num;
> > -	memcpy(flow->key, rss->key, MLX5_RSS_HASH_KEY_LEN);
> > +	memcpy(flow->key, rss->key, rss->key_len);

In Mellanox devices 40B of a key is a must. If you intended to copy 0 bytes, it is better to do it in other ways. 
 
> > 	flow->rss.types = rss->types;
> > 	flow->rss.level = rss->level;
> > 	flow->fate |= MLX5_FLOW_FATE_RSS;
> > @@ -2948,7 +2949,7 @@ struct mlx5_flow_tunnel_info {
> > 					     flow->rss.queue_num);
> > 			if (!hrxq)
> > 				hrxq = mlx5_hrxq_new(dev, flow->key,
> > -
> MLX5_RSS_HASH_KEY_LEN,
> > +						     flow->rss.key_len,
> > 						     verbs->hash_fields,
> > 						     (*flow->queue),
> > 						     flow->rss.queue_num,
> > --
> > 1.8.3.1
> >